Isospora and Sarcocystosis Overview

Isospora and Sarcocystosis

• Isosporiasis: A diarrhoeal disease, a significant cause of diarrhoea in immunocompromised patients, especially those with AIDS. Previously used as an indicator for AIDS.
• Two species exist: Isospora belli (common) and Isospora natalensis.
• Naturally occurring in animals (e.g., dogs).
• Cosmopolitan distribution, but often underdiagnosed.
• Transmission occurs via ingestion of mature oocysts from human or animal sources.
• Spread through contaminated food or water, faecal-oral route.

Morphology of Oocyst

• Sporulated oocysts are oval/elliptical.
• Contains two sporocysts, each with four sporozoites.
• Surrounded by a thin, smooth, two-layered cyst wall.

Life Cycle (Isospora)

• Infection occurs by ingestion of contaminated food or water containing sporulated oocysts.
• Homoxenous (needs only one host).
• Sexual and asexual life cycle stages occur in the intestinal mucosa.
• Immature oocysts are passed in faeces.

Life Cycle (Isospora)

• Infection via ingestion of sporulated oocysts or food/water.
• Sporozoites released from oocysts penetrate intestinal epithelial cells.
• Sporozoites transform into trophozoites which multiply asexually into merozoites.
• Merozoites invade adjacent cells, continuing the asexual cycle.
• Some trophozoites transition to sexual cycle (gametogony) forming macro and microgametocytes in enterocytes.
• Fertilisation results in a zygote, which develops into an immature oocyst.
• Immature oocysts are excreted in faeces.
• Oocysts mature in the environment.

Clinical Features (Isospora)

• Often asymptomatic.
• Symptoms include abdominal discomfort, mild fever, diarrhoea (watery, without blood or pus) and malabsorption.
• Protracted diarrhoea can be seen in immunocompromised individuals (especially HIV-positive).
• Extra-intestinal infections can involve the biliary tract.

Diagnosis (Isospora)

• Stool examination (wet mount, acid-fast stain) for oval oocysts.
• Molecular methods (PCR).
• Histopathology of small bowel tissue sections.
• Fluorescent staining (auramine rhodamine) and autofluorescence (330-380 nm UV).

Treatment and Prevention (Isospora)

• Usually not required for mild cases.
• Cotrimoxazole for severe cases.
• Prevention: good personal hygiene, adequate sanitation.

Sarcocystosis

• Sarcocystosis: A zoonotic parasite that infects a wide range of animals but transmission to humans is relatively rare. More serious in animals.
• Two types; intestinal and muscular.
• Intestinal Sarcocystosis:
  • Caused by S. hominis (cattle) and S. suihominis (pigs).
  • Humans are the definitive host.
  • Cattle/pigs serve as the intermediate hosts.
• Muscular Sarcocystosis:
  • Caused by S. lindemanni.
  • Humans serve as intermediate hosts.
  • Dogs/cats are the definitive hosts.

Life Cycle (Sarcocystosis)

• Infection via ingestion of sporulated oocysts in undercooked meat (e.g., beef, pork).
• Obligatory two-host (prey-predator) system for life cycle completion.
• Sexual cycle in the intestine of the carnivorous/predator host.
• Asexual cycle in the muscles and other tissues of the herbivorous/prey host.
• Humans (can be both definitive and intermediate host depending on the species of parasite).

Clinical Features (Sarcocystosis)

• Intestinal Infection: Often asymptomatic or mild (abdominal discomfort, nausea, diarrhoea).
• **Muscular Infection: ** Asymptomatic; painful muscular and subcutaneous inflammatory swellings (various parts of body) and eosinophilia.

Diagnosis (Sarcocystosis)

• Intestinal: Stool microscopy (wet mount) for sporocysts.
• Muscular: Histological examination of muscle biopsy (detect sarcocysts).
• Serum antibodies (Western blot).

Treatment and Prevention (Sarcocystosis)

• No specific treatment.
• Symptomatic relief or cotrimoxazole.
• Prevention: Avoid eating raw or undercooked meat and avoiding contamination of food/water with the feces of affected animals.

Morphology (Sarcocystosis)

• Three forms: Oocysts, Sporocysts, Sarcocysts.
  • Oocysts: Found in the intestine of the definitive host . Their sporulation takes place within the lamina propria of the intestinal epithelium. Typical oval and elongated in appearance; a thin-walled structure. It contains 2 elongated sporocysts and each sporocyst contains 4 elongated sporozoites.
  • Sporocysts: Released from the oocysts and excreted in feces of the definitive host. They are considered the infective form for intermediate hosts. They are elliptical in shape; oval with a size ranging from 9-16µm. Contains 4 elongated sporozoites.
  • Sarcocysts; also referred to as muscle cysts and found in the cardiac and skeletal muscles of the intermediate host. Elongated cysts, found longitudinally along the muscle fibre and covered in a thick cyst wall. They are divided into numerous compartments that contain numerous banana-shaped braduyoites/metrocytes.