Rickettsial infectionsRickettsiae 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 Infections1-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 muco-cutaneous 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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