VPA 211: General Veterinary Parasitology and Helminthology (3+1)

TYPES OF HOST

• Definitive hosts are hosts that harbour the adult (sexual) form of the parasite. e.g. Sheep for Fasciola gigantica, Dog for Echinoccocus granulosus, and Horse for Habronema muscae.
• Intermediate hosts are those that harbour the asexual form of the parasite (only when there is an obligatory passage through the host).
  • Intermediate hosts may be divided into passive intermediate hosts (snails for trematodes) and active intermediate hosts (Tabanus sp. for Trypanosoma evansi)) 

Passive intermediate hosts (Snails)

Active intermediate host (eg. Tabanus)

• Reservoir hosts are hosts that harbour a parasite of another host without itself getting affected, but act a source of infection for the original host e.g. Game animals for the protozoan parasite Trypanosoma gambiense.
• Carrier hosts are hosts that have a residual population of the parasite and acts as a source of infection for the same type of host.
• Transport hosts are those that harbour the immature/infective stage of a parasite of another host and help in disseminating the parasite without any development in itself. E.g. Earthworms for Egg/larvae of Ascaridia galli

• Paratenic hosts are those that harbour the immature/infective stage of a parasite in an encapsulated form and helps in dissemination of the parasite to the definitive host e.g. Calotes for Spirocerca lupi.

 

• Intercalary host is a host that liberates the infective stages of a parasite of another trapped in the body of the original host E.g. Cats by eating mice liberate the eggs of Capillaria hepatica which are trapped in the liver parenchyma.