Final answer:
Small strongyles, a group of parasitic nematodes, make up the majority of the worm load in horses. They, along with other nematodes like Strongyloides stercoralis and Enterobius vermicularis, impact human and animal health significantly.
Step-by-step explanation:
The majority of the equine worm load is attributed to small strongyles, also known as cyathostomins, which are a type of nematode parasite. These parasitic nematodes are a major concern for horse health as they can inhabit the intestines and cause various degrees of pathological effects. In contrast, Strongyloides stercoralis, another nematode, causes strongyloidiasis in humans by penetrating the skin, usually through the feet, migrating to the lungs, and finally to the intestine. Enterobius vermicularis, known as the pinworm, is transmitted via the fecal-oral route and can lead to enterobiasis, primarily in human hosts. Both of these are examples of the significant impact nematodes can have on health.
Helminths, including nematodes like roundworms, pinworms, hookworms, and whipworms, are widespread intestinal parasites. Other groups of helminths include cestodes (tapeworms) and trematodes (flukes). These parasites can significantly affect global public health and are more common in areas with poor sanitation. Ascariasis, for example, is caused by Ascaris lumbricoides, an intestinal roundworm that infects nearly a billion people worldwide.