The Helminthological Society of Washington

SUMMARY AND CONCLUSIONS In limited anthelmintic studies with toluene and some of its halogen substitution products, namely, the ortho-, meta-, and para-isomers of chloro-, bromo-, iodo-, and fluoro-toluene, and 2 di-substituted derivatives, namely, 2,6-dichlorotoluene and 2,5-dibromotoluene, it was found that the introduction of halogens into the ring usually caused a reduction in efficacy . In general, the dimunition was more pronounced with hookworms than with ascarids, and it was considerably greater with the di-substituted products than with the corresponding mono-halogenated compounds . At a dose rate of 0 .1 cc . per pound of body weight, toluene removed 100 per cent of 61 ascarids from 2 dogs, 99 per cent (349) of 351 hookworms from 4 dogs, and 75 per cent (121) of 161 whipworms from 6 dogs . The most effective substitution product, o-chlorotoluene, removed 100 per cent of 66 ascarids from 2 dogs, and 96 per cent (484) of 499 hookworms and 92 per cent (166) of 179 whipworms from 4 dogs. Comparable ascaricidal action was exhibited by m-chlorotoluene and m-fluorotoluene, and o-bromotoluene and p-fluorotoluene removed significant numbers of hookworms . In the aggregate, the chloro-, bromo-, and fluorotoluenes were about equally effective against ascarids ; th iodotoluenes, however, were significantly less effective than the other halogenated compounds . With respect to hookworms, the chlorotoluenes were most effective, followed in order by the bromo-, fluoro-, and iodo-toluenes . In considering the aggregate efficacy of the mono-halogenated compounds, the meta-position appeared to be the most favorable site for halogenation, and the para-position appeared to be least favorable in this respect . Diagnosis of gastrointestinal nematode parasitism of sheep by differential egg counts. K . C. KATES, U. S. Bureau of Animal Industry . Gastrointestinal parasitism of sheep is of common occurrence in the United States, affected sheep usually harboring several different genera and species of helminths . These helminths differ markedly in their effect on the host, and a reasonably accurate knowledge of both kinds and numbers of helminths present is, therefore, desirable . At present two methods of securing that knowledge, at least in part, are available. One consists in slaughtering some affected animals in a flock and collecting and counting the helminths present in the alimentary tract. This method is accurate so far as the individual animal examined at necropsy is concerned, but it is only indicative with respect to the remaining animals in the flock. The other method consists in the examination of droppings, for helminth eggs, of a number of animals in the flock . This method may have two advantages over the slaughter method in that (a) no animals are lost by slaughter, (b) many more animals can be examined and, therefore, a better estimate of the helminth population of the flock as a whole can be obtained . Qualitative differential diagnosis of gastrointestinal parasitism in sheep by fecal examination for eggs has been shown to be a practical procedure, with some limitations, by Shorb (1939, 1940) and Kates and Shorb (1943) . Little information is available, however, concerning the practical application of differential egg counts to quantitative diagnosis of helminths in sheep . The problem of determination of genera and species of adult helminths present in the alimentary tract by fecal examinations for eggs is the relatively simple one of differentiating the eggs of the various genera or species by means of structural, color, and size differences . Accuracy of these determinations is limited mainly by the presence or absence of recognizable differences in eggs of various species . In contrast, in any attempt to correlate differential egg counts with the number of parasites present in the host, certain complicating factors must be taken into consideration in order properly to evaluate the data . Some of these factors are :' (1) Differences in egg-producing capacity of various species of helminths . (2) Variations in egg production within the species because of variations in size of infestation, diet of host, age of parasites, age of host, etc . (3) Variations in resistance of host to various species of helminths. (4) Sex ratio of parasites . (5) Physical condition of stool . 11 am indebted for some helpful suggestions in this connection to a manuscript of an address delivered by Dr. A . O. Foster before the Medical Association of the Isthmian Canal Zone on August 4, 1938, entitled : "Factors affecting egg-worm ratios in hookworm infections ." The purpose of this paper is to present data showing some aspects of the utility and limitations of differential egg counts in the quantitative determination of gastrointestinal nematode populations of lambs . These data were collected at the Zoological Division, Agricultural Research Center, U. S. Department of Agriculture, Beltsville, Md., over a considerable period and the observations recorded were incidental to other investigations on sheep parasites . Although a special situation is represented here, it is thought that it may be representative of some situations encountered in the field.