Epidemiological studies on gasterophiliasis in Kyushu, Japan : results of surveys on carcases

Infestation of Gasterophilus larvae to stomach (including original part of duodenum) was investigated for 1968-1971 with a total of 1,009 slaughtered horses at the abattoirs in 4 cities in Kyushu, namely, Kumamoto, Miyakonojo, Beppu and Izuka, and the following knowledge was obtained. 1) Out of 1,009 slaughtered horses, infestation was observed on 309 cases, indicating an average infestation rate of 30.6%. The infestation rate according to the age were as follows: younger than 2 years 28.2% 3-6 years 23.7% 7-10 years 30.1% 11-14 years 40.6% older than 15 years 55.6% Generally a ratio was higher as a horse was older in age. It was however known that even with those horses younger than 2 years, still infestation was found in no small numbers. 2) Those infestant around Pars proventricularis and Margo plicatus (partly across Pars glandularis) are Gasterophilus intestinalis, and those infestant around Pars pylorica and original part of duodenum are Gasterophilus nasalis. The former was found in 91.6% of the total infestation (309 cases), and the latter was seen in 58.9% of them. Furthermore combined infestation of G. intestinalis and G. nasalis was found in 50.6%. No case of G. haemorrhoidalis was found at all. 3) Numbers of larvae found in stomach and duodenum (approximate number) were as follows: Among the total infestation (309 cases) 56.6% had less than 50, 38.2% had 51-300, and only 5.2% had 301 or more. However it varies very much by the season, i. e., generally a good number of larvae are found in winter and spring, it however decreases remarkably in summer and autumn. 4) In Kyushu there are some districts, wherein the horse meat is used for food, for instance, Kumamoto and others. Recently the horse breeding has gradually been declined in Kyushu, therefore, horses for meat are obliged to be brought in from Hokkaido. Numbers of such transfer are increasing year by year, thus at present (1970) about 60% of the slaughtered horses at the Kumamoto abattoir are those brought from Hokkaido. Under such circumstances among the above-mentioned slaughtered horses (1,009 in total) include a good many of those raised in Hokkaido and apparently infestated by Gasterophiliasis there already. 5) The breakdown list of total 1,009 slaughtered horses is as follows: Raised in Kyushu 503 Raised in Hokkaido 402 Raised in others (Chugoku and Shikoku) 16 Unknown 88 As to the rate of infestation, a remarkable difference was observed between the horses raised in Hokkaido and those raised in Kyushu. The rate of the former was 55.2%, while the rate of the latter was only 8.7%. There was no big difference found as per prefectures in Kyushu (Miyazaki, Kagoshima, Oita, Kumamoto, Nagasaki, Fukuoka and Saga). 6) The reason why infestation of Gasterophiliasis is more on horses from Hokkaido and less on horses in Kyushu can be considered as follows: One of the reason is that the horses in Hokkaido are frequently put to pasture, while in Kyushu they are mainly raised inhousing. In view of the life cycle of Gasterophilus it is natural that the former is facing a good many chances of infestation in the field. Another reason is considered to be that throughout the respective growth stage of Gasterophilus (hatching, emergence, imaginal stage, etc.), infestation is easier in the place as Hokkaido where temperature of the air is comparatively low.