Rickettsias & Chlamydias Flashcards
Rickettsias (what they encompass)
-bacterial features
-Rickettsia & chlamydia
-Gram neg. bacteria
“between a virus and a bacteria”
How do Rickettsias differ from typical gram neg. bacteria?
- stain poorly w/ gram stain (better w/ Giemsa stain)
- replicate intracellular & w/ rare excpetions, not capable of free-living existence
- Cultured only in viable cells (depend on host cell for energy requirements)
What Rickettsias produce disease in
-how easily destroyed
- produce disease in vertebrates, many are zoonotic
- Most easily destroyed by heat and chemical dsinfectants (Q fever is specific exception)
Pathogenesis of Rickettsiales - 2 familes (Rickettsiaceae & Anaplasmataceae)
-what they have an affinity for
- Family Rickettsiaceae have affinity for lymphoreticular endothelial or leucocytic cells
- vascular damage such as serous effusion and haemorrhages (gives red rash)
- Family Anaplasmataceae: have affinity for RBC and are associated w/ damage to RBC
- result in anaemia and maybe haemoglobinuria
Natural reservoir of rickettsiales
- Arthropod in which they multiply
- usu w/out producing disease
- vertebrates become infected through bites of infected insects (lice or fleas) or arachnids (ticks and mites)
Typhus and typhus like disease
-several species
- e.g. Epidemic typhus (R. prowasekii)
- endemic typus (murine typhus) (R. typhi)
- Rocky mountain spotted fever - v. famous but not in australia (R. rickettsia)
- Qld tick typhus (R. australis) (aka ‘spotted fever’)
- scrub typhus (Orientia tsutsugamushi)
- often disease ass. w/ lots of bush/vegetation
Scrubs typhus (Orientia tsutsugamushi)
- called scrub typhus b.c. gnerally occurs after exposure to areas w/ secondary vegetation
- Transmitted to humans through bite of trombiculid mites (chiggers)
- found throughout mite’s body - highest no. occur in salivary glands
Mite Bites
- what lesion called
- features
- Incubation period of scrub typhus = 10-12 days
- flu-like symptoms initially, and swelling of lymph nodes (lymphadenopathy)
- Lesion (ESCHAR) often seen at site of chigger
- dull red rash may appear all over body
- mortality 6-35%
Qld Tick typhus (R. australis)
- Present in Australia and transmitted by tick in marsupial-tick cycle
- such as Kangaroos
Murine typhus (R. typhi)
-Present in Australia
-Usually a milder disease and not fatal
Mice to fleas to man (aerosolisation inhalation infected flea faeces)
Epidemic typhus (T. prowazekii)
- only infects humans
- transmission cycle = man-louse-man
- humans = reservoir
Rocky mountain spotted Fever (R. rickettsia)
- Present in N. America, NOT australia
- pathogen of man, but mild infection can occur in dogs
- tick transmitted w/ reservoirs in rabbits, rodents, opossums and dogs
Q fever (Coxiella burneti)
- Main reservoirs
- ways it can be transmitted
-Domestic animals (mainly ruminants) = main reservoir
-can be found in wild animals (i.e. ticks in kangaroos)
*zoonotic
Transmitted by;
-milk
-pregnant sheep
-in abbatoirs
-dust in yards
-animal workers
-farmers
Clinical signs of Q-fever in man
- An influenze-like disease w/ low mortality
- Usu. abrupt fever; severe and intractable headache, pneumonitis but no rash
- severe & chronic Q ever may result in complications such as myocarditis, pericarditis or endocaritis
Diagnosis of Q-fever
-Isolation of organims hazardous -> most common diagnosis is by detection of specific antibody in serum (first antibody = IgM; second antibody produced = IgG)
Q-Vax Vaccine
-Protective immunity lasts for many years in response to a single dose of vaccine
Bartonella
- features
- B. quintana (AKA?)
- B. henselae (AKA?)
- features
- Small gram negative
- replicates intracelluarly in endothelial cells and erythrocytes (mammalian reservoir hosts)
B. quintana: “trench fever”
-transmitted by body louse
B. henselae: carried by cats
“cat scratch fever”
-fever + lymphadenopathy (swollen lymph nodes)
-ticks/fleas involved in transmission
Order: Chlamydia
- 2 genera & 6 species of major significance as pathogens in man & domestic/wild animals
- e.g.C. tracomatis, C. pneumoniae, C. psittaci, C. felis, C. abortus, C. pecorum
Developmental cycle of Chlamydia
- Elementary body attaches to surface of cell
- endocytosis of EB occurs
- EB reorganises into reticulate body (which is much bigger)
- RB replicates by binary fission
- RBs reorganised to EB
- Inclusion granule has both RBs and EBs
- in c. pneumoniae and C. trachomatis = reverse endocytosis
- in C. psittaci: lysis of cells and inclusions
Chlamydial diseases
- tend to run chronic courses
- can persist in infected individuals or animals for prolonged periods
- of low pathogenicity except when animals stressed
- trachoma in man due to C. trachomatis (increases in severity as well as in prevalence when personal hygiene and public sanitation are poor)
C. trachomatis
-only infects humans (other species have multiple hosts)
2 syndromes;
1. Trachoma
2. Urogenital infection
C. trachomatis
-Urinogential tract infections
- sexually transmitted
- half of infected women and quarter of men may have no symptoms
- early symptoms include abnormal genital discharge or pain during urination, frequent urination, burning groin
- men may also develop epididymitis (pain or swelling in scrotal area)
C. pneumoniae
-In humans & Koalas
- primarily pathogen in man, but has been isolated from koalas
- is widespread in koalas, but not significant cause of disease
- occ. respiratory disease manifest by coughing, sneezing, serous nasal discharge
- Humans: a common respiratory pathogen in ppl causing mild respiratory signs
C. psittaci
- wild and domesticated birds (most domesticated mammales and wild animals)
- low pathogenicity w/ clinical disease ass w/ stress
- zoonotic
- transmission through direct contact or susceptible animals w/ infected animals or fomites
- inhalation of aerosols containing dried faecal or nasal excretement is also possible
C. abortus
- most common infectious cause of abortion in sheep
- also cause of reproductive failure in cattle, horses and pigs
- zoonotic and can cause severe, life-threatening disease in pregnant women
- infection in pregnant women can result in spontaneous abortion or stillbirths
- typically preceeded by several days of acute influenza like illness (maybe also renal failure, hepatic dysfunction, disseminated intravascular coagulation and possibly death
C. felis
- feline chlamydiosis
- pneumonia and conjuctivitis in cats
- highly debilitating and contagious
- sneezing or nasal discharge may develop
- clinical signs 5-10 days after infection
- transmission = direct cat-cat contact
- vaccines commercially available
- can be zoonotic
C. pecurm in koalas
- ocular disease
- urinogenital tract infection
- urinary incompetence “wet bottom syndrome”
- sexual contact, mother to young and possibly by fighting males (transmission)
- thought koalas acquired infection initially from cattle/sheep
- spreads through urine
Rickettsiales vs. chlamydiales
- Mode of replication
- Dependence on host cell
- Biological vectors
- what they are susceptible to
- cross reaction
MOR - Rick = fission w/ cross-wall formation, daughter cells w/ infectivity of parent cell
-generation time = 18hrs
-Chlamydiales: defined developmental cycle
-generation time = 30 hrs
Dependence - Rick = Limited dependence on host cell
-chlamyd = extreme dependence on host
Bio vectors = Rick = transmitted by arthrodopods (are natural host)
-chlamyd = arthropods not involved in transmission
- both are susceptibility to tetracyclines
- no cross-reaction w/ chlamydia
