ABSTRACT
Primitive members of the animal kingdom, parasites may be classified as either Protozoa or Helminths. Protozoa are primitive unicellular animals. Blood protozoa primarily produce intravascular infections, such as malaria, babesiosis, and trypanosomiasis; tissue protozoa are largely intracellular parasites and include the agents of toxoplasmosis and leishmaniasis; gut protozoa are usually confined to the gastrointestinal tract and include the agents of amebiasis and giardiasis. The trypanosomes are arthopod-borne parasites characterized morphologically by flagella. The parasites exist extracellularly in blood, lymph, or cerebral spinal fluid. Leishmania are intracellular parasites transmitted from man to man by sandflies. They produce cutaneous, mucocutaneous, or visceral infections. A characteristic of Helminthic infections is that the parasites, once in the body, do not multiply. Each egg or larva can become only one adult. Trematodes live either in the tissue of the host or in the gastrointestinal tract; larvae may also have a distinct tissue phase. The only studies dealing with complement and trematodes relate to schistosomiasis.
