- Helminths are multicellular worms that parasitize many organs of the body, most commonly the GI tract

- Transmission by 4 main ways:

o Via intermediate host – accidental ingestion of larvae in tissue of another host

o Faecal-oral route – accidental ingestion of eggs or larvae originiating from faeces of infected host

o Active skin penetration – larval stages invade through skin

o Injection by blood-sucking insect – larval stages develop to infectivity in insect intermediate host

- The most serious helminth infection is schistosomiasis, caused by infection with blood flukes

- The pathology is primarily due to hypersensitivity reactions to eggs as they pass through the tissues

- The outer surface of helminths provide the primary host-parasite interface

- Arthropods of importance in human disease are those that feed on blood or body tissues (insects, ticks, mites) and those which transmit other infections, particularly viruses, bacteria and protozoa