Chapter 21: Rickettsias, Chlamydias, Spirochetes, and Vibrios Flashcards
(44 cards)
What are some general characteristics of family Rickettsias?
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
What are some general characteristics of the Rickettsia genera?
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
What are some important general characteristics of the 3 species of Rickettsias?
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
What is the disease caused by Rickettsia rickettsii?
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
How do you diagnose and treat Rocky Mountain Spotted Fever?
Diagnosis by Fab test and prevention involving avoiding ticks
Treatment- removal of ticks and doxycycline
What is the disease caused by Rickettsia prowazekii?
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
What is the reoccuring disease caused by the Rickettsia prowazekii?
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
What is the disease caused by Rickettsia typhi?
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
What is the disease caused by Orientia?
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
What are the characteristics and diseases caused by Ehrlichia and Anaplasma?
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
What is the growth and reproductive cycle Ehrlickia and Anaplasma?
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
What are some general characteristics of Chlamydias?
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
What is the developmental cycle of a chlamydia?
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
What are the virulence factors of Chlamydia trachomatis?
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
What are the diseases caused by Chlamydia trachomatis?
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
How are chlamydia trachomatis infections diagnosed, treated, and prevented?
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
What are the diseases caused by Chlamydophila pneumoniae?
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
What are the diseases caused by Chlamydophila psittaci?
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
What are some general characteristics of Spirochetes?
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
What are some general characteristics of Treponema:?
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
What are the virulence factors of Treponema and what disease does it cause?
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
What are the four stages of syphilis?
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
How is a syphilis infection diagnosed, treated, and prevented?
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
What are the other types of disease caused by Treponema?
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
