Parasitic diseases in animals

Gastrointestinal parasites of animals

Nature

Parasitic animal diseases cause severe economic losses, and some may also be transmitted to human beings. They inflict traumatic, lytic, obstructive, intoxicative, allergenic and proliferative damage on the host, or cause loss of nutriment. In addition, the damage done by parasites may enable bacteria and other pathogens to enter the tissues and set up diseases. There are two main varieties of parasites: protozoa and metazoa. The main classes of protozoa are rhizopods, ciliates, flagellates and sporozoans. Metazoa comprise helminths (parasitic worms) of five separate groups: nematoda (roundworms), nematomorpha (gordian worms), platyhelminthes (flukes and tapeworms), acanthocephala (spiny-headed worms) and annelida (leeches); and arthropods, which can be pathogenic 'per se' or may transmit diseases (by virus, bacteria, protozoa and helminths). Main parasitic animal diseases include trypanosomiasis, liver fluke, blood fluke, trichinosis, toxoplasmosis, babesiosis, theileriosis, besnoitiosis, myiasis, leishmaniasis, mange, filariasis. Bacteria, viruses and fungi may also be parasitic.

Background

Parasitic diseases in animals emerged as a global concern in the late 19th and early 20th centuries, when advances in veterinary science revealed their profound impact on livestock productivity and public health. Outbreaks such as rinderpest and trypanosomiasis highlighted the transboundary nature of these diseases, prompting international surveillance and research. Over time, the recognition of zoonotic risks and economic losses deepened appreciation of their significance, leading to coordinated control efforts worldwide.

Incidence

Parasitic diseases in animals are a persistent global concern, affecting livestock, wildlife, and companion animals across continents. These diseases contribute to significant economic losses in agriculture, threaten food security, and can facilitate the transmission of zoonotic infections to humans. The World Organisation for Animal Health (WOAH) reports that parasitic infections such as trypanosomiasis, fascioliasis, and tick-borne diseases are endemic in many regions, with millions of animals impacted annually, particularly in Africa, Asia, and Latin America.
In 2022, an outbreak of East Coast fever, caused by the protozoan parasite *Theileria parva*, devastated cattle populations in Kenya’s Rift Valley. The epidemic led to the loss of thousands of animals, severely affecting local pastoralist communities and prompting emergency vaccination campaigns.