Animal parasites and human diseases.

majority of the parasites commonly referred to as “parasites of man” are in reality parasites of other animals.1 In the latter grouip 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 cnuzi, 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.2 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 H mcnolepis diminuta, of rats and mice; and! the common dog tapeworm, Dipylidium caninum. There arc others whose endemicity in any area depends somewhat on the presence of suitable nonhuman 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 occasiona!ly other animals may acquire panasitic diseases from their human associates, as for example dysentery and diarrhea in dogs, caused by Entamoeba histolytica and Strongyloides sterconalis. 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. Iii recent ‘ears attention has been directed to parasitic infections caused by worms which, regardless of length of residence in the human body, do not reach full reproductive maturity and are therefore not diagnosable by the usual laboratory methods. It is of course the larval stages or immature adults that arc involve(! amid!, owing to their tendency to be mostly in the tissues and in many instances difficult to find and identify, the infections caused by them are often unrecognized. Largely for this reason the frequency and severity of infections of this nature have not been fully determined. There are, however, some familiar examples. Certain well known larval tapeworm infections are acquired from other animals. Examples are echinococcus (hydatid) and coenunuis whose infective stages are carried in the feces of dogs, and sparganuim which comes from infected cats and (logs hut nequines development in aquatic hosts before it is infective for man. These infections arc uncommon in the United States and are especially rare in children. It is sometimes stated! that the comiimon ascarids and whipworms of children ( Ascanis lumbnicoides and Tnichuiris tnchiura) are identical with those of pigs. It has not been satisfactorily demonstrated that they are cross-infective to the extent of reaching full maturity in the reciprocal hosts, but it can be safely assumed that when children swallow the infective eggs of pig ascaris, the larvae invade the liver and the lungs even if they fail to reach matumrity in the intestine. Creeping eruption, or cutaneous larva migrans, has been recognized for many years as due to larval stages of the dog and cat hookworm, Ancylostoma brazihiense. It is not always appreciated, however, that other species of ncmatode larvae also producc creeping eruption, and that after a