WEEK 4: PARASITES AND PARASITIC INFECTIONS Flashcards
What is a parasite?
- Organism which lives UPON or WITHIN another living organism (the host) at whose expense the parasite obtains some advantage
What are 2 advantages for a parasite?
Provision of nutrients (essential)
Protection from environment, host immune system etc.
What is one disadvantage for parasites?
Host controls and regulates parasite growth and development (host immune system)
What factors are host-parasite relationships affected by? (3)
- Social and economic
- Environmental
- Travel and human migration/population movement
What are the 6 different types of organisms that parasitic diseases can be caused by?
- Viruses
- Bacteria–> Chlaymdia trachomatis-STD and eye disease
- Fungi/Yeast and Algae –>Candida albicans
- Protozoa –> unicellular
- Helminths
- Arthropods
What are the two different types of parasites?
- Ectoparasite and endoparasite
What is an ectoparasite?
- An organism that lives on the surface of its host e.g. mosquitos tse tse flies as vectors of transmission
What is an endoparasite?
- Parasitic organism that lives within the host
What are the common features of eukaryotic cells?
- Membrane delimited nuclei
- Membrane bound organelles that perform SPECIFIC functions
- Intracytoplasmic membrane complex serves as transport system
MORE STRUCUTRALLY COMPLEX and larger thana bacterial and archaeal cells
What does a fungal yeast cell (eukaryotic) contain that a human eukaryotic cell doesn’t?
- Bud scar and storage vacuole
What does a protoozan cell (eukaryotic) contain that a human eukaryotic cell doesn’t?
- Water vacuole
Are fungi eukaryotes or prokaryotes?
- Eukaryotes
Do fungi contain cell walls?
- Yes
Do fungi have typical eukaryotic organelles?-
- Yes
Do fungi contain unicellular (for yeast) and or multicellular filaments? (If so, what are these known as?_
- YES!
- Known as hyphae or mycelia)
How many cells do the spores produced by fungi in the sexual or a sexual life cycles give rise to?
- Gives rise to MULTIPLE cells (unlike bacteria)
What role to fungi normally play?
- Play role in the decomposition of organic material
Are fungi mostly non pathogenic?A
- Yes , only 300 linked to disease
What is the most common plant pathogen (general)?
- Fungi
What are human mycoses caused by?
- TRUE fungal pathogens and opportunistic pathogens
What is the most common fungi that causes Candidias?
- Candidia albicans
Where does Candidia normally reside?
- The intestinal tract and can be found on mucous membranes and skin
What causes the symptoms of Candidia to devleop?
- Overgrowth of Candidia albicans organisms
What is a vulvovaginal yeast infection?
- Panful infalmmatory condition of the genital region that causes ulceration and whitish discharge
Where does cutaneous candidiasis occur?
- In chronically moist areas of skin and also in burn patients
Is Candida auris contagious?
- YES!
- It is spread from person-person or from fomite contamination
What is the treatment for Candidiasis?
- There is NO SATISFACTORY TREATMENT BUT
- antifungals are used for cutaneous lesions and systemic candidiasis
Are most protists unicellular or multicellular?
- Most are UNICELLULAR
Are protists prokaryotic or eukaryotic?
- Eukaryotic
Are protists polyphyletic?
- YES–> derived from more than one common ancestor
What is the distribution of protists?
- Grow in MOIST habitats
- Free living
- Chemo-organotrophic forms play role in recycling N and P
- Terrestrial and planktonic forms
- Parasitic forms in humans and dogs
Which areas of the body can protists infect?
- ALL major tissues and organs
How do extracellualr protists evade the immune system?
- Evade the recognition of their plasma membrane
- e.g. trypanosomes undergo antigenic variation of surface antigens
- Mlaria has polygenic vairation
How do intracellular protists evade the immune system?-
- They ‘hide’ inside a host cell
- e.g. Leishmania evades harmful effects of reactie O2 species in phagolysosome
What are the 4 infection routes?
- Via an intermediate host (Accidental ingestion of larvae in tissue of another host e.g. pork meat)
- Via fecal-oral route (accidental ingestion of larvae or eggs from faeces of infected host)
- Active skin penetration (larval stages invade through skin-hookworm?)
- Injection by blood-sucking insect (Larval stages develop to infectivity in insect intermediate host)
Can there be parasitic infections transmitted from mother to fetus?
- YES
What are most parasitic infections acquired through?
- Contaminated water, food or via insect vectors
Are protozoa single celled eukaryotes?
- YES
What is an example of a protozoa that is an oprotunistic pathogen?
- Cryptosporidium
What are zoonoses and some examples?
- Animal diseases transmissible to humans that can be transferred by DIRECT or INDIRECT methods
- E.g. Parasites–> Cryptosporidium, Giardia, Leishmania, Toxoplamsa, Plasmodium, Taenia solium (pork tapeworm), Rabies
What percentage of pathogens known to infect humans are zoonotic?
- 70%
What does the excavata class contain and what is the main example?
- Excavated feeding groove on side of cell body
- NO plasitds no mitochondria
- Main example = Giardia
What is Giardiasis caused by (organism)?
- Giardia lambila
What are 6 potential causes of Giardiasis?
swollowing it from picking it up from surfaces that contain faeces from an infected person or animal
- Drinking water or ice made from water sources where giardia may live
- Swallowing water while swimming or playing in water where giardia could be present
- Eating uncooked food that contains Giardia organisms
- Having contact with someone who is ill with giardiasis
- travelling to countries where giardiasis is endemic
What are the two life forms (cycles) that Giardia lambila is in?
- The RESISTANT cyst stage
- the VEGATATIVE trophozoite stage
What is the incubation period for Giardiasis?
- 4-25 days
What is the reservoir of infection for Giardasis?
- humans and animals
In what period of time should tests be done for Giardiasis and WHY?
-3 day period because excretion of many many cysts occurs in ‘showers’
What are some of the symptoms of Giaridasis?
- Diarrhea
- Gas
- Flatulence
- Greasy stool
- Abdominal cramps
- Nausea
- Weight loss
Do all people with Giardiasis have symptoms?
- NO
What is the pathogenesis of Giardiasis?
- In duodenum they undergo developmental change and form TROPHOZOITES
- TROPHOZOITES attach to duodenal epithelial cells via SUCKING DISK (very hard to remove)
- FEED on mucosal secretions and grow and multiply, interfering with intestinal absorption –> Abdominal pain, diarrhea etc.
- Can be ACTUE or CHRONIC (6-8wks or longer)
Is it possible to become infected with giardia through contact of blood?
- NO!
What is the protozoa class of Apicomplexa and what is an example?
- A large group of eukaryotic protists that contain an APICOPLAST (reliced chloroplast organelee)
- And an apical complex structure involved in penetrating host cell
- e.g. Cryptosporidium (coccidia) and plasmodium (haemosporidia)
What is cryptosporidius caused by?
-Apicomplexan protozoan –> Cryptosporidium parvum
What can cryptosporidius contaminate?
- Reservoirs and swimming pools
What is the incubation period for cryptosporidius?
- 2-14 days
What are the symptoms of Crytosporidius?
- Persistent pain, vomiting, diarrhoea
How is cryptosporidius spread?
- Faecal-oral route
- Consumption of faecal contaminated food or water
Where is the SEXUAL CYCLE in cryptosproidiosis?
- In the vertebrae host (NO INSECT VECTOR)
- Complex life cycle in SINGLE HOST OOCYST and a trophozoite stage
- It produces oocytes that are RESISTANT to chlorination BUT killed by conventional cooking or boiling
What is resistant to chlorine?
- The cysts that cryptosporidium produces
Is there a potenital drug treatment for Cryptosporidiosis?
- Yes
- Nitazoxanide
Are the oocytes that are resistant to chlorine resistant to boiling/cooking?
- NO! They can be killed from cooking or boiling
What is the right preventive measures to take from Cryptosporidium and what should be done if someone has it?
- People who are infected should be excluded from childcare, school and work until there has been no diarrhoea for 24 hours (people should not use the pool for 14 days after diarrhoea)
- Prevention by pasteurisation and boiling + washing hands
What type of parasite is malaria caused from?
-Caused by PROTOZOAN parasites of Plasmodium genus (P. falciparum, P.vivax, P.ovale, P.malariae, P.knowlesi
What is the class Apicomplexa specialised for?
-Invasion and intracellular growth (liver and RBCs for malaria
Is there an effective vaccine for malaria?
NO
What is the most widespread and dangerous of the 4 species of plasmodium?
-Plasmodium falciparum
What is the transmission of Plasmodium and why?
- Form person-person via the FEMALE ANOPHELES MOSQUITO
- Males DO NOT transmit disease feed on plant juices
What are the two stages of reproduction in plasmodium?
- Sexual
2. Asexual
Where does the sexual life cycle stage of plasmodium occur?
- In the Anopheles mosquito
Where does the asexual life cycle stage of plasmodium occur and what happens?
- In the HUMAN -called sporozoans –> these MULTIPLY and produce merozoites –> these become trophozoits
What is the infection cycle (basic) for plasmodium to cause malaria?
- Plasmodium develops in the gut of mosquito and is passed on in saliva of infected insect
- Mosquito bite occurs
- Sporozoits are carried by blood to victims liver where they form cyst-like strucutre containing THOUSANDS or merozoites
- After 9-16 days, they RETURN to blood and PENETRATE red cells where they multiply again, progressively breaking down the RBCs (hemolysis)
- This induces BOUTS of FEVER and anaemia in infected individual
What occurs in cerebral malaria and what is the result?
- Infected Red cells OBSTRUCT the blood vessels in brain
- Other vital organs can also be damaged leading to death of the patient
What is a potential treatment for malaria?
-Using a naturally occurring fungus and bacteria to kill mosquitos before they can transmit the disease
What is toxoplasmosis caused by?
-Protozoan parasite (Apicomplexa)–> Toxoplasmosa gondii (T.gondii)
What is the primary and intermediate host of toxoplasmosis?
- PRIMARY HOST (where the adult/mature (sexual) form of parasite occurs) = CATS!! Where the parasites replicate in the gut –> produce oocysts–> and spread in faeces
- INTERMEDIATE HOST= Humans, pig, sheep, dogs, goat, chicken, beef, birds
How is toxoplasmosis transmitted?
- Ingestion of RAW/undercooked cyst-infected meat
- Contaminated drinking water
- Ingestion of raw/undercooked vegetables
- Ingestion of cat faeces (kids sandpits)
- Transplacental transmission of active zooites
What occurs in toxoplasmosis in normal people that get it?
- Acute INFLAMMATORY RESPONSE (clinically unapparent)
- Muscle aches and pains
- Swollen lymph glands
- Gi involvement
- Symptoms resolve QUICKLY but result in chronic infection formation of cysts (or may not be symptomatic depending on location of cysts-eye or brain)
What occurs in toxoplasmosis in people who are immunocompromised or pregnant?
- Severe and serious pathological consequences
- Immunocompromised people (HIV) Severe toxoplasmosis involving gut, eye, heat, brain and other ORGAN DAMAGE
- Pregnant women–> congenital toxoplasmosis –>foetal ABNORMALITIES (eye, brain–> encephalitis (larger brain) , jaundice)
- Can develop from ACUTE infection or reactivation of cysts after infection EARLIER in life
What can toxoplasmosis be misidentified as?
Parkinsons
Can T.gondii affect behaviour?
- YES! Possibly as a parasitic survival tactic to spread from host-host
- Linked to (possibly) a parasite (cyst) encoded tyrosine hydroxylase that MIMICS DOPAMINE possibly modifies behaviour
What is the diagnosis for toxoplasmosis?
- Serology (ELISA for anti-toxoplasma serum Igs) blood test
- PCR
- Histology (detection of tissue cysts) or gross pathology (retina)
- Hard to determine whether the infection is ACTUTE or CHRONIC
Is there usually treatment for normal people who have toxoplasmosis?
- NO
Is there usually treatment for immunocompromised or pregnant people?
- Antibiotics
What is the prevention for Toxoplasmosis? (6 things)
- Wear gloves when gardening, careful cleaning cat litter trays
- Don’t get too close to your cat
- Wash hands PROPERLY
- Cook all meat THOROUGHLY
- Wash and PEEL vegetables (only in selected countries)
- Clean surfaces to prevent CROSS CONTAMINATION
Are there vaccines available for toxoplasmosis?
- NO
What is the proper name for hookworms?
- Ancylostoma duodenale
What are hookworms (Ancylostoma duodenale) the most common cause of?
- Iron defficiency
Where do hookworms live?
In small bowel attached to mucosa (for 1cm)
What symptoms do hookworms cause?
-GI infections, diarrhea, abdominal pain
What is the life cycle of hookworm?
- Eggs in faeces
- Rhabditiform larva hatches
- Faliform larva
- Faliform larva PENETRATES skin
- Adults in small intestine
What is the most common form of tapeworm?
- Taenia solium (Pork tapeworm)
What is the lifecycle of the tapeworm?
- Eggs or gravid proglottids in faeces and passed into environment
- Pigs become infected by ingesting vegetation (contaminated)
- Oncospheres hatch, penetrate intestinal wall and circulate to musculature –> oncospheres develop into cystecerci in muscle
- Humans infected by ingesting raw or undercooked infected meat
- Sucker (Scolex) attaches to intestine
- Adults form in small intestine and grow in segments
What is the largest roundworm?
-Ascaris lumbricoides that paratises the HUMAN INTESTINE, 3cm as adult
What is the life cycle of round worm?
- 2 phases; lung and intestinal
- Egg ingested–> hatches in DUODENUM –> larvae PENETRATE intestine wall, enter blood vessels and EMBOLISE through liver–> lungs
- Then MIGRATE to air spaces up trachea and swallowed –> PERMANENT ADULT RESIDENCE in small intestine (takes 2 months for worms to mature)
- Produces 200 000 eggs per day + adult worms live 1-2 years
What are the clinical symptoms of round worm related to?
- The NUMBER of worms
- Small numbers= asymptomatic
- Large nubmers= Obstruction, pains
What are the two phases of roundworm infection?
- Lung phase
2. Intestinal phase
How long after initial infection does the lung phase occur (roundworm)?
- 6-14 days
What is A.lumbricoides known as in the lung phase of a roundworm infection?
- Ascaris pneumonitis
What occurs in the lung phase of roundworm infection?
-In lung–> causes HEMORRHAGE, inflammation, bacterial infection + allergy where places have seasonal transmission
How long after initial infection does the intestinal phase occur (roundworm)?
6-8 weeks after initial exposure
What does the intestinal phase of round worm infectiom cause?
- Malnourishment and intestinal blockage
What are the 2 applications of parasites in human medicine?
- Medicinal leeches –> Decrease swelling + improve blood flow in surgery sites (skin grafts and reattachments)
- Medicinal maggots–> Clean wounds that contain DEAD tissue
Why are vaccines hard to develop for parasites?
-Because of their complex anatomy
