THE OCCURRENCE of HYPODERMA LARVAE in the SPINAL CANAL of CATTLE » by WABREN O

THE OCCURRENCE OF HYPODERMA LARVAE IN THE SPINAL CANAL OF CATTLE » By WABREN O. HABERMAN, instructor of veterinary science and economic entomology. BANNER BILL MORGAN, associate professor of veterinary science, and ROBERT J. DICKE, assistant'¿ professor of economic entomology, Wisconsin Agricultural Experiment Station

INTRODUCTION Little is known of the migratory route of Hypoderma bovis (li.) larvae in cattle. The absence of larval traces from the point of skin penetration to the various positions from which the larvae have been recovered has made this problem difficult. The occurrence of Hypo- derma larvae in the spinal canal of cattle has been recorded on numerous occasions since its discovery by Hinrichsen (4) in 1888 in Germany. However, few observations have been made in North America. The purpose of this paper is to present our observations on Hypoderma larvae in the spinal canal of cattle killed in Wisconsin. Prior to the work of Laake (IS) on the differentiation of Hypoderma lineatum (Villers) and H. bovis, investigators were uncertain about the identity of the first-stage larvae. As suggested by Bishopp et al. (i), many of the previous reports dealing with the occurrence of H. bovis in the esophageal region must be considered in error. Consequently, the identity of larvae in the spinal canal mentioned in reports prior to 1921 is questionable. Hinrichsen (4, 5, 6) apparently found the first stage larvae of Hypoderma bovis in the spinal canal. He reported finding up to 20 larvae in a single animal. Of 25 animals examined, 40 percent had larvae in the spinal canal. A later examination of 14 animals revealed that 28 percent were infested. The larvae appeared to be numerous between December and March. Home (7), unaware of Hinrichsen's earlier work, encountered, in the spinal canal of Norwegian cattle, Hypoderma larvae which he assumed to be H, bovis. Ruser (7, 8) in Germany reported the presence of as many as 20 larvae in the spinal canal of 1 animal. Schneidemühl (20) frequently discovered larvae in the epidural fatty tissue between February and April. Koorevaar (10, 11) in Holland also recorded Hypoderma larvae in the spinal canal of cattle ; in 1 young animal 57 larvae were collected. In experimental transplantation of 26 larvae in a dog, 2 larvae were recovered 14 days later from the spinal canal. Koch (9) in 1903 observed larvae in the spinal canal of cattle between the months qi December to March in Denmark; similar results were obtained bjr Jost (8) in Germany. Peter (15) working in Germany concluded tliat the number of larvae in the spinal canal was usually small, but in the case of 1 bull 62 larvae were observed. The 30 larvae collected by Bishopp et al. (1) from the spinal canal of New York cattle where both species are present, were identified as

1 Received for publication February 17, 1949. Published with the approval of the Director of the Wisconsin Agricultural Experiment Station. Projects No. 596, Economic parasites of livestock; and No. 633, Entomological problems affecting dairying, including insect pests or both dairy animals and dairy produce.

Journal of Agricultural Research Vol. 78, No. 12 Washington, D. C. June 15, 1949 (637) Key No. Wis.—179 638 Journal of Agricultural Research Vol. 78, No. 12

Hypoderma hovis, while only a single specimen was found in Texas cattle where only H, lineatum occurs. Mote (14) in Ohio reported 6 H, boms larvae in the spinal canal of a cow. In France, Popesco- Baran (16) foimd 15 larvae in the spijial canal of an 8-to-lO-month-old calf. Schmid (19) reported that 4 of 68 animals in Germany were infested. The following year 10 larvae were located in the spinal canal of a bull. Soni (^1) recorded the occurrence of larval H, lineatum in the spinal canal of cattle in India. Gebauer (3)j working in Germany, reported finding larval traces in the epineural connective tissue of 2 calves. Three H, boms larvae were found associated with the characteristic greenish extraneous material present along the nerve trunks from the foot to the spinal canal. The more than 20 larvae removed from the spinal canals were H. boms. The most comprehensive work to date was done by Eichler (;^) in 1941 in Ger- many. All the larvae identified of the 189 collected from the spinal canal were H, boms. He also identified as H. boms 11 of 36 larvae, which were collected by Staack in 1938. Kurtpinar (12), working in Turkey, where only H. bovis is found, frequently observed the larvae in the canalis vertebralis.

MATERIALS AND METHODS The fatty connective tissue which lies between the periosteum and dura mater in the spinal canal was removed from cattle slaughtered at a local abattoir and taken to the laboratory for examination. Material was collected on the cattle-killing floor; facilities were made available through th^ courtesy of the Oscar Mayer Packing Co.,

TABLE 1.—Summary of collections of Hypoderma larvae f rom the spinal canals of 293 cattle

Average length Larvae present Aver- Size range of larvae of larvae Spinal Spinal age Period of examination canals canals larvae exam- in- H, per H. ined fested H. line- canal H. line- line- bovis atum bovis atum bovis atum

Num- Num- Num- Num- Num- Milli- Milli- Milli- Milli- m7 ber ber ber ber ber meters meters meters meters February 20 5 11 2.2 11.0-14.0 12.7 March 95 9 21 2.3 11.0-16.0 13.6 April 1150 4 4 1.0 14.0-15.0 14.7 May 1170 2 5 2.5 15.0-16.5 15.6 JllTlft 1185 0 July - 70 0 August 180 0 September 150 0 October... __ 140 0 November 185 5 33 -- 6.6 5.0-11.0 8.1 December 190 6 10 1.7 7.0-14.5 14.0-14.5 9.3 14.2 m8 January, _ _ 185 41 153 3.7 5.0-16.0 11.7 February 275 107 497 4.6 7.0-17.0 14.0-15.5 12.2 14.7 March _ ___ 328 76 146 1.9 8.0-16.0 12.9 April 165 22 58 2.6 8.6-16.0 12.4 May 65 1 1 1.0 15.0 15.0 June.. _ 105 0 July 50 0 August 255 0 September 250 1 1 1.0 7.5 7.5 October _ _ 335 14 35 2.5 5.5-13.0 8.1

«Approximate number of spinal canals examined. June 15,1949 Hypoderma Larvae in the Spinal Canal of Cattle 639

Madison, Wis. Samples of tissue from each spinal canal were macer- ated with forceps and examined closely for the presence of larvae. These were examined microscopically either as living or in the pre- served state. Identifications were based on differences in the cephalopharyngeal skeleton of the first stage larvae (Jf^). The results of this investiga- tion are shown in table 1. RESULTS Of 982 larvae removed from 293 infested spinal canals, 975 were identified as Hypoderma hovis and 7 as H, lineatum. The maximum number of larvae removed from a single infected spinal canal was 21. The length of the larvae ranged from 5.0 to 17.0 mm., and a progres- sive increase in the average length was noted from September (7.5 mm.) to May (15.6 mm.). Both species of the warble fly, Hypoderma hovis and H, lineatum, were present in this area (Wisconsin), but H, hovis was found to be the most abundant. However, this work included examinations of animals from other areas where H. lineatum is more prevalent. An examination of a comparable group of animals during the same period indicated a prevalence of Hypoderma larvae in the esophageal region. Of 982 larvae removed from infested esophagi, 981 were fir. lineatum and only 1 was H. hovis,

SUMMARY Our observations on the occurrence of Hypoderma hovis in the spinal canal of cattle indicated a distinct difference in the migration route followed by the larvae of the two species. Only the larvae of H, hovis occurred regularly in the spinal canal whereas those of H, lineatum were rarely found in the spinal canal. On the other hand, only fir. lineatum occurred regularly in the esophageal region. The increase in the average length of the larvae and in the number collected between September and June indicated that the larvae gradually accumulate in this region prior to appearing in the subdermal regions of the back. This occurrence corresponds with the well-known accumidation of H. lineatum larvae in the submucosa of the esophagus.

LITERATURE CITED

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