Toxoplasmosis and Chagas Disease: Parasite Forms and Epidemiology

Toxoplasmosis: The Zoonotic Infection

Zoonosis caused by the intracellular protozoan Toxoplasma gondii (Apicomplexa). It is one of the most widespread infections in nature. Forms of presentation of T. gondii include:

Tachyzoite

Shaped like a bow and is 4 to 6 mm in length. This is the form in which the parasite multiplies actively during the acute phase of infection.

Cyst

These are round or elongated and are 20 to 200 m.m. Inside are the bradyzoites. They are located in tissues, primarily the CNS, muscle, and eye. They are present in the chronic stages of infection, appearing induced by the host immune response.

Oocyst

It is rounded, is 10 mmy and has two sporoblasts. In the external environment, it is eliminated through the stool of the cat. Environmental conditions are required for its maturation.

Chagas Disease (American Trypanosomiasis)

Disease caused by flagellate protozoa of the Family Trypanosomatidae that require a biological vector to complete their cycle. African trypanosomiasis, or sleeping sickness, is a different disease with a different geographical location.

Vector Biology: Triatoma infestans

Insects of the Reduviidae, Triatominae subfamily. The cycle includes domestic and wild cycles involving species like T. spinolai and T. proctata. They are hematophagous and nocturnal. Habitat: cracks in adobe walls. Found in Chile: Region I to VI.

Trypomastigotes

Fusiform, 20 mm long, with a central nucleus and a kinetoplast posterior to it. Found in mammalian blood and the triatomine hindgut. This is the infective form in both hosts and the form of blood spread in mammals.

Epimastigotes

Similar to the above, but the kinetoplast is anterior to the nucleus. This is the form of multiplication in the intestine of Triatoma and is predominant in culture media.

Amastigote

Rounded, 2 mm in diameter, with a short flagellum (scourge). This is the intracellular multiplication form in mammals.

Epidemiology

Presence throughout the Americas. Chile: Regions I to VI, rural and peri-urban areas.

Transmission Mechanisms

Transmission mechanisms include:

• Vector-borne
• Transfusion or transplantation
• Congenital
• Accidental exposure

Prevalence Data (Serology)

Prevalence data includes:

• Human Serology: 18%
• Xenodiagnosis: 10%
• Bovine: 13.4%
• Canine: 19.8%
• Equine: 16.8%
• South American Camelids (Cam. Sud): 2 to 10%

Control and Assessment

WHO (1991): Latin American Control Plan. Goals: Eradicate the domestic vinchuca (vector) and interrupt transmission by transfusion. Assessment in Chile (1996): Prevalence among children <10 years old: 1.4% (1996), compared to 5.4% (1982-1990). Overall prevalence in different regions has decreased.