ANIMAL PARASITES AND HUMAN DISEASES

PARASITES fall only roughly into the two categories implied in the title of this discussion. While a few of them are totally dependent upon human hosts, and some are able to develop only in other animals, a majority of the parasites commonly referred to as "parasites of man" are in reality parasites of other animals. In the latter group are such familiar examples as Trichinella, found in rats and many other animals, including pigs; Balantidium and some lesser protozoa of pigs; Toxoplasma, which occurs in many wild and domesticated animals. Trypanosoma cruzi, which is carried by a variety of animals, is the cause of Chagas' disease commonly seen in parts of South America and found recently in a child in Texas. Other examples include Isospora of undetermined hosts, possibly including the dog; Trichostrongylus species that commonly are found in sheep and goats; the small tapeworms, Hymenolepis nana and Hymenolepis diminuta, of rats and mice; and the common dog tapeworm, Dipylidium caninum. There are others whose endemicity in any area depends somewhat on the presence of suitable non-human hosts, and still others that are able to reach maturity in man but are rarely involved in medical problems because infection is acquired only by eating uncooked earthworms and insects. It might be mentioned, as a matter of interest, that occasionally other animals may acquire parasitic diseases from their human associates, as for example dysentery and diarrhea in dogs, caused by Entamoeba histolytica and Strongyloides stercoralis. In all of the above mentioned parasitic infections, diagnosis is usually based on conventional laboratory methods, and both clinical and laboratory workers are generally familiar with the problems presented by them.