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Rickettsial infections
Rickettsiae are similar to bacteria but are
smaller . They are an obligate
intracellular m.o.and can infect human
and animals .
The m.o. enter the endothelial cells of
small blood vessels and capillaries
causing thrombosis , bleeding and
necrosis of involved tissue.
Example of rickettsial disease : epidemic
typhus, spotted fever & trench fever .
Spotted fever with thrombosed vessel &
vasculitis
Chlamydial Infections
 Group of spherical microorganisms intermediate
in size between large viruses & bacteria
 They are obligatory intracellular microorganisms
, proliferate only within host cells, although some
may survive extracellularly. They are unable to
synthesize ATP at all.
 Infection spread by a small compact spore-like
form (elementary body) which can survive, but not
divide extracellularly.
Chlamydial Infections
1-In man they are responsible for the sexual transmitted
disease lymphogranuloma venerium, which is a small
ulcerating primary lesion in the genitalia but with
satellite abscess in the inguinal lymph node with
extensive scarring & strictures in the anogenital tract .
In active lesions, the diagnosis of lymphogranuloma
veneruim is by demostrationof the organism in biopsy
sections or smears of exudate.
In more chronic cases the diagnosis rest with
demonstration of a.b. to the chlamydial serotypes in
patients serum.
2- They cause eye infections, most important is trachoma,
which is one of the 10 commonest causes of blindness.
3- Inhalation of microorganism from parrots cause
pulmonary infection called psittacosis, results in
granuloma formation.
This is a conjunctival scraping from the eye, with
Giemsa stain, reveals an intracytoplasmic
elementary body of Chlamydia trachomatis in the
cell.
4-Inhalation of microorganism (other than that from parrots)
results in mild interstitial pneumonia called chlamydial
pneumoniea.
5-It causes Chlamydial urethritis & pelvic inflammatory
disease.
Unlike N. gonorrhoae urethritis ,C. urethritis in men may
be asymptomatic, so infected men might not seek
treatment.
Mycoplasmal infection
 They are very small filamentous or coccobacillary
microorganisms which lack cell wall, but classified
as a bacteria.
 They are distributed widely & are pathogenic to many
animals & plants.
 In man only one species, Mycoplasma pneumoniae,
has been shown conclusively to be pathogenic.
MycoplasmaL pneumonia
 It is the cause of one form of non –bacterial
(atypical or interstitial) pneumonia which is
endemic in most parts of the world esp. in children.
 May result in meningo-encephalitis if
disseminated in the body with low immunity.
 The immune response includes the production of
a.b. which cross reacts at low temp. with a human
RBC a.g. &in some cases is responsible for acute
Haemolysis.
Fungi
• Thy are classified into 3 groups:
1- Yeasts: round or oval unicellular organism that
replicates by budding or binary fission, some yeasts
can form chains so called pseudohyphae.
2- Moulds: Multicellular organisms that grow in form
of branching tubules called hyphae, which may be
septate or non-septate.
3- Dimorphic fungi: can grow as yeasts or moulds.
Budding cells with pseudohyphae seen here are
characteristic for Candida infection.
With a PAS stain, the budding cells and pseudohyphae (short
filaments that are not true hyphae) of Candida stain bright
red.
Candida albicans:• Most common fungal infection.
• It form yeasts & pseudohyphae.
• Normal commensal of moist skin, mouth & intestine.
• Disease occurs usually after the use of antibiotic because
commensal bacteria inhibits candidal proliferation.
• System dissemination results in multiple abscesses
occur in immunosuppressed patient.
Body diseases caused by Candida
• It may involve vagina particularly during
pregnancy, mouth particularly in infants, oral
thrush & in-patients with oral antibiotic therapy.
• In patients with T-cell deficiency it causes mucocutaneous candidiasis (chronic disfiguring
condition) affecting principally face, scalp &
mouth.
• Systemic candidiasis is rare seen in
immunosuppressed or debilitated patients as
multiple small abscesses esp. in kidneys.
Oral candidiasis is common in immunocompromised hosts,
such as those with HIV infection. There is a hairy coating of
the tongue seen here mixed with a pale tan exudate.
Protozoa
Toxoplasmosis:
• Caused by Toxoplasma gondii.
• It can be either acquired or congenital.
1-Acquired toxoplasmosis:
• Results from food contaminated by faeces of pets
especially cats, or eating of undercooked meat
contaminated by the parasite.
• Most are asymptomatic.
• In symptomatic cases, there is lymphadenitis,
esp. of cervical L.N & fever.
• In immune suppressed patient it can cause
encephilitis and hepatitis.
1-Acquired toxoplasmosis:
Pathology:
•
The lymph node affected shows:
1- Lymphoid follicle hyperplasia.
2- Microgranuloma.
3- Monocytoid B-cell hyperplasia.
Toxoplasma gondii infection can result in the formation of
pseudocysts, which have the infected cell forming the cyst
wall, and the cysts contain bradyzoites. Pseudocysts are
seen here in cerebrum in a microglial nodule
Toxoplasma gondii infection can also occur in the heart.
Here a pseudocyst appears in myocardium.
Congenital toxoplasmosis
• Following transplacentral spread from
infected but often asymptomic mother.
• It can cause abortion, stillbirth, cerebral
necrosis , hydrocephalus or blindness.
SARCOIDOSIS
• Chronic granulomatous disease of
unknown etiolgy
• Rare in our locality
• Has chronic coarse with relaps & remision
• Affect skin , lymph node,bone , lung etc
• Microscopic appearance noncaseating
epitheloid granuloma .The giant cell
contain calcified bodies ( Schaumanns
bodies)
Diagnosis
• Clinical
• Skin test: Kviem test .Intradermal injection
of sarcoid tissue .In 4 wks nodule develop
has sarcoid appearance
• Biopsy
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