• Rickettsiae and Chlamydiae- obligate
intracellular organisms.(classif. as bacteria)
• Rickettsia General features:
-parasites of gut cells of athropods.
-transmittion- athropod to animal.
Genera of the Family Rickettsiaceae:
-11 spp (do not multiply within vacuoles & do
not parasitize wbcs.
- 2 spp obligate intracellular parasites
– do not multiply within vacuoles but do
• 3. Coxiella:
– (1 spp) obligate parasite
–grows preferentially in vacuoles of host cells.
• 4. Baartonella
– 3 spp
- intracellular parasite which attacks the rbc.
Fundamental differences btn Chlamydiae and
Cytochromes +ve No cytochromes
Aerobic metabolism Anaerobic metabolism.
Multiply by binary fision. Single development cycle.
Small, pleomorphic coccobacillary forms
Obligate intracellular parasites.
All contain DNA and RNA.
Susceptible to various antibiotics.
Cell walls resemble those of Gram –ve bacteria.
Require exogenous cofactors from animal cells.
Most grow readily in the yolk sac of embryonated eggs
and in cell cultures.
Structure of Rickettsia.
• Typical rickettsia
– Very similar to that of gram-negative bacteria.
• Typical envelope:
– Innermost cytoplasmic membrane, a thin electron
dense rigid cell wall & outer layer
• Cell wall
– Chemically similar to Gram-ve bacteria i.e contains
diamino pimelic acid and no techoic acid.
• No discrete nuclear structure.
In dil.buffered salt soln:
– Unstable, losing both metabolic activity and infectivity for
In enriched medium:
– Can survive for may hrs.
Basis for obligate parasitism:
– Require rich cytoplasm to stabilize unusually permeable
Require exogenous supply of cofactors.
Growth and Multiplication.
Transverse binary fission.
Under poor nutrition:
long filamentous forms.
Immediately after division:
– Extensive movements through the cytoplasm of the cell.
– Enclosed in a persistent vacuole during growth and
6-10 daughter cells form within the host cell before
ruptures and releases them.
• Both Cellular and Humoral immunity may
• Endemic (murine) typhus:
– primarily maintained in rodent populations.
– transmitted via the flea.
– Humans ( accidental host).
• Spotted fever:
– Found predominantly in animals.
– Transmitted by the tick.
– Humans (accidental hosts).
• Q fever:
– Mostly in animals.
– Humans acquire disease primarily by inhalation of
• Epidemic typhus and trench fever:
– transmitted from human to human via the louse.
– Transmittion: via arthropod vectors;
• Q fever :
– via inhalation or ingestion of contaminated milk or food.
• The bacteria enter host endothelial cells via an induced
– Phospholipase A may help in penetration.
• Replication of the bacteria causes lysis of the host cell
and consequent spread to other cells.
• Initial replication:
– At the site of entry producing a local lesion.
– Followed by dissemination via the vascular system producing
vasculitis and a skin rash.
– The lesions may become necrotic
• Virulence :
– Probably due to many factors including:
• release of endotoxin,
• production of immune complexes
• hypersensitivity reactions.
• A characteristic triad of symptoms include:
– headache and
– rash (no rash with Q fever).
• These diseases present as:
– febrile illnesses after exposure to arthropods or animal hosts
or aerosols ( endemic areas).
– High mortality from Spotted fever (delayed diagnosis).
• The spread of the rash ( characteristic):
– spread from the trunk to the extremities (centrifugal)- typical
– spread from the extremities to the trunk (centripetal)
-typical for spotted fever.
1. Macchiavello stain:
- organisms bright red V blue background.
1. Castaneda stain:
- blue organisms V red background.
1. Giemsa stain:
- bluish purple organisms.
4. Use of immunofluorescent antibodies:
NB: The organism can be inoculated into tissue culture
and grown over 4-7 days (very hazardous to personnel).
• Serological reaction:(Weil-Felix test):
– The production of serum antibody reactive against
Proteus OX19, OX2 or OXK antigens is determined
• Embryonated eggs.
– (Q- Fever)
• Cell cultures.
Important Rickettsial diseases of animals
Tropical canine Pancytopenia.
Equine and Canine Ehrlichiosis.
Potomac horse Fever.
Treatment & Control
– Tetracycline or
– Arthropod and rodent control are possible but
– No vaccines - currently available.
Chlamydia General characteristics
• Species: trachomatis, psittaci
• The Chlamydia
– Obligate intracellular parasites.
• C. trachomatis
– Inclusion conjunctivitis,
– Lymphogranuloma venereum (LGV)
– nongonococcal urethritis (NGU). I.e, oculourogenital
• C. psittaci produces systemic diseases:
– ornithosis and
• Have two distinct forms:-
– Infectious elementary bodies and
– Intracellular reticulate bodies.
• Elementary bodies attach and are internalized by
susceptible host cells.
• Once inside, they reorganize into a replicative form (the
• Over a 24 hour period:
– Reticulate bodies divide and begin to reorganize back into
• 48-72 hours after infection:
– The cell is lysed and
– numerous infectious elementary bodies released.
• The genome of Chlamydia is only 25% the size
of E. coli (i.e one of the smallest prokaryotes).
• The pathogenic mechanisms employed by
Chlamydia - not well understood.
• No detectable flavoproteins or cytochrome.
• Basis of obligate intracelluar parasitism
– lack of ATP-generating ability
– Obtain ATP from the host cell.
• The cells can synthesize :
– RNA and
• C. psittaci is acquired from infected birds,
usually via the respiratory route.
• C. trachomatis is spread via the fingers to the
urogenital area and vis versa.
– Infection of the epithelial cells of the conjunctiva,
producing inclusion bodies.
– Vascularization and clouding of cornea along with
trichiasis (inward growth of eyelashes) ---- produce
scarring leading to blindness.
• Inclusion conjunctivitis
– Milder form,
– Occurs in both children and adults.
• Sexually transmitted nongonococcal urethritis
– Similar to gonorrhea
– Occurs with greater frequency.
• Lymphogranuloma venereum (LGV) involving
inguinal lymphadenopathy ("buboes") can occur
• Chlamydia induce interferon and are sensitive to
• During infection, antibodies are synthesized but
recovery is not generally protective.
– prevalent in Africa and Asia,
– generally in hot and dry areas.
• The organisms are very persistent.
– Their habitat : similar to that of Neisseria and
• Infection can occur via:
– swimming in unchlorinated pools,
– sharing towels or
– by passage through the birth canal.
– Diagnosis of trachoma is usually good.
– Genital vesicles associated with LGV are characteristic.
– NGU can only be suspected in the absence of laboratory
– Iodine stained specimens usually show inclusion bodies.
• Tissue culture:
– Chlamydia can be cultured in tissue culture and appropriate
serological tests performed
• Micro-immunofluorescent tests in tears of patients
with eye infections for presence of anti-chlamydia
• Delayed –type skin rexn (hypersensitivity Type
• Rising titer of Ab V chlamydial family Ag in lung
Treatment and Control.
• Chlamydia exhibit low pathogenicity in a compromised
– Tetracycline or erythromycin are drugs of choice.
– Good hygiene,
– Treatment of sexual partners and
– Quarantine of birds all reduce the incidence.
Treatment and control.
– No vaccine – available since specific antibodies fail
to neutralize elementary bodies in vivo.
• Chlamydial d’ses –relatively easy to treat, but:
1.Latency of infection
2.Susceptibility to reinfection.
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