Chapter 6 PHYLUM MICROSPORIDA

 

 

 

6.1 ENCEPHALITOZOON AND NOSEMA

Spore-forming protozoans of the phylum Microsporida. Most species are parasites of lower vertebrates or invertebrates, but a few species infect man or his domestic animals. Our discussion will be restricted to the genera Encephalitozoon and Nosema

6.1.1 Classification

A. Phylum Microsporida

1. Characteristics of Microsporidia

• a. all are parasitic
• b. most produce spores with a polar filament
• c. An amoeboid sporoplasm is the infective stage inside the spore 

Figure 2.49: A Typical Microporidian spore

B. Encephalitozoon sp.

• 1. Parasites of rodents, rabbits, carnivores and primates including man.

C. Nosema spp.

• 1. Parasites of invertebrates and rarely man.

6.1.2 Geographic distribution: worldwide

6.1.3 Epidemiology

• A. Microsporidan infections are initiated in new hosts by ingestion of mature spores
  • 1. Ingestion of spores from the environment
  • 2. Ingestion of viscera of infected animals that contain mature sproes.
  • 3. Evidence exists that transplacental infection may occur

6.1.4 Life Cycle. Terminology and Morphology of the Different Stages 

6.1.5 Pathology and Pathogenicity (Encephalitozoon)

A. Dog and other carnivores

• 1. Principle signs are ataxia, posterior weakness and convulsions
• 2. Anorexia, thirst and reduced growth have been reported
• 3. Blindness is a reported sequela
• 4. Principle lesions are typical of encephalitis, or meningoencephalomyelitis.
  • a. Tiny foci of cortical necrosis
  • b. Scattered accumulations of glial cells
  • c. Mononuclear perivascular cuffing
  • d. Accumulations of organisms are often visible in areas of necrosis
• 5. Kidneys may have white spots on the external surface
  • a. Microscopically, the white spots represent monuclear -cell inflammatory infiltrates
  • b. Accumulations of organisms may be seen in the infalmmatory infiltrate
  • c. The lesions have been described as typical of severe interstitial nephritis and arteritis

B. Rabbits

• 1. Encephalitozoonosis is usually a mild, chronic infection, althogh paralysis and death may occur
• 2. Brain lesions are similar to those described for carnivores
• 3. Chronic nephritis may be the outstanding feature of the disease in rabbits
  • a. Kidney lesions are focal granulomata often containing organisms
  • b. The tubules degenerate and often are surrounded by a diffuse interstitial mononuclear-cell infilatrate

C. Man

• 1. Predominant presenting sign in man is encephalitis 

6.1.6 Pathology and Pathogenicity (Nosema)

• A. Nosematosis (Nosema connori) has been reported in humans
  • 1. Signs included intermittent diarrhea, vomiting, irritability and lethargy
  • 2. Organisms were present at necropsy in many organs including kidney, liver, urinary baldder,m adrenals and diaphragm. Organisms were also recovered from the muscularis of the intestine.

6.1.7 Diagnosis of Encephalitozoanosis or Nosematosis

A. Histologic examination of infected organs

• 1. Spores are:
  • a. Gram positive
  • b. Variably acid-fast
  • c. PAS-positive at 1 end
  • d. Argyrophilic

B. Serology

• 1. Indirect fluorescent antibody test (IFAT)
• 2. Skin test (Delayed hypersensitivity reaction -DHR)
• 3. Rabbits
• 1. Encephalitozoonosis is usually a mild, chronic infection, although paralysis and death may occur
• 2. Brain lesions are similar to those described for carnivores
• 3. Chronic nephritis may be the outstanding feature of the disease in rabbits
  • a. Kidney lesions are focal granulomata often containing organisms
  • b. The tubules degenerate and often are surrounded by a diffuse interstitial mononuclear-cell infiltrate

C. Man

• 1. Predominant presenting sign in man is encephalitis