Part 59

Speaking for the Philadelphia Garden, I have come to the conclusion that on the whole parasitism does play an important part of our annual losses. The financial loss which could be charged against spiroptera alone is in the four figures, to say nothing of the difficulty of replacement of rare species. And while touching the financial phase let it be added that scientific work done now, it must be remembered, is not restricted to the present time or place, but is to be measured in dollars and cents with the yard stick applied to the future, and in other places than that where the initial work is done. Even if we cannot answer the question of the matter of importance the world over we can guarantee that it is sufficiently so in the Philadelphia and London Gardens to warrant a rigid supervision for parasitism; and since the other larger collections are probably made up of similar animals, albeit in different proportions, we surmise at least that it is likewise so with them.

IMPORTANCE OF PARASITES IN OTHER FIELDS.—In addition to their importance to exhibitions, animal parasites of wild animals are important first to man. The animal hosts may serve as porters of infestation, and interfere with attempts at eradication of the disease. The experience of the European with African sleeping sickness attests to this. Not to go farther than immediate examples I wish to note in this connection the occurrence in this Garden of scabies in an orang which was transmitted to a keeper, and of amebic dysentery in monkeys. Leiper[117] has called attention to a guinea-worm in a leopard.

Parasites are important to certain wild animal industries. The ones that have come to my attention are the fur seal (_Otoes alaskanus_) industry of the Pribiloff Islands and fox-farming in Newfoundland. In both of these instances the hookworm was concerned and entailed losses of thousands of dollars. Lucas, who conducted a United States Government commission to the seal grounds and after whom Stiles named the parasite, has left very full notes of the former disease. I have identified the same infestment in a young California hair seal (_Zalophus californianus_) which was born and died in this Garden. This indicates that the parasite might perhaps be found farther down the Pacific coast than hitherto suspected.

To hunters parasitism of animals must be important, but to an unknown and undoubtedly unimagined extent. The grouse plague of Scotland[118] is an example to point. Who knows but that the disappearance of some of our game animals, particularly birds, was not due more to disease than to the ravages of man? There is at least food for thought here.

OCCURRENCE OF ANIMAL PARASITES IN THE WILD.—It would be unbelievable that parasitism did not exist in the wild. It seems proper, however, to record some evidence. Diesing’s _Systema Helminthum_ is replete with references to Natterer’s Brazilian expedition. Nicoll speaks of a German expedition to Spitzbergen in 1898, and a Swedish one to Egypt in 1901, in both of which large numbers of parasitic forms were collected. Nicoll[119] found _Trichosoma hepaticum_ in a hare shot in the wild, and liver-flukes[120] in a kestrel shot on the coast of Scotland. Leiper[121] found nine species of worms in hippopotami during an expedition to Uganda, and[122] states that thirty-seven species of helminths were collected on an Antarctic voyage by Surgeon Atkinson. In an investigation of Grouse disease in Scotland, Fantham found many different blood and intestinal parasites. Dr. Charles B. Penrose tells me that all of the white-tailed deer he shot in the valley of the Swan River, Montana, were infested with liver-flukes, so much so that the liver was literally riddled by the disease, and yet the deer were fat. The black-tail deer of the same valley were not thus parasitized and were not as fat. In our own Garden we have found many tapeworms in wild cats[123] which had been too recently captured for the worms to have developed in captivity. Such instances might be still further multiplied.

A more important consideration is the fate of the parasites thence introduced into our Garden. Do they disappear of themselves? Naturally we can never make sweeping predictions, for future events will depend upon the life history of the individual parasite concerned. But by and large, once introduced it is better to assume the attitude of pessimism, and resign oneself against spontaneous disappearance and, what is worse, realize that the parasitism is likely to become indigenous. We have several pieces of evidence, however, that the infestment may occasionally quite disappear. Thus, I have seen _Coccidium bigeminum_ spontaneously disappear from a Swift Fox (_Canis velox_) and _Spiroptera incerta_ from a Macaw as proven at autopsy. Nicoll[124] remarks that certain trematode infestations were heavier in newly arrived animals than in ones long resident in the Garden. This is conceivable on the basis of individual worms dying out, _i.e._, fulfilling their life spans without the host becoming reinfested with fresh parasites. Precise information on the subject is supplied by Ackert[125] who found that cestodes disappeared from chickens in six to eight months when the birds were confined, _i.e._, protected from reinfestment. Moreover, it is known that worms can escape during acute infections, the infectious state of the economy producing conditions obnoxious to the parasite. We hear of many instances of their expulsion in human feces and vomitus during malaria and the exanthemata of childhood and know of similar discharge from animals during the death agony. I cite these data largely because they explain the scarcity or absence of parasites at autopsy in animals which were known to have been clinically infested.

FREQUENCY OF PARASITISM IN WILD ANIMALS

There can be little doubt that wild animals are more frequently infested than man, and furthermore with a larger number of parasites. I have no statistical basis for these opinions—they rest on personal observations of human and animal autopsies, and reports of findings in the tropics and elsewhere. They have therefore but the value of an individual opinion. I should estimate rather cautiously that wild animals are infested at least two or three times as frequently as man and much more heavily.

The first step in the discussion of the incidence of parasites must be that respecting the (host) classes and smaller taxonomic divisions—of course as they have been studied in this Garden. Certain statistical limitations were experienced and can be summarized as follows:

Data are not available on a sufficiently large number of animals to justify conclusions as far down as genera and species, except for such commonly and generously exhibited forms as monkeys and parrots. I have therefore in tabulating and reviewing our records, distributed the animals only as far as families—not into genera and species. The table (24) to follow will be found not to contain every family because to do so would needlessly enlarge it. Accordingly I have followed the policy of only indicating those genera and species showing either frequent or important infestment. I shall refer to those groups later as “susceptible” groups. If no family is recorded in the table it means that we have had no important numbers of infestments in it. The “remarks” column shows the individual parasite that has been particularly frequent or otherwise important. If there are no remarks it means that the species of parasites found have been scattering.

RESULTS OF REVIEW AND TABULATIONS.

We now pass to an analysis and discussion of the findings brought out in the previously mentioned review of our records and in Table 24. Viewed broadly we find that there is a wide variation in the susceptibility of different families to infestment. Those that are susceptible may be located by consulting the table, and each will therefore not be separately culled out and subjected to needless repetition. A few points are however worthy of separate mention. While there is a familial or generic susceptibility within certain orders it is unwise to generalize too broadly. Thus for example the Corvidæ have a high percentage in incidence for tropidocerca, syngamus and periproventricular worms, many families of Ungulata harbor echinococcus, and Carnivora are prone to show ascarids. On the other hand, among the copious exceptions to this may be cited the irregular liability to infestment exhibited by the Galli. Four varieties of these birds are represented but there are missing such important kinds as curassows, guans, guinea fowl and peafowl.