Exam "4": Microbial Symbiosis with Humans, Epidemiology, Person-to-Person Diseases, Vector-Borne Diseases, Food- and Water-Borne Diseases, and Eukaryotic Pathogens (Bio 286- Microbiology) Flashcards
microbiome
functional collection of different microbes in a particular system
microbiota
all microbes in a microhabitat
host microbiome supraorganism
a body and all of its associated microbiota
relationship between humans and their microbiota
commensalistic
overview of human microbiome
approximately 4x10^13 MICROBES IN A HUMAN MICROBIOME and only about 3x10^13 HUMAN CELLS
most of the human microbiota is located in the
colon
gastrointestinal microbiota
humans are monogastric and omnivorous… colonization of gut begins at birth… consists of stomach, small intestine, and large intestine… comprises 400 m^2 of surface area… responsible for digestion of food, absorption of nutrients, and production of nutrients by indigenous microbial flora… contains 10^13 to 10^14 microbial cells
stomach and small intestine
microbial populations in different areas of GI tract are influenced by diet and physical conditions in area… acidity of stomach and duodenum of small intestine (~pH 2) prevent many organisms from colonizing GI tract, but there is a rich microbiome in healthy stomach… FIRMICUTES, BACTERIODETES, and Actinobacteria are common in gastric fluid, while Firmicutes and PROTEOBACTERIA are common in mucus layer in stomach… HELICOBACTER PYLORI was discovered in 1980s and has since been found in ~50% of world’s population– when present, it is found in gastric mucosa
common bacterial phyla of gut
FIRMICUTES, BACTERIODES, and PROTEOBACTERIA
Helicobacter pylori are found in the
STOMACH
large intestine
intestinal microorganisms carry out a variety of essential metabolic reactions that produce various compounds… colon is essentially an in vitro fermentation vessel, with the microbiota using nutrients derived from digestion of food… most organisms are restricted to lumen of large intestine, while others are in mucosal layers
gut enterotypes
each type is functionally and phylogenetically distinct… three types: 1. enriched in Bacteriodes… 2. enriched in Prevotella… 3. enriched in Ruminococcus
gastrointestinal microbiota roles
products of intestinal microbiota and “educating” the immune system… many microbial metabolites or transformation products that can be generated in gut have significant influence on host physiology (vitamin production, modification of steroids, or amino acid biosynthesis)
human gut microbiome functions
production of essential amino acids and vitamins… maturation of gastrointestinal tract… production of volatile fatty acids from polysaccharides
increased methane production in gut leads to
elevated volatile fatty acid production
oral cavity
is a complex/heterogeneous microbial habitat… saliva contains antimicrobial enzymes… high concentrations of nutrients near surfaces in mouth promote localized microbial growth… tooth consists of a mineral matrix (enamel) surrounding living tissue, the dentin, and pulp
airways
microbes thrive in upper respiratory tract (sinuses, nasopharynx, oropharynx, oral cavity, larynx)… bacteria continually enter respiratory tract from air during breathing– most are trapped in mucus of nasal and oral passages and expelled with nasal secretions or swallowed and then killed in stomach… the lower respiratory tract (trachea, bronchi, lungs) has no normal microbiota in healthy adults– ciliated mucosal cells move particles up and out of lungs
microorganism most associated with dental cavities
streptococci
urogenital tracts and their microbes
altered conditions can cause potential pathogens in urethra (such as Escherichia coli and Proteus mirabilis) to multiply and cause disease– E.coli and P.mirabilis frequently cause urinary tract infections in women…. fungal overgrowth (candida albicans) possible… the vagina is weakly acidic and contains significant amounts of glycogen… Lactobacillus acidophilus (resident organism of vagina) ferments the glycogen to produce lactic acid (lactic acid maintains a local acidic environment)…. vaginitis commonly results from overgrowth of Candida and Trichomonas vaginalis
most numerous bacteria on skin
actinobacteria
skin and its microbes
there are approximately 1 million resident bacteria per square centimeter of skin for a total of 10^10 skin microorganisms covering average adult… skin surface varies greatly in chemical composition and moisture content… three microenvironments: dry, moist, and sebaceous… composition is influenced by: environmental factors and host factors… each microenvironment shows an unique microbiota
human microbiome study groups
have formed most of our understanding of the functions of human microbiome… human microbiome project (HMP) surveyed hundred of medical students over several years to determine a baseline for healthy human microbiomes…later projects showed the weakness in this model, as they revealed more diversity in non-US born subjects and lacked data on diet or other lifestyle attributes
animal models
while there are significant differences between mice and humans, mice have been used to good effect to study human gut microbiome interactions… mice have a larger colon and cecum than humans… most fermentation is completed in the mouse cecum rather than the human large intestine… mice models: have a short life cycle and well-defined genetic lines, can be raised in a germ-free environment, can have antibiotic therapy, strict dietary control, fecal transplants
colonization and succession
COLONIZATION BEGINS AT BIRTH WITH TRANSFER FROM MOTHER TO INFANT– early colonizing microbes are a source of vitamins and tend to be facultative rather than obligate anaerobes… variables determine the nature of the gut microbiome– vaginally born infants have a microbiome more similar to that of their mothers than those born via c-section (infants born via C-section have less Bacteriodes than vagina babies); breastfed infants have more commensal bacteria as breast milk has oligosaccharides that promote their colonization
when does colonization begin?
at birth
following antibiotic therapy, patients are often administered
probiotics to facilitate recolonization of normal microbiota in intestines
stability of adult microbiome and transitions with age
early experiences determine gut microbiome… aging and frailty are associated with decreased microbial diversity
inflammatory bowel disease (IBD)
chronic inflammation of gut and disruption of homeostasis (dysbiosis)… antibiotic use increases the risk of development… once developed, it may be transmissible between family members… individuals with this have lower gut microbiome diversity
role of gut microbiota in obesity: mouse models
Normal mice have 40 percent more fat than germ-free mice with the same diet. When germ-free mice were given normal mouse microbiota, they started gaining weight… Mice that are genetically obese have different microbiota than normal mice. Obese mice have more Firmicutes… mice grown in absence of microbes then are inoculated with healthy cecal material from other mice have genes associated with glucose uptake, lipid absorption, and lipid transport activated so the mice gains body fat without increasing energy intake
dental cavities and periodontitis
cells form a biofilm called dental plaque, which as Streptococcus and other fermenting bacteria… these fermenters produce acid, which wears down the tooth enamel… periodontal disease is thought to contribute to several systemic conditions, including cardiovascular disease and arthritis
antibiotics and human microbiome
Oral antibiotics decrease ALL microbes in the human gut (both target and non-target)… Use of antibiotics during the first few months of life increases the risk of developing IBD and other disorders related to dysbiosis…Clostridium difficile infections tend to occur following antibiotic treatment– C.difficile is a spore former and generally antibiotic resistant; the newer therapy for C.difficle infection is a fecal transplant
probiotics
live organisms that confer a health benefit to the host
Bifidobacterium and Lactobacillus
commonly used probiotics found in yogurt and probiotic drinks.. they may work by taking up space or nutrients, limiting the ability of pathogens to colonize the gut
prebiotics
typically carbohydrates that are indigestible by human hosts, but provide nutrition for fermentative gut bacteria
epidemiology
study of occurrence, distribution, and determinants of health and disease in a population
public health
health of a population as a whole
surveillance
the observation, recognition, and reporting of diseases as they occur
incidence
number of new cases of the disease in a given period of time
prevalence
total number of new and existing cases in a population in a given time
epidemic
disease that occurs in a large number of people in a population at the same time; is localized/geographically defined
pandemic
disease that occurs widespread, usually worldwide; passes geographical borders
endemic
disease that is constantly present in a population but usually at low incidences; constant, low level presence
sporadic
disease that occurs randomly, no pattern to incidence of disease
occurrence of Lyme Disease in Michigan is an
endemic
outbreak
occurs when a number of cases of a disease are reported in a short period of time
stage of disease
- infection… 2. incubation period… 3. acute period… 4. decline period… 5. convalescent period
infection
organism invades and colonizes the host… microbes are within host
incubation period
time between infection and onset of symptoms
acute period
disease is at its height
decline period
disease symptoms are subsiding
convalescent period
patient regains strength and returns to normal
chronic infections
host and pathogen survive
acute infections
pathogen can be selective force
mortality
incidence of death in a population
morbidity
disease refers to incidence of disease, including fatal and nonfatal diseases
disability-adjusted life year (DALY)
quantitatively measures disease burdens in terms of lost years due to disease, disability due to disease, and premature death
coevolution
Process by which two species evolve in response to changes in each other– of a host and a pathogen: the virulence of the pathogen in host-to-host transmission decreases while the resistance of host increases… but if a pathogen does not rely on host-to-host transmission then it will remain extremely virulent… saves “best of fit” diseases– decreased toxicity but increased communicability
herd immunity
resistance of a group to infection due to immunity of a high proportion of group… if a high proportion of individuals are immune to an infection then whole population will be protected… immunized people protect nonimmunized people because the pathogen cannot be passed on so the cycle of infectivity is broken… 1-1/Ro = __% of people needed to be immunized to be successful
common stages in mechanisms of transmission
escape from host, travel, and entry into new host
direct host to host transmission
infected individual transmits a disease directly to a susceptible host without assistance of an intermediary (ex: flu, common cold, STDs, ringworm)
indirect host to host transmission
occurs when transmission is facilitated by a living (vector) or nonliving (fomite) agent
vector
living agents of transmission
fomite
nonliving agents of transmission; inanimate object that can transmit disease
mechanical vector
arthropod that carries infection but is not itself infected
biological vector
arthropod that carries infection and is itself infected
reservoir
sites in which infectious agents remain viable and from which individuals can become infected
zoonosis
any disease that primarily infects animals but is occasionally transmitted to humans
common source epidemic
usually arises from contamination of water or food… endemic indicated by a sharp rise in number of cases reported daily over a brief interval (ex: cholera)
John Snow
one of the first epidemiologists, studied epidemiology of cholera
host to host epidemic
disease shows a slow, progressive rise and a gradual decline (ex: influenza, chicken pox)
carriers
pathogen infected individuals showing no signs of clinical disease… potential sources of infections… can be identified using diagnostic techniques, including culture and immunoassays… 1/4 of all people (ex: typhoid mary)
basic reproduction number (Ro)
number of expected secondary cases of a given disease from each single case… mathematical model assumes an entirely susceptible population… the larger the Ro, the more likely a chain infection will occur
vehicles
a mode of transmission reliant on medium/media… common examples include food, air, and water
infectious disease controls directed against common vehicles
food laws lowered incidence of foodborne pathogens… water purification reduced incidence of typhoid fever (filtration, chlorination)… airborne pathogens are difficult to control
infectious disease controls directed against reservoir
if reservoir is an animal it can be immunized or destroyed…. if reservoir is human then they can be quarantined, immunized, and treated
infectious disease controls directed against transmission of pathogen
immunization, quarantine, and surveillance
quarantine
restricts movement of an individual with active infection
pathogen eradication
goal is to remove all of a pathogen from any reservoirs (ex: smallpox, polio// potentially someday rabies, leprosy)
emergent
diseases that suddenly become prevalent
reemergent
diseases that have become prevalent after having been under control
emergence factors
human demographics and behaviour… technology and industry… economic development and land use… international travel and commerce… microbial adaptation and change… breakdown of public health measures… abnormal natural occurrences
key elements of addressing emerging diseases
recognition of disease… intervention to prevent pathogen transmission (methods include quarantine, immunization, and drug treatment)
acquired immunodeficiency syndrome (AIDS)
viral disease that attacks immune system… first reported cases were in US in 1981… at least 70 million people have been infected worldwide with HIV and more than 25 million people have died from AIDS… studies in US suggest virus was transmitted through sexual contact or blood… rapid pathogen adaptation and change has contributed to HIV/AIDS epidemic… does not require quarantine
cholera
causes severe water-loss diarrhea… typically transmitted through ingestion of contaminated water containing Vibrio cholerae… largely restricted to developing countries… endemic in Africa/Southease Asia/Indian subcontinent/Central and South America… can be controlled by application of water treatment… 100,000 deaths per year
influenza
pandemics occur every 10-40 years… caused by major change in influenza genome (antigenic drift and antigenic shift)… occurs cyclically because more strains emerge due to reassortment between bird/swine/and human variants…. ex: 2009 swine flu pandemic (H1N1 influenza)– swine in Mexico simultaneously infected with swine influenza, bird influenza, and human influenza
antigenic drift
minor change in influenza viral antigens due to gene mutation
antigenic shift
major change in influenza virus antigen due to gene reassortment
biological warfare
use of biological agents to kill a military or civilian population
potential candidates for biological warfare
can by virtually any pathogenic bacterium or virus… is easy to produce and deliver… safe for use by offensive soldiers… able to incapacitate/kill individuals under attack in a consistent and reproducible manner`
anthrax in biological warfare
Bacillus anthracis is a preferred agent for biological warfare and biological terrorism because endospores enhance ability to disseminate B.anthracis in aerosols… three forms of disease: cutaneous, gastrointestinal, and pulmonary… anthrax is treated with ciprofloxacin
airborne pathogens
aerosols are important for person-to-person transmission of many infectious diseases… most pathogens survive poorly in air; thus, they are effectively transmitted only over short distances
respiratory infections
different pathogens characteristically colonize the respiratory tract at different levels… the upper and lower respiratory tracts offer different environments (temperature, air flow, pH) and favor different microbes
upper respiratory tract
nasal cavity, oral cavity, pharynx, larynx
lower respiratory tract
trachea, primary/secondary bronchus, respiratory bronchiole, terminal bronchus, alveolar ducts, alveolar sacs, and alveoli
streptococcus pyogenes
aka GROUP A STREPTOCOCCI… commonly found in low numbers in upper respiratory tract of healthy individuals… can cause pus-forming wounds… causative agent of STREP THROAT… can also cause infections of inner ear, mammary glands, and skin as IMPETIGO… ERYSIPELAS is an acute streptococcal skin infection… host defenses are weakened or a new, highly virulent strain is introduced… certain group A streptococci strains carry a lysogenic bacteriophage that encodes exotoxins responsible for symptoms of STREPTOCOCCAL TOXIC SHOCK SYNDROME and scarlet fever… untreated or insufficiently treated infections can lead to other diseases (ex: RHEUMATIC FEVER due to molecular mimicry between streptococci’s M protein and host tissue)… occasionally causes sudden and severe systemic infections– CELLULITIS (subcutaneous skin infection) and NECROTIXING FASCITIS (flesh eating bacteria)
streptococcus pneumoniae
LEADING CAUSE OF BACTERIAL PNEUMONIA… gram positive diplococci (will be present in sputum sample if infected)… virulence factor: ENCAPSULATED strains are pathogenic bacteria because they are harder to kill… treatable by antimicrobial agents (as are group A streptococci) but drug resistant strains are common
diphtheria
severe respiratory disease that typically infects children… caused by CORYNEBACTERIUM DIPHTHERIAE (a bacterium that forms irregular rods during growth)… preventable and treatable… PATHOGENIC STRAINS OF C. DIPHTHERIAE LYSOGENZIED BY BETA-BACTERIOPHAGE PRODUCE A POWERFUL EXOTOXIN that causes: tissue death due to prevention of protein synthesis and a PSEUDOMEMBRANE in patient’s throat
pertussis (whooping cough)
an acute, highly infectious respiratory disease… caused by infection with BORDETELLA PERTUSSIS (gram negative, secretes exotoxin)… observed frequently in school-age children… characterized by a recurrent, violent cough… has been a consistent upward trend of infections since 1980s… inadequately immunized children/adolescents/adults are at high risk for acquiring/spreading pertussis
tuberculosis
caused by Mycobacterium tuberculosis… worldwide infectious disease of humans… incidence is increasing… M.tuberculosis is transmitted by airborne droplets… cell mediated immunity plays a critical role in preventing active disease after infection… classified as a PRIMARY INFECTION (initial infection) or POSTPRIMARY INFECTION (reinfection)… spread of tuberculosis is prevented by: hospitalization of patients in negative-pressure rooms and use of face masks for healthcare workers… treatment: antimicrobial therapy with ISONIAZID; usually involves a nine-month regimen (affects the synthesis of mycolic acid in mycobacteria); directly observed therapy (DOT) is popular in some areas to assure compliance with doctor’s orders and reduce risk of antibiotic resistance
leprosy (Hansen’s Disease)
is caused by Mycobacterium leprae… armadillo is only experimental animal that has been successfully used to grow M.leprae… most serious form is characterized by folded, bulblike lesions on the body
mycobacterium
ACID-FAST because of the waxy MYCOLIC ACID content of their cell walls… are multidrug resistant (and extreme-drug resistant)
meningitis
inflammation of meninges (membranes that line the central nervous system, especially the spinal cord and brain)… can be caused by viral, bacterial, fungal, or protist infections
neisseria meningitidis
gram negative, nonsporulating, obligately aerobic, oxidase-positive, encapsulated DIPLOCOCCUS… causes one type of infectious bacterial meningitis and a related infection, meningococcemia
MMR (measles, mumps, and rubella) and Varicella -Zoster Infections
viruses are less easily controlled by chemotherapeutic methods… the most prevalent human infections are caused by viruses… most viral diseases are acute/self-limiting infections… a few serious viral diseases have been effectively controlled by vaccination (ex: smallpox, rabies)
measles (rubeola)
MOST TRANSMISSIBLE DISEASE… often affects susceptible children as an acute/highly infectious/often epidemic disease caused by a paramyxovirus– negative strand RNA virus (class V)… virus enters nose and throat by airborne transmission…. used to be a common childhood illness but now it occurs only in rather isolated outbreaks (decline is due to widespread immunization programs that began in mid 1960s)… proof of immunization is required for enrollment in US public schools
rubella (german measles)
caused by positive strand RNA virus (class IV) of togavirus group… disease symptoms resemble measles but are generally milder and less contagious… routine childhood immunization is practiced in US
mumps
caused by paramyxovirus (like Measles)… highly infectious with occasional outbreaks occurring on college campuses over past 10 years… spread by airborne droplets… characterized by INFLAMMATION OF SALIVARY GLANDS… cured with host antibiotics
chicken pox (varicella) and shingles
common childhood disease characterized by a systemic papular rash… caused by VARICELLA-ZOSTER VIRUS (VZV)– a herpes virus… VZV is highly contagious and is transmitted by infectious droplets… vaccine is currently used in US… VZV establishes a lifelong latent infection in nerve cells – virus occasionally migrates to skin surface, causing a painful skin eruption (SHINGLES)
colds
most common of infectious diseases… viral infections transmitted via airborne droplets… infections are usually of short duration… symptoms milder than those of other respiratory diseases… symptoms include RHINITIS, nasal obstruction, watery nasal discharges, and malaise
common cold
commonly caused by RHINOVIRUSES– positive sense, single stranded RNA viruses (does not cause fever) (nearly 115 different strains identified)… approximately 15% of colds are due to CORONAVIRUSES (alpha primarily, some beta)… approximately 10% of colds are due to other viruses (like adnoviruses, which have fever symptoms)
influenza
caused by a RNA virus of the orthomyxovrius group… types: A, B, C (with Influenza A being the most important human pathogen)…. subtype range: hemagglutinin (H1-H16) is needed to get into cells and neuraminidase (N1-N9) is needed to get out of cell… H1-H3 and N1-N2 affects humans
influenza A
highest severity… has animal reservoirs… has 8 genome segments… pandemic population spread…. shift/drift antigenic variation… can be identified by HA + NA surface glycoproteins
influenza B
intermediate severity… no animal reservoirs… 8 genome segments… epidemic population spread… drift antigenic variation
influenza C
lowest severity… no animal reservoir… 7 genome segments… sporadic population spread… drift antigenic variation
Staphylococcus aureus
nonsporulating, gram-positive coccus that divides into several planes to form irregular clumps… causes diseases including acne, boils, pimples, impetigo, pneumoniae, osteomyelitis, carditis, meningitis, and arthritis… many diseases result from pyogenic or pus-forming, infectious or from actions of of staphylococci superantigen exotoxins… pus formation is due to production of leukocidin… is the leading cause of wound infections
helicobacter pylori
epsilon proteobacteria… gram negative, highly motile, spiral shaped bacterium associated with gastritis, ulcers, and gastric cancers… growth is inhibited by pepto-bismol (containing bismuth)… colonizes the non-acid secreting mucosa of stomach and upper intestinal tract… transmitted via person-to-person contact or ingestion of contaminated food/water
hepatitis
LIVER inflammation caused by viruses or bacteria… sometimes results in acute illness followed by destruction of liver anatomy and cells (CIRRHOSIS)… restricted group of viruses is associated with liver diseases… types: A, B, C, D, E… vaccines are available for hepatitis A and B viruses but not for other forms
hepatitis A
INFECTIOUS HEPATITIS… FROM CONTAMINATED FOOD… causes mild or rarely severe cases of liver disease
hepatitis B
SERUM HEPATITIS… “bloodborne” hepatitis… causes acute, often severe disease that can lead to liver failure and death… has vaccine
hepatitis C
produces a mild disease initially, but most individuals develop chronic hepatitis that can lead to chronic liver disease… the worst, the “silent killer”… no vaccine
hepatitis D
DEFECTIVE virus that cannot replicate and express a complete virus unless the cell is also infected with hepatitis B
hepatitis E
causes an acute, self-limiting hepatitis that varies in severity
ebola hemorrhagic fever
caused by a filovirus– negative strand RNA virus… transmitted via DIRECT CONTACT with body fluids… major reservoir is likely bats… spread controlled by universal precautions and use of personal protective equipment (PPE)
sexually transmitted infections (STIs)
aka sexually transmitted diseases (STDs)… caused by a variety of bacteria/viruses/protists/fungi… pathogens are generally only found in body fluids from the genitourinary tract that are exchanged during sexual activity
gonorrhea
caused by NEISSERIA GONORRHOEAE (gram negative diplococci)… symptoms in females: characterized by a mild vaginitis that often goes unnoticed; untreated it can lead to PELVIC INFLAMMATORY DISEASE… symptoms in males: characterized by a painful infection of urethral canal… prevalent and often asymptomatic in women
syphillis
caused by Treponema pallidum (SPIROCHETE) often transmitted at same time as gonorrhea… T. pallidum can be transmitted from an infected women to fetus during pregnancy (congenital)… three stages: PRIMARY (open lesion), SECONDARY (rash), and TERTIARY (gumas)… penicillin is highly effective for treating primary/secondary stages… low prevalence and exhibits very obvious symptoms
chlamydia
LEADING CAUSE OF STIs/STDs… chlamydia trachomatis causes a number of sexually transmitted diseases: nongonococcal urethritis (NGU) and lymphogranuloma venereum (LGV)… can lead to acute complications… elementary bodies = infectious forms
herpes simplex 1 virus (HSV-1)
infects the epithelial cells around mouth and lips… causes cold sores (FEVER BLISTERS)… may occasionally affect other body sites… spread via direct contact or through saliva… lesions heal without treatment in 2-3 weeks
herpes simplex 2 virus (HSV-2)
infections are associated with primarily with anogenital region… causes painful blisters on penis of male and cervix/vulva/vagina of females… typically transmitted through sexual contact and most easily transmitted when active blisters are present… genital herpes are currently incurable, however a limited number of drugs are successful in controlling the infectious blister stage
human papillomavirus (HPV)
causes several different infections: many infections are asymptomatic but some progress to genital warts, can cause cervical neoplasia and a few progress to cervical cancers… THERE IS AN EFFECTIVE HPV VIRUS
AIDS
recognized as distinct disease in 1981… human immunodeficiency virus (HIV) is causative agent
HIV
kills immune system by deprivation of helper T cells… as many as 1.1 million people may be infected in US, and worldwide nearly 80 million people have been infected and about 34 million have died
CD4 molecule
cell surface protein that allows HIV to infect cell
HIV treatment
four classes of drugs delay symptoms of AIDS and prolong the life of those infected with HIV: NUCLEOSIDE REVERSE TRANSCRIPTASE INHIBITORS, NON-NUCLEOSIDE REVERSE TRANSCRIPTASE INHIBITORS, PROTEASE INHIBITORS, FUSION INHIBITORS… highly active anti-retroviral therapy (HAART) is used but is often too expensive for use in developing countries which are hit hardest by HIV/AIDS
zoonosis
animal disease transmissible to humans… generally transmitted via direct contact, aerosols, or bites
enzootic
present endemically in certain populations
epizootic
incidences reaching epidemic proportions in certain populations
rabies
epizootic disease in animals but can be spread as a zoonotic disease to humans and can spread from wild animals to pets and from infected pets to humans… reservoirs in US are raccoons, SKUNKS, coyotes, foxes, and BATS (BATS and SKUNKS are major reservoirs in MI)… over 50,000 people die annually (primarily in developing countries)… over one million people receive post-exposure prophylactic care each year
symptoms and pathology of rabies
RHAABDOVIRUS– negative strand RNA virus that causes rabies; infects central nervous system of warm-blooded animals… leads to death if not treated (can get vaccination before infection causes harm due to its slow progression)… enters body through a wound or bite… in humans, NINE MONTHS may pass before onset of symptoms… virus proliferates in brain and leads to fever, excitation, dilation of pupils, excessive salivation, anxiety, and fear of swallowing
hantaviruses
cause: hentavirus pulmonary syndrome (HPS) and hemorrhagic fever with renal syndrome (HFRS)… both syndromes caused by hantavirus-infected rodents (most commonly transmitted by inhalation of virus-contaminated rodent excretion (feces))… named for Hantaan, Korea where virus was first recognized as a human pathogen… significant outbreaks have occurred in US: Yosemite camp sites in 2012 and Arizona/Colorado/New Mexico in 1993
rickettsias
small, alpha-proteobacteria that have strict obligate intracellular existence in vertebrates… associated with blood-sucking arthropods… three types: TYPHUS, SPOTTED FEVER, and EHRLICHIOSIS… CLOSELY RELATED TO HUMAN MITOCHONDRIA… contain minimal sets of genes required for intracellular dependency
typhus group: rickettsia prowazelcii
transmitted by BODY OR HEAD LOUSE bite that gets contaminated with louse feces
spotted fever group: rickettsia rickettsia
causes ROCKY MOUNTAIN SPOTTED FEVER… transmitted by DOG AND WOOD TICKS (biological vector)… over 2000 people acquire the disease every year… rickettsia grow in nucleus and cytoplasm… symptoms: headache, fever, and rash
Ehrlichiosis and tickborne anaplasmosis
emerging diseases are human granulocytic anaplasmosis (HGA) and human monocytic ehrlichiosis (HME), which are spread by tick bites)… flu-like symptoms include fever, headache, malaise, and leukopenia or thrombocytopenia… treatment with antibiotics is usually successful… avoiding hosts and using insect repellants are best measures for reducing chances of exposure
Q fever
Q STANDS FOR “QUERY”… (influenza like symptoms progress to) pneumonia like symptoms, which are caused by Coxiella burnetii, an intracellular pathogen… transmitted through contact with animals or their products (contaminated WOOL or MEAT or MILK)…. treated with tetracycline… considered a potential bioweapon
Lyme Disease
affects humans and other animals… cases were first recognized in Old Lyme, Connecticut… MOST PREVALENT TICK-BORNE DISEASE IN US… caused by spirochete BORRELIA BURGDORFERI… symptoms are closely related to symptoms of chronic syphillis… characterized by “bullseye rash”
yellow fever
caused by yellow fever virus– virus related to Dengue virus, West Nile virus, and encephalitis viruses; transmitted by mosquito bites… endemic disease of tropical and subtropical climates… found in Latin America and Africa… no antiviral drugs are effective… preventable by vaccination
dengue fever
caused by dengue virus– transmitted by mosquito bites… endemic disease of tropical and subtropical climates… found in Mexico, Latin America, India, Indonesia, and Africa… most infected individuals improve on their own… no antiviral drugs are effective… no vaccine
Zika and Chikungunya disease
in 2015 Zika appeared in Brazil and has spread throughout South America– Zika can be transmitted form mother to fetus and seems to cause severe neurological problems in the developing embryo (microcephaly or pathological small head)… both Zika and Chikungunya are considered relatively mild diseases carried by MOSQUITOS… symptoms include headache, fever, and general malaise
West Nile Virus (WNV)
transmitted by mosquito bites… transmission is seasonal… at least 130 species of birds are reservoirs… tend to not be properly identified because symptoms are subacute… no real treatment
plague
caused more human deaths than any other infectious disease (except malaria and tuberculosis)… caused by Yersinia pestis– gram negative, facultatively aerobic, rod shaped bacterium… fleas are intermediate hosts and vectors that spread it between mammalian hosts… murine toxin is the Yersinia pestis exotoxin that is a respiratory inhibitor and lethal to mice… endemic in ground rodent populations
plague
caused more human deaths than any other infectious disease (except malaria and tuberculosis)… caused by Yersinia pestis– gram negative, facultatively aerobic, rod shaped bacterium… fleas are intermediate hosts and vectors that spread it between mammalian hosts… murine toxin is the Yersinia pestis exotoxin that is a respiratory inhibitor and lethal to mice… endemic in ground rodent populations… most common form is bubonic (because of buboes that develop in infected individual)
sylvatic plague
enzootic among rodents
pneumonic plague
occurs when Yersinia pestis reaches the lungs
septicemic plague
rapid spread of Yersinia pestis throughout the body… buboes erupt inside body and infects blood
anthrax
caused by Bacillus anthracis– endospores enhance ability to disseminate B.anthracis (natural reservoir in soils, primarily associated with farm animals)… forms: cutaneous (most common form), gastrointestinal, and pulmonary
tetanus
serious/often life threatening disease… caused by an exotoxin produced by CLOSTRIDIUM TETANI… natural reservoir is soils… C.tetani gains access to body through soil contaminated wound… result of C.tetani infection on people is LOCKJAW… paralysis extends to rest of body… is preventable because the existing vaccine is completely effective… inadequately immunized individuals are at risk
gas gangrene
tissue destruction due to proteolysis and gas-producing clostridia… clostridia enter deep tissue through trauma… mainly caused by CLOSTRIDIUM PERFRINGENS… found in soil and intestinal tract of mammals… treatment with antibiotics and HYPERBARIC OXYGEN… AMPUTATION of dead tissue may be necessary
eradication of certain diseases is nearly impossible
because we cannot control/immunize all vector and reservoir animals or eradicate organisms completely from soil
common sources of waterborne disease transmission
potable water used for drinking and cooking (undergoes extensive treatment, including filtration and chlorination)… recreational water from public ponds, lakes, swimming pools, etc
most important potential common source of infectious disease is
water
indicator organism
presence indicates potential for disease… ex: coliforms (fecal coliforms, such as E.coli, used in water safety testing)– coliforms indicates fecal contamination (as do fecal streptococci)
common methods for enumerating water samples
MOST PROBABLE NUMBER (MPN) PROCEDURE, MEMBRANE FILTER (MF) PROCEDURE
cholera
severe diarrhea (death by dehydration)… caused by Vibrio cholerae (primarily infects small intestine)… typically transmitted through ingestion of contaminated water… largely restricted to developing countries (endemic in Africa, Southeast Asia, Indian subcontinent, and Central and South America)… can be controlled by application of water treatment // diagnosis, treatment, and prevention: presence of V.cholerae bacilli in “RICE WATER” STOOLS of patients is key diagnostic test; placement on CHOLERA COT; oral rehydration and electrolyte replacement therapy; individuals traveling to Cholera-endemic regions should avoid drinking water, ice, brushing teeth with tap water, and shellfish
legionellosis
pathogen of amoeba… normally transmitted in aerosols… gram-negative bacterium– its complex nutritional requirements have led to multiple methods to identify this microbe, including fluorescence microscopy; common in terrestrial and aquatic habitats… relatively resistant to heat and chlorination… legionella pneumophilis is generally transmitted by contaminated water in coolers, pools, domestic water systems
typhoid fever
the most important pathogenic bacteria transmitted by water are Salmonella enterica serovar typhi and vibrio cholera… SALMONELLA ENTERICA SEROVAR TYPHI causes typhoid fever and has been virtually eliminated in developed countries as a result of water treatment
norovirus illness
common cause of gastrointestinal illness– symptoms are vomiting, diarrhea, and malaise… transmitted by fecal oral route– most cases are traced in contaminated drinking/recreational water… often cause of mass common source outbreaks on cruise ships and in care facilities… viruses can survive in water for relatively long periods but are inactivated by disinfection with chlorine
food spoilage
any change in appearance, smell, or taste of food product that makes it unpalatable to consumer… the food’s chemical composition, physical characteristics, and water content determines its susceptibility to microbial spoilage
perishable foods
typically have higher moisture content and must be stored in conditions to limit microbial growth
semiperishable foods
foods include foods like fresh fruits and vegetables that must also be stored with care to limit microbial growth
nonperishable foods
have low moisture content and have a much longer shelf life
food preservation
slow growth of spoilage microbes… methods include: refrigeration, freezing, heating, drying and dehydration
refrigeration
slows microbial growth rate and delays spoilage
freezing
allows for longer storage but isn’t suitable for all foods
heating
used to reduce bacterial load (PASTEURIZATION) of a product or to actually sterilize it (CANNING)
drying and dehydration
moisture content (water activity) is critical for microbial metabolic processing– adding sugar or salt reduce water availability for microbial growth
fermentation
anaerobic catabolism of organic compounds (generally carbohydrates)… important bacteria: lactic acid bacteria, propionic acid bacteria, and acetic acid bacteria… products include yeast bread, cheese, yogurt, buttermilk, sausage, sauerkraut, and soy sauce
food poisoning (aka food intoxication)
disease that results from ingestion of foods containing preformed microbial toxins… microorganisms that produced toxins do not have to grow in host
food infection
microbial infection resulting from ingestion of pathogen-contaminated food followed by growth of pathogen in host
staphylococcal food poisoning
food poisoning is often caused by toxins produced by Staphylococcus aureus– it can grow on common foods and some strains produce heat-stable enterotoxins… gastroenteritis occurs within a few hours of consumption… estimated that 185,000 cases of staphylococcal food poisoning occurs each year… enterotoxins of S.aureus classified as superantigens produce large T cell response and an inflammatory response
clostridial food poisoning
clostridium perfingens and clostridium botulinum cause serious food poisoning– produce endospores that may not be killed during cooking or canning process (home-canned vegetables cause most common source individual food borne botulism outbreaks)… C. perfingens is most commonly reported form of food poisoning (248,000 annual cases)– large numbers of cells (>10^8) must be ingested; enterotoxin is produced in intestinal tract six to fifteen hours after consumption
botulism
severe and often fatal food poisoning… caused by exotoxin produced by CLOSTRIDIUM BOTULINUM– botulinum toxin is a neurotoxin but is destroyed by heat… average of 110 cases annually (45% infant cases, 30% wound cases, and 25% foodborne cases)…. home prepared foods are a common source of illness
Salmonellosis
gastrointestinal illness caused by foodborne Salmonella infection… caused by eating food contaminated with Salmonella or handling Salmonella-infected animals (birds/reptiles)… onset of disease occurs 8-48 hours after ingestion… disease normally resolves in 2-5 days… Salmonella ingested in food or water evades phagocytes and grows as an intracellular pathogen
pathogenic Escherichia coli
intestinal parasites and a few produce potent enterotoxins… Shiga toxin producing E.coli (STEC) including 0157:H7 produces verotoxin – causes bloody diarrhea and kidney failure… other types of E. coli are enterotoxigenic (ETEC), enteroinvasive (EIEC), and enteropathogenic (EPEC)
campylobacter
common cause of bacterial foodborne infections in US– more than 2 million cases of bacterial diarrhea per year… transmitted to humans via contaminated food (raw poultry, pork, raw shellfish, or in surface waters)… replicates in small intestine… causes high fever, headache, malaise, nausea, abdominal cramps, and bloody stools
listeriosis
caused by listeria monocytogenes– intracellular pathogen and is PSYCHROTOLERANT (likes to grow in fridge)… may lead to bacteremia and meningitis… no food product is safe from contamination… uptake of pathogen by phagocytes results in growth and proliferation of bacterium (used actin for movement in cell)… mortality rate is 16%, particularly in pregnant women and fetuses
largest numbers of annual foodborne infections are thought to be caused by
viruses
enteroviruses
shed into food/water from feces… examples: poliovirus, norovirus, and HEPATITIS A (and hepatitis E)
noroviruses
responsible for most infections
noroviruses
responsible for most infections
ROTAVIRUS, hepatitis A, and astrovirus
responsible for the rest of infections
protists
important foodborne diseases are caused by GIARDIA INTESTINALIS, CRYPTOSPORIDIUM PARVUM, and TOXOPLASMA GONDII… can be spread in foods contaminated by fecal matter in water used to wash, irrigate, or spray crops… fresh fruits are often the source of these infections… toxoplasma gondii can be spread by raw or undercooked meat
prions
proteins that adopt NOVEL CONFORMATIONS that inhibit normal protein function and cause degeneration of neural tissue… variant CREUTZFELDT-JAKOB DISEASE (vCJD)– linked to consumption of meat from cattle suffering with BOVINE SPONGIFORM ENCEPHALOPAHTY (BSE)
pathogenic fungi
only about 50 fungal species cause disease– fungi can be single celled YEASTS or hyphae-forming MOLDS, while some are DIMORPHIC (meaning they can be either molds or yeasts)
major mechanisms through which fungi cause disease
ALLERGIC RESPONSES to fungi… MYCOTOXINS (eg AFLATOXINS)… INFECTIONS (MYCOSES)– superficial, subcutaneous, systemic
superficial mycoses
caused by dermatophytes or fungus living in skin… most common causative agent is TRICHOPHYTON… fungi colonize hair/skin/nails and infect only the surface layers… example: athlete’s foot
subcutaneous mycoses
situations where fungi colonize deeper layers of skin tend to be more serious than superficial fungal infections… different groups of fungi may cause subcutaneous infection: SPOROTHRIX, FONSECAEA, and CLADOSPORIUM
systemic mycoses
most serious types of fungal infections… humans become infected by inhaling spores, where fungal growth then occurs in internal organs of body… examples: HISTOPLASMOSIS (caused by Histoplasma capsulation); COCCIDIODOMYCOSIS (caused by Coccidiordes immitis); BLASTOMYCOSIS (caused by Blastomyces dermatidis); PARACOCCIDIOIDOMYCOSIS (caused by paracoccidiodes brasiliensis); CRYPTOCOCCOSIS (caused by Cryptococcus neoformans)
pre-disposing conditions for fungal infections
impaired immune system or those taking immunosuppressive drugs (ex: AIDS patients)… pregnant women (weakened cellular immune response)… very young and very old individuals (weakened cellular immune response)… antibiotic users (normal microbiota is disrupted)
entamoeba histolytica
pathogenic protist transmitted to humans primarily through contaminated water and sometimes food… anaerobic and produces resistant cysts… infection can be asymptomatic or lead to diarrhea and/or DYSENTRY (bloody/pus-y diarrhea)
naegleria fowleri
free living amoeba found in soil and water runoff that can also cause amebiasis… infections usually result from swimming in warm, soil-contaminated natural water sources (hot springs or lakes)… enters human body through nose and burrows directly into brain, causing extensive hemorrhage and brain damage (MENINGOENCEPHALITIS)
balantidium coli
CILIATED intestinal human and swine parasite… infections caused by cysts… transmitted to humans through fecally contaminated water… symptoms resemble those of amebiasis
giardia intestinalis
flagellated anaerobic parasite… has mitosomes… produces highly resistant cysts (cysts are capable of withstanding chemical disinfection)… cause of giardiasis, a common waterborne disease… symptoms: explosive, foul-smelling diarrhea, intestinal cramps, nausea, weight loss, and malaise… many individuals exhibit no symptoms and can act as carriers
trichomonas vaginalis
flagellated anaerobic parasite… transmitted person-to-person by sexual intercourse… no cyst form… can survive on moist surface (can be transmitted by toilet seats, sauna benches, and towels)… vaginal discharge, itching, and burning in women
cryptosporidium parvum
protist that lives as a parasite in warm-blooded animals… produces thick-walled cells (oocysts) that are shed in the feces of infected animals… oocysts are transmitted in fecally contaminated water…. oocysts are highly resistant to chlorine and UV radiation, thus sedimentation and filtration methods are most effective at removal
toxoplasma gondii
protist that lives as a parasite in warm-blooded animals… produces oocysts that are shed in feces of infected animals… oocysts are transmitted by cats or undercooked meat… toxoplasmosis is mainly asymptomatic, but can damage eyes/brain/other organs in immune-compromised individuals and/or birth defects… humans are incidental hosts, so infected humans do not transmit disease… can change host behaviour to encourage dispersal
malaria
protist disease caused by PLASMODIUM spp… has a complex life cycle that includes Anopheles mosquitoes as biological vectors… most common cause of death due to infectious disease worldwide (estimates 350 million infected people and over 1 million deaths annually)… generally found in tropical and subtropical regions… diagnosis requires identifying plasmodium-infected erythrocytes in blood smears… drugs are used to prevent and treat infections (CHLOROQUINE and primaquine)… contained by reducing population of mosquito vector
Leishmaniasis- Leishmania tropica or Leishmania mexicana
flagellated protozoan… related to Trypanesoma… causes cutaneous leishmaniasis… transmited by bite of sandfly (insect vector)… infects and grows in macrophages… forms nodules and ulcers on skin… treatment with antimony compounds
Leishmaniasis- Leishmania donovani
causes visceral leishmaniasis… transmitted by bite of sandfly (insect vector)… parasite travels to internal organs… damage to liver, spleen, and bone marrow… if untreated, visceral disease is fatal… treatment includes antimony compounds, bed rest, and blood transfusions
Trypanosomiasis- Trypanosoma brucei
two subspecies: T. brucei gambiense and T. brucei rhodesiense… causes AFRICAN SLEEPING SICKNESS… transmitted by bite of tsetse fly (insect vector)… parasite multiplies in blood… infects central nervous system and multiplies in spinal fluid… treatment includes anti-trypanosomal drugs
Trypanosomiasis- Trypanosoma cruzi
causes CHAGA’S DISEASE (american)… transmitted by bite of “kissing bug” (insect vector)… parasite affects heart, gastrointestinal tract, and central nervous system… occurs in Latin American countries
schistosomiasis
aka snail fever… caused by trematode Schistosoma… eggs released into freshwater -> eggs become miricidia -> miricidia infect snails and become cercaria -> cercaria burrow into skin, leaving skin lesions… occurs in tropical/subtropical countries
filariases
transmitted by bite of mosquito (insect vector)… called BANCROFT’s FILARIASIS (“elephantiasis”)… caused by nematode WUCHERERIA BANCROFTI… worms interrupt lymph flow… chronic infection of lymphatic system… causes massive enlargement of legs
trichinosis
caused by nematode Trichinella spiralis… worm lives in muscle tissue of wild mammals… worm infects pigs -> humans eat undercooked meat -> larvae enter intestinal mucosa -> larvae can circulate throughout body
