Parasitic infections in humans and animals

Abstract

Parasites are organisms that depend on a host for feeding and reproduction and belong to various unrelated taxa, primarily protozoa, helminths and arthropods. Complex life cycles have often lead to extreme adaptations; nevertheless parasites may harm their hosts and even cause serious disease and death. Transmission of parasite stages can be environmental, nutritional or vectorborne. Among the most important human protozoan parasites in a global context are Leishmania, Plasmodium (both transmitted by bloodsucking arthropods) and Toxoplasma which is soil- or food-borne. Parasitic worms (helminths) relevant for human health include Echinococcus, Toxocara, hookworms (all soil-borne) and Dirofilaria (transmitted by mosquitoes). Various arthropods (ticks, insects) are involved in the transmission of pathogens due to their blood-feeding behaviour. They are especially involved in transmission cycles between animals and humans (zoonotic infections). Research on parasites and their interactions with the host requires suitable animal models. For parasites with a wide host range or those naturally infecting rodent species available as laboratory animals, established models are available. Others, like the human malaria parasites, require sophisticated and often costly genetic manipulation to allow for infection in nonnatural rodent hosts. Alternatively, surrogate models of closely related helminth species in rodent models are used to study human parasites.