Sixteen species of wildlife, comprising 1,925 specimens, were examined for Trichinella spiralis during the 1953-1960 period. Species found to be infected with parasites were rat, fox, mink, raccoon, and badger. Initially a high incidence of trichinae was found in the rat, fox, and mink, followed by a marked decline. There is some evidence of a cyclic occurrence in mink. The possible significance of wildlife reservoirs as vectors of trichiniaisis to grain-fed swine is discussed

Biester, H. E.

Hunnard, E. D.

Schwarte, L. H.

Zimmermann, W. J.

University of Northern Iowa

Proceedings of the Iowa Academy of Science Volume 67 Annual Issue Article 71 1960 Epizootiology of Trichiniasis in Wildlife From a Southcentral Iowa Area W. J. Zimmermann Iowa State University E. D. Hunnard Iowa State University L. H. Schwarte Iowa State University H. E. Biester Iowa State University Let us know how access to this document benefits you Copyright ©1960 Iowa Academy of Science, Inc. Follow this and additional works at: https://scholarworks.uni.edu/pias Recommended Citation Zimmermann, W. J.; Hunnard, E. D.; Schwarte, L. H.; and Biester, H. E. (1960) "Epizootiology of Trichiniasis in Wildlife From a Southcentral Iowa Area," Proceedings of the Iowa Academy of Science, 67(1), 578-583. Available at: https://scholarworks.uni.edu/pias/vol67/iss1/71 This Research is brought to you for free and open access by the Iowa Academy of Science at UNI ScholarWorks. It has been accepted for inclusion in Proceedings of the Iowa Academy of Science by an authorized editor of UNI ScholarWorks. For more information, please contact scholarworks@uni.edu. Epizootiology of Trichiniasis in Wildlife From a Southcentral Iowa Area 1 W. J. ZIMMERMANN, E. D. HUBBARD, L. H. ScHWARTE and H. E. BIESTER Abstract. Sixteen species of wildlife, comprising 1,925 speci-mens, were examined for Trichinella spiralis during the 1953-1960 period. Species found to be infected with parasites were rat, fox, mink, raccoon, and badger. Initially a high incidence of trichinae was found in the rat, fox, and mink, followed by a marked de-cline. There is some evidence of a cyclic occurrence in mink. The possible significance of wildlife reservoirs as vectors of trichiniaisis to grain-fed swine is discussed. The persistence of a low incidence of Trichinella spiralis in grain-fed swine indicates that this parasite is disseminated by means other than garbage feeding. In order to determine the possible sources of infection for grain-fed swine, studies were initiated dur-ing the 1953-54 hunting and trapping season to ascertain the possible existence of wildlife reservoirs of Tricldnella in an area of south-central Iowa from which numerous specimens were made available. In 1955 the studies were expanded to include nine additional areas of Iowa. This report is based on the studies from the southcentral Iowa area which continued through the 1959-60 season. Zimmer-mann, Schwarte, and Biester (1956) and Zimmermann, Hubbard, and Biester (1959) reported studies of trichiniasis in Iowa wildlife extending through the 1956-57 season. Eight species of wildlife which were found to be carriers of trichinae are the rat, mink, fox, striped skunk, spotted skunk, opossum, raccoon, and coyote. These were apparently the first reports of T. spiralis in the wild mink, opossum, and spotted skunk. Two or more infected species were found from nine of the 10 sampling areas. Investigations were made to determine possible relationships be-tween infected wildlife and grain-fed swine in the trichiniasis cycle. Two modes of transmission were considered: ( 1 ) direct consump-tion of infected wildlife by grain-fed swine, and ( 2) fecal transmis-sion from infected to susceptible animals. Rats and mice may occasionally be eaten by swine but other species would be less readily available. Zimmermann, Hubbard, and Mathews (1959) found that fecal transmission could occur under experimental con-ditions, a high percentage of transmissions occurring within the first 1Supported in part by a research grant, E606(C5), from the National Insti-tutes of Health, U. S. Public Health Service. Published as paper N.S. 603, Veterinary Medical Research Institute, College of Veterinary Medicine, Iowa State University of Science and Technology, Ames, Iowa. 578 1Zimmermann et al.: Epizootiology of Trichiniasis in Wildlife  From a Southcentral IoPublished by UNI ScholarWorks, 19601960] TRICHINIASIS IN WILDLIFE 579 24 hours after infection of the donor animal. Other controlling fac-tors were size of infective dosages administered to the donor animal and relative immunity of the donor animal. MATERIALS AND METHODS Sixteen species of wildlife, comprising 1, 9 2 5 specimens, were ex-amined for T. sfriralis. In addition to wildlife specimens obtained during the hunting and trapping seasons, rats were obtained from a city dump at various times during the study period. Since most of the wildlife were obtained during the November to February periods, the yearly sampling intervals indicated in this report are from July 1 through June 30. Tissues selected for examination varied with species. The dia-phragm, tongue, and leg muscles were examined from the larger mammals, whereas the entire skinned and eviscerated carcasses of rats and bats were used. Breast muscle was obtained from birds. Tissue samples were ground in individual food choppers; then 45-gm. samples were examined for trichinae by the artificial digestion-Baermann technique. 24 22 20 \ \ \ 18 "' .. ... \ " 16 .. ..i5 ~ 14 ~ \ \ .. 12 "' E'S :z: .. 10 ~ \ ' re \ \ .J" \ / ~ , \ 1954-5 1955-6 1956-7 1957-8 1958-9 1959-60 TIME INTERVAL Figure I. Prevalence of trichiniasis in rats. 2Proceedings of the Iowa Academy of Science, Vol. 67 [1960], No. 1, Art. 71https://scholarworks.uni.edu/pias/vol67/iss1/71580 IOWA ACADEMY OF SCIENCE [Vol. 67 RESULTS Brown rat ( Rattus norvegicus). All rats examined for T. s/Jiralis were obtained from a city dump in southcentral Iowa. The initial group of rats was obtained in May, 1955, followed by a second group in March, 1957. Subsequent groups were examined at two-or three-month intervals until the dump was converted to a landfill type in July, 1959. Seven percent of the 801 rats examined during the study were infected with T. spiralis. The prevalence in the initial group was high, 23 percent of the 61 rats being infected (Figure 1). A de-creased incidence of infection was found in the four following pe-riods of study. The incidence declined to 8.7 percent during 1956-57, followed by 3.4, 6.6, and 2.4 percent in the three remaining intervals. Consecutive samplings of November, 1957, and February, 1958, as well as those of December, 1958, and February, 1959, yielded no infected rats, indicating that trichiniasis was at its lowest level during the winter season. Although not an accurate guide to the intensity of infection, some indication may be obtained by larval counts from 45-gm. (0.1 lb.) tissue samples. In the case of rats only, this included bones. The maximum larval count from rats was 850,000. Another sample con-tained 454,000. Sixteen of the 56 infected rat samples contained more than 10,000 trichinae, whereas 27 contained less than 1,000. 8 6 4\ \ 0 \ \ 12 -\ \ \ 1953-4 1954-5 1955-6 1956-7 1957-8 1958-9 1959-60 TIME INTERVAL Figure 2. Prevalence of trichir.iasis in foxes. 3Zimmermann et al.: Epizootiology of Trichiniasis in Wildlife  From a Southcentral IoPublished by UNI ScholarWorks, 19601960] TRICIDNIASIS IN WILDLIFE 581 Red fox ( Vulpes fulva) and grey fox ( Urocyon cinereoargen-teus). Foxes examined were primarily red foxes. No attempt was made to differentiate species. During the seven seasons of the study, 431 foxes were examined and 30 (7.0 percent) were found to be infected. A definite downward trend in incidence was noted (Fig-ure 2). During the initial season, 1953-54, 15.5 percent of the 58 foxes examined were infected with T. spiralis. The incidence of infection decreased to 7 .0 percent in 1954-55, followed by 6.9 and 6.6 percent during the 1955-56 and 1956-57 seasons, respectively. No infected foxes were obtained from the study area during the 1957-1958, 1958-59 and 1959-60 seasons. The maximum larval count from foxes was 2 ,000. Two other counts were over 1,000. Fourteen of the 30 infected samples con-tained less than 100 trichinae. Forty-eight fox cubs were examined, with no trichinae being recovered. Mink (Mustela vison). An overall prevalence of 10.1 percent was found in the 198 minks obtained from the study area during the seven seasons. The infective pattern during the first four sea-sons was similar to that found for rats and foxes, i.e. a high initial prevalence followed by a decline (Figure 3). During the first sea-20 18 I 4\ I \ I ' ............... I \ I \ ) \ I \ I ,, 11153-4 1954-5 1955-6 1956-7 1957-8 1958-9 1959-60 TIME INTERVAL Figure 3. Prevalence of trichiniasis in minks. 4Proceedings of the Iowa Academy of Science, Vol. 67 [1960], No. 1, Art. 71https://scholarworks.uni.edu/pias/vol67/iss1/71582 IOWA ACADEMY OF SCIENCE [Vol. 67 son the prevalence was 15 .8 percent, followed by 11.1 percent in 1954-55, and 10.3 percent in 1955-56. No infected minks were obtained in 1956-57. During the next two seasons an upswing in prevalence occurred, rising to 7.4 percent in 1957-58 followed by an additional increase to 18.8 percent in 1958-59. During the 1959-60 season no infected minks were obtained from the study area. The number of larvae recovered from 45-gm. samples of mink was generally high. Only four of the 20 samples from infected ani-mals contained less than 1,000 larvae. Ten of the samples contained more than 10,000 trichinae, the maximum being 57,000. Raccoon (Procyon lotor). Only one (0.5 percent) of the 203 raccoons examined was found to be infected with T. spiralis. The infection was light; 39 trichinae were recovered. No raccoons were obtained during the last two seasons of the study. Badger ( Taxidea taxus). The only badger obtained from the study area was infected with T. spiralis. Nine trichinae were recov-ered from the tissue sample. The badger is the ninth species of wildlife from Iowa which has been found to be infected with this parasite. Other species. In addition to the five species of wildlife which were infected with T. spiralis, other species were examined with negative results. These species, with the number of each examined, are as follows: bat ( 1), beaver ( 7), coyote ( 1), crow ( 20), hawks ( 6), muskrat ( 12 8), opossum ( 60), spotted skunk ( 4) and striped skunk (14). DISCUSSION Although garbage feeding is at a minimum in the corn belt area, the finding of five wildlife species infected with T. spiralis from a limited area in southcentral Iowa emphasizes the problems to be faced before this parasite can be eliminated as a human health hazard. Earlier studies found infected wildlife in all the ten areas of Iowa which were checked. This indicates that trichiniasis in wildlife is not a limited problem, but one in any area which harbors wildlife. It is impossible, from both a practical and conservation standpoint, to attempt to eliminate all wildlife species which may be reservoirs of trichinae. Although the rats examined from this area were all dump rats, the high incidence tends to stress the importance of rats as potential vectors of trichiniasis to grain-fed swine. Rats are present on nearly all Iowa farms. Infected rats could be the source of T. spiralis in swine either through consumption of rats by pigs or by fecal trans-mission. Any infected rat carcass in a swine maintenance area 5Zimmermann et al.: Epizootiology of Trichiniasis in Wildlife  From a Southcentral IoPublished by UNI ScholarWorks, 19601960] TRICHINIASIS IN WILDLIFE 583 could be the source of infection for one or more pigs. Therefore, even on farms where rat control measures are applied, all dead rats should be removed from areas to which swine have access. This would apply also to mice. The possibility of rat or mouse fecal transmission should also be considered. Rats or mice may defecate in swine feeding areas. Fecal contamination of stored swine feed may also occur. Foxes may also have a role in the perpetuation of trichiniasis in grain-fed swine through the medium of feces. Foxes are habitual wanderers at night, sometimes entering hog lots. Although there is a relatively high incidence of trichiniasis in minks, they are less apt to be found in swine feeding areas. The relatively low preva-lence in raccoons would lessen their importance. A larger sample of badgers is needed before their importance can be determined. A rather similar pattern of infection was found in the rat, mink, and fox. There was a high initial prevalence followed by a rather marked decline. The marked decline in rats during the twenty-two month interval between the first and second samplings indicates a decrease in number of viable trichinae present in garbage. This may be partially a reflection of the regulations governing the feeding· of garbage which became effective in nearly all states during the 1953-55 period. This would also tend to explain in part the decline of trichiniasis in fox and mink. Although garbage would be only a minor portion of their diet, they do eat numerous garbage-feeding rodents. There is an indication of a cyclic pattern of infection in mink (Figure 3). The reason for this is unknown, but it may reflect cyclic changes in the population of small rodents. Literature Cited Zimmermann, W. J., Hubbard, E. D., and Biester, H. E. 1959. Studies on trichiniasis in Iowa wildlife (1955-56 and 1956-57 seasons). J. Parasit. 45: 87-90. --, --, and Mathews, J. 1959. Studies on fecal transmission of TrichineUa spiralis. J. Parasit. 45: 441-445. --, Schwarte, L. H., and Biester, H. E. 1956. Incidence of trichiniasis in swine, pork products and wildlife in Iowa. Am. J. Pub. Health 46: 313-319. 6Proceedings of the Iowa Academy of Science, Vol. 67 [1960], No. 1, Art. 71https://scholarworks.uni.edu/pias/vol67/iss1/71

Epizootiology of Trichiniasis in Wildlife  From a Southcentral Iowa Area

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Epizootiology of Trichiniasis in Wildlife From a Southcentral Iowa Area

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