九州におけるウマバエ症の疫学的研究と畜体についての調査成績

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　昭和43～46年,九州内の熊本･都城･別府･飯塚の4と畜場において合計1,009頭のと殺馬の胃(十二指腸起始部を含む)を検査し,ウマバエ幼虫の寄生状態を観察して以下の知見を得た.　1) 調査馬合計1,009頭中309例にウマバエ幼虫の寄生を認めた.すなわち平均寄生率は30.6%である.年令別にみると2才以下の寄生率は28.2%,3～6才は23.7%,7～10才は30.1%,11～14才は40.6%,15才以上は55.6%であり,一般に年令の進むほど寄生率は高くなる. しかし2才以下の若令馬にも少なからざる寄生を認めた.　2) 胃のうち前胃部およびヒダ状緑付近に寄生する種類は Gasterophilus intestinalis で,胃の幽門部および十二指腸起始部に寄生するのは Gasterophilus nasalis である. 前者は寄生例全体(309例)の91.6%に見られ,後者は58.9%に認められた. 両種類が同時に寄生するものは50.6%であった.なお Gasterophilus haemorrhoidalis は1例も認めなかった.　3) 胃と十二指腸を合わせた寄生数(概数)は,50匹以下が寄生例全体(309例)の56.6%で半数以上を占め,51～300匹が38.2%,301匹以上のケースは5.2%であった. ただし寄生数は季節による変動が著しく,一般に冬･春季に多数寄生するものも夏･秋季には激減する.　4) 九州では熊本その他で馬肉を好んで食する地域がある. 九州の馬の飼育頭数は漸減の傾向にあるので,いきおい食肉用の馬をわが国の馬の多産地である北海道から搬入する. その数は年々増加し,熊本市食肉センターでは昭和45年におけると殺馬の約60%は北海道馬で占められた. このような状況下, 上述の調査馬(1,009頭)のなかには北海道で飼育され, ウマバエの感染が北海道で起きたことの明白なものが相当多数含まれている.　5) すなわち, 1,009頭の調査馬の産地区分は九州産が503頭,北海道産が402頭,その他(中国･四国など)16頭,産地不明88頭であった. このうち北海道馬と九州馬のウマバエ寄生率を比較すると,前者が55.2%とすこぶる高値であるのに対し,後者(九州馬)のそれはわずか8.7%で著しく低い. 次に九州内の各県(宮崎･鹿児島･大分･熊本･長崎･福岡･佐賀)の間には著差は認められない(県によっては例数が少なくて比較不能).要するに九州馬そのもののウマバエ寄生率は一般に低いが, 外部から搬入された馬(北海道馬)によって平均寄生率がかなり上昇するという疫学上特異のパターンを示している.　6) 北海道馬にウマバエ寄生が多く九州馬に少ない理由の第一は, 北海道馬は放牧の機会が多いのに対し九州馬の飼育形態は主として舎飼いであるためであろう. ウマバエの発育環からみて野外における感染のチャンスが多いのは当然である. 第二の理由としてウマバエの発育の各ステージ(卵のふ化,サナギの羽化,成虫期など)を通じ,外界の気温の高いところよりも東北･北海道のごとき比較的低温な地方が適しているためと思われる.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 88As 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.
宮崎大学農学部の論文

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芦沢広三
宮崎大学農学部家畜病理学教室

九州におけるウマバエ症の疫学的研究と畜体についての調査成績

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九州におけるウマバエ症の疫学的研究 と畜体についての調査成績

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九州におけるウマバエ症の疫学的研究と畜体についての調査成績