Chapter 21: Rickettsias, Chlamydias, Spirochetes, and Vibrios

Question 1

What are some general characteristics of family Rickettsias?

Answer 1

Extremely small like viruses, however are different because they contain DNA, RNA, ribosomes, and reproduce by binary fission

Named after Howard Ricketts

Appear almost wall-less due to small amount of peptidoglycan

Obligate intracellular parasites- unusual since they have functional genes for protein synthesis, ATP production, and reproduction, may have “leaky” cytoplasmic membrane

4 Genera- Rickettsia, Orientia, Ehrlichia, and Anaplasma

Question 2

What are some general characteristics of the Rickettsia genera?

Answer 2

Non-motile, aerobic, intracellular parasites thate live in cytosol of host cell

Hematoxylin and Eosin (H&E) staining

Pathogen grows and reproduces slowly

Enters the host cell by stimulating endocytosis

Once inside- pathogen secretes an enzyme that digests the endosome membrane, releasing bacteria into the cytosol

Question 3

What are some important general characteristics of the 3 species of Rickettsias?

Answer 3

R. rickettsii & R. typhi- continously released via exocytosis

R. prowazekii- fills up the host cells until the host cell lyses, releasing the parasites

Transmitted via arthropod vectors- different for 3 species

Question 4

What is the disease caused by Rickettsia rickettsii?

Answer 4

Rocky Mountain Spotted Fever- more severe and common rickettsial illness, rash on the wrists, ankles, soles, and plams that later spreads to trunk, petechial hemorrhages

Most prevalent in Appalachian Mountain and Oklahoma

Hard ticks (Dermacentor) transmit among humans and rodents- serve as vector, bacteria are dorment for several hours in the salivary glands of ticks

Activated bacteria released into mammalian host’s circulatory system where they proliferate in the endothelial lining of small blood vessels

About 5% of patients die

Question 5

How do you diagnose and treat Rocky Mountain Spotted Fever?

Answer 5

Diagnosis by Fab test and prevention involving avoiding ticks

Treatment- removal of ticks and doxycycline

Question 6

What is the disease caused by Rickettsia prowazekii?

Answer 6

Causes epidemic typhus (louse-borne typhus)

Human body louse transmits bacteria to humans, flying squirrels serve as reservoir

Species kills live within 2-3 weeks preventing transovarian transmission

Humans are primary host

Occurs in crowded, unsanitary conditions, endemis in Central and South America and in Africa

Question 7

What is the reoccuring disease caused by the Rickettsia prowazekii?

Answer 7

Brill-Zinsser disease

Sudden onset of fever and headache, pink macules appear on upper trunk and then cover entire body

Rash spares the palms, soles, and face

Treatment- doxycycline, tetracycline, or chloramphenicol

Prevent- good hygience, vaccine available for high risk areas

Question 8

What is the disease caused by Rickettsia typhi?

Answer 8

Causes endemic or murine typhus

Reservoir- rodents Vector- fleas

Disease is usually not fatal

Rash typically restricted to chest and abdomen

Most often in south US from FL to CA

Endemic in every continent except Antarctica

Prevent by avoiding arthropod vectors

Question 9

What is the disease caused by Orientia?

Answer 9

Originally classified in the genus Rickettsia- however, have different rRna sequence, thicker cell wall, minimal slime layer

Mites- reservoir and vector or Orientia, transmit bacteria via transovarian transmission to offspring which then spreads it among rodents and humans

Scrub typhus caused by O. tsutsugamushi

Occurs in U.S. among immigrants from endemic areas (eastern Asia, Australia, and Japan)

Characterized by fever, headache, muscle pain, less than half of the patients also develop a rash on trunk and appendages

Prevent by avoiding exposure to mites- no vaccine

Question 10

What are the characteristics and diseases caused by Ehrlichia and Anaplasma?

Answer 10

Cause two emerging disease in US:

E. chaffeensis- human monocytic ehrlichiosis

Anaplasma phagocytophilum- causes anaplasmosis

Ticks serve as vectors

Triggers its own phagocytosis by leukocytes

Grow in phagosome and prevent phagolysosomal fusion

3 developmental stages in leukocytes- Elementary bodies, initial body, and morula

Diagnosis- difficult, non specific symptoms, no rash, leukopenia

Prevent- avoid ticks

Question 11

What is the growth and reproductive cycle Ehrlickia and Anaplasma?

Answer 11

Enters cells as an elementary body

Then multiplies to form an initial body

When a cell membarne forms around clump known as a morula

Morula then released

Question 12

What are some general characteristics of Chlamydias?

Answer 12

Very small like viruses, possess DNA, RNA, and 70S ribosomes

Are non-motile but do not have cell walls- two membranes without peptidoglycan

Obligate intracellular parasites- can grow and multiply only within the vesicles of host cells

Do not have arthropods as vectors or hosts

Lack enzymes to synthesize ATP- energy parasites

Question 13

What is the developmental cycle of a chlamydia?

Answer 13

Involves 2 forms

Elementary bodies (tiny cocci, dormant infective forms and reticulate bodies (larger pleomorphic, noninfective)

Both forms can occur within the phagosome of a host cell

Prevent the fusion of phagosome and lysosome

Question 14

What are the virulence factors of Chlamydia trachomatis?

Answer 14

Has a limited host range- one strain infects mice, all others infect humans

Infects the cells that have receptors for elementary bodies- conjuctiva and various mucous membranes

Enters the body through abrasions and lacerations

Most common reportable STD in US

Clinical manifestations due to cell destruction and inflammatory response

Re-infection at same stie can result in hypersensitivity reactions leading to blindness, sterility, or sexual dysfunction

Question 15

What are the diseases caused by Chlamydia trachomatis?

Answer 15

STD- lymphogranuloma venereum

3 stages of infection

Transient genital lesions, swollen inguinal lymph nodes, Nongonococcal urethritis, proctitis

Trachoma- ocular disease, pathogen multiplies in conjunctiva and kills them, leading cause of nontraumatic blindness in humans, infection typically occurs during childbirth

Question 16

How are chlamydia trachomatis infections diagnosed, treated, and prevented?

Answer 16

Diagnosis- demonstrate bacteria inside cells from site of infection

Treatments- antibiotics for genital and ocular infection, sugical correction of deformities from trachoma may prevent blindness

Prevention- abstinence, blindness prevented with proper antibacterial agents

Question 17

What are the diseases caused by Chlamydophila pneumoniae?

Answer 17

Causes bronchitis, pneumonia, and sinusitis

Also implicated in atheroschlerosis-lipid deposits on walls of arteries

Most infections due not require hospitalization

Severe cases can resemble primary atypical pneumonia

Prevention is difficult becuase C. pneumoniae is ubiquitous

Question 18

What are the diseases caused by Chlamydophila psittaci?

Answer 18

Causes ornithosis (psittacosis, parrot fever)- disease of a bird that can be transmitted to humans

Usually causes flu-like symptoms, rarely non-respiratory conditions are observed

Transmitted via inhalation of aerosols or contact with infected material or a pet bird

Difficult diagnosis since symptoms are similar to other respiratory infections

Treatment- doxycycline for 2 weeks

No vaccine available

Question 19

What are some general characteristics of Spirochetes?

Answer 19

Thin, tightly coiled, helically shaped Gram negative bacteria

Share unique feature- presence of axial filaments(composed of endoflagella located in the periplasmic space between the cytoplasmic membrane and the outer membrane)

Moves in a corkscrew motion through its environment- allow pathogen to burrow through host tissues

3 Genera cause disease- Treponema, Borrelia, and Leptospira

Question 20

What are some general characteristics of Treponema:?

Answer 20

Pathogens of human only

T. pallidum is the most widespread

Organism difficult to visualize by regular light microscopy due to flattened helical cells- phase contract or dark field microscopy used, special stains or dyes used

Bacteria destoryed by exposure to heat, disinfectants, soap, drying, pH changes, etc.

Scientists unable to culture Treponema in cell-free media, can grow in rabbits, monkeys, and epithelial cells

Question 21

What are the virulence factors of Treponema and what disease does it cause?

Answer 21

Produce hyauronidase and glyocalyx- help in infiltrating spaces and protect ion from phagocytosis

Syphilis occurs worldwide- transmission is solely via sexual contact, endemic among sex workers, homosexuals, and users of illegal drugs

Congenital syphilis- infection spreads from the mother to the fetus, may results in fetal death or mental retardation and malformation

Diseaase occurs throughout US, particularly Southeast

Question 22

What are the four stages of syphilis?

Answer 22

Primary- starts with a painless, reddened lesion called a chancre at the site of infection 10-21 days after exposure, chancres typically form around external genitalia, but also form in mouth, anus, fingers, etc.

Secondary- starts with invasion of bacteria into bloodstream, sore throat, fever, myalgia, lymphoadenopathy, and rashes that include palms and soles of the feet

Latent phase- commences after several weeks, may last up to 30 years

Tertiary phase- last phase, inflammation and hyperimmune responses, syphilitic lesions called gummas- rubbery, painfully swollen lesions

Question 23

How is a syphilis infection diagnosed, treated, and prevented?

Answer 23

Diagnosis- antibody tests against T. pallidum, spirochetes can be observed in fresh discharge from lesions, tertiary syphilis is difficult to diagnose

Treatment- penicillin, ineffective against tertiary syphilis

Prevention- abstinence and safe sex

Question 24

What are the other types of disease caused by Treponema?

Answer 24

Nonvenereal treponemal diseases- primarily seen in impoverished children in unsanitary conditions in Africa, Asia, and South America

Bejel- T. pallidum endemicum, spread by contaminated eating utensils, oral lesions

Pinta- T. carateum, skin disease, spread by skin to skin contact

Yaws- T. pallidum pertenue, granular skin lesions

Question 25

What are some general characteristics of Borrelia?

Answer 25

Lightly staining, Gram-negative spirochetes

Cause two diseases in humans: Lyme disease and relapsing fever

Question 26

What are some characteristics of Lyme disease?

Answer 26

Causative agent- Borrelia burgdorferi

Lyme disease is characterized by: arthritis, other dermatological, cardiac, and neurologocial abnormalities, infected children may have Bell’s palsy

Borrelia is unusual in that it lacks iron-containing enzymes and proteins in its ETC, uses manganese instead

Question 27

How is Lyme disease transmitted?

Answer 27

Bacteria are transmitted to humans via a tick bite

Hard ticks of the genus Ixodes are the vectors, must remain on host for at least 48 hours

Mice and deer are animal reservoirs

Tick life cycle important in the understanding spread of Lyme disease

Question 28

What are some sign and symptoms of Lyme disease?

Answer 28

Shows a broad range of signs and symptoms

Three phases of disease in untreated patients:

Expanding red “bull’s-eye” rash occurs at infection site within 30 days

Other symptoms: fever, chills, headaches, dizziness, fatigue, joint pain, lymphadenopathy

Neurologocial symptoms and cardiac dysfunction

Severe arthritis that can last for years- result of the body’s immune response

Question 29

How is Lyme disease diagnosed?

Answer 29

Rarely though presence of bacteria in blood smears; Mostly through serological testing

Two stage testing process to measure the body’s protection of antibodies to the Lyme disease bacterium

1. Enzyme-linked immunosorbent assay (ELISA) or indirect immunofluorescence (IFA)
2. Western immunoblot of samples that tested positive or equivocal by ELISA or IFA

Question 30

How do you treat and prevent Lyme disease?

Answer 30

Treatment- antimicrobial drugs effectively treat the first stage of Lyme disease, treatment of later stages difficult because symptoms result from immune response

Prevention- avoid ticks, use DEET

Question 31

What is relapsing fever?

Answer 31

Louse-borne relapsing fever- caused by Borrelia recurrentis

Transmitted to humans by the human body louse

Tick-borne relapsing fever- caused by several Borrelia species

Transmitted to humans by soft ticks of genus Ornithodorus

Ticks and rodents are common reservoir

Characterized by recurring episodes of septicemia and fever- due to body’s repeated efforts to remove the spirochetes

Question 32

How is recurring fever diagnosed, treated, and prevented?

Answer 32

Diagnosis- observation of spirochetes

Treatment- antimicrobial drugs like doxycycline or erythromycin

Prevention- avoidance of ticks and lice, good personal hygiene, use of repellant chemicals

Question 33

What are some general characteristics of Leptospira?

Answer 33

Motile by two means of axial filaments, obligately aerobid bacteria

Found in numerous wild and domestic animals- rat, racoons, foxes, hose, cattle, and pigs

Grows in kidney tubules

Leptospirosis- caused by L. interrogans and is zoonotic in nature, named because on end of spirochete is hooked like a question mark

Question 34

How is the Leptospira infection contracted, diagnosed, treated, and prevented?

Answer 34

Humans contract disease via contact with infected urine or environment

Leptospira enters cuts/abrasion in skin and mucous membranes

Travels via the bloodstream throughout the body- infection may lead to kidney dysfunction, bacteremia eventually resolves; spirochetes found only in kidneys

Diagnosis- antibody tests

Eradication impractial due to various animal reservoirs, vaccine available for animals

Question 35

What are some general characteristics of Vibrios?

Answer 35

Share many characteristics with enteric bacteria (O polysaccharide antigens), oxidase positive

Found in water environments worldwide

Most pathogenic species can survive in shellfish

Question 36

What are some important characteristics of Vibrio cholerae?

Answer 36

Most common species to infect humans

Can survive in freshwater

Causes cholera (particularly O1 EI Tor strain)

Humans infected by ingesting contaminated food and water

Most imporant virulence factor- cholera toxin

Question 37

What are the six steps to how the cholera toxin works?

Answer 37

1. Cholera toxin binds to membrane of epithelial cell by B subunit
2. Portion of the toxin (A) enters cell and is cleaved into A1
3. A1 activates adenylate cyclase
4. Cyclic AMP is synthesized
5. Cyclic AMP stimulates the cell to secrete ions and electrolytes
6. Water follows into the lumen

Question 38

What are the symptoms of cholera? How is it diagnosed, treated, and prevented?

Answer 38

Characterized by severe dehydartion, metabolic acidosis, hypokalemia, and hypovolemic shock

May lead to muscle cramping, kidney failue, coma, and death

Diagnosis- based on characteristic diarrhae, explosive, watery, colorless, odorless, typically flecked with mucous (rice-water stool)

Treatment- fluid and electrolyte replacement, antimicrobials not very effective, doxycycline

Prevention- adequate water and sewage treatment

Question 39

What are the diseases caused by V. parahaemolyticus?

Answer 39

Able to survive in salt water

Results from ingestion of shellfish

Causes cholera-like gastroenteritis

Question 40

What are the diseases caused by V. vulnificus?

Answer 40

Septicemia due to consumption of contamined shellfish

Infections can result from washing wounds with contamined seawater

Question 41

What are some important characteristics of Campylobacter jejuni?

Answer 41

Likely most common cause of gastroenteritis in U.S.

Gram negative, slightly curved, poxidase positive, motile

Microaerophilic and capneic (differs from Vibrio)

Disease is zoonotic and many animals serve as a reservoir

Humans infected by consuming contaminated food, water, milk- Poultry most common source of infection

Bacteria posseses adhesins, cytotoxins, and endotoxins

Infections produce self-limiting bloody and frequent diarrhea

Proper food handling and preparation may prevent spread

Question 42

What are some important characteristics of Helicobacter pylori?

Answer 42

Slightly helical, motile bacterium, colonizes the stomach of hosts

Urease positive- characteristic for colonizing the stomach, raises pH of stomach and neutralizes it by producing ammonia

Causes gastritis and most peptic ulcers

Long term infection is a significant risk for stomach cancer

Question 43

What are the virulence factors of Helicobacter pylori?

Answer 43

Protein that inhibits acid production

Flagella that help the pathogen to burrow through the mucosa

Adhesins, enzymes, and urease

Question 44

How is a Helicobacter pylori infection diagnosed, treated, and prevented?

Answer 44

Diagnosis- positive urease test, biochemical tests

Treatment- antimicrobials in combination with drugs that inhibit acid production

Prevention- good hygiene, proper food handling, and adequate sewage treatment