出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2013/04/27 13:03:04」(JST)
| Toxocara canis | |
|---|---|
| Adult Toxocara canis | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Nematoda |
| Class: | Secernentea |
| Order: | Ascaridida |
| Family: | Toxocaridae |
| Genus: | Toxocara |
| Species: | T. canis |
| Binomial name | |
| Toxocara canis Werner 1782 |
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Toxocara canis (also known as dog roundworm) is worldwide-distributed helminth parasite of dogs and other canids. T. canis is gonochoristic, adult worms measure from 9 to 18 cm, are yellow-white in color, and occur in the intestine of the definitive host. In adult dogs, the infection is usually asymptomatic. By contrast, massive infection with T. canis can be fatal in puppies.[1][2] As paratenic hosts, a number of various vertebrates, including humans, and some invertebrates can become infected. Humans are infected, like other paratenic hosts, by ingestion of embryonated T. canis eggs.[3] The disease caused by migrating T. canis larvae (toxocariasis) results in two syndromes: visceralis larva migrans and ocularis larva migrans.[4] Owing to transmission of the infection from bitches to puppies, preventive anthelmintic treatment of newborn puppies is strongly recommended. Several antihelmintic drugs are effective against adult worms, for example pyrantel, fenbendazole, selamectine, etc.[5]
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The adult T. canis has a round body with spiky cranial and caudal parts, covered by yellow cuticula. The cranial part of the body contains two lateral alae (length 2–2.5 mm, width 0.2 mm). Male worms measure 9–13 by 0.2–0.25 cm and female worms 10–18 by 0.25–0.3 cm. T. canis eggs have oval or spherical shapes with granulated surfaces, are thick-walled, and measure from 72 to 85 μm.[1]
Four modes of infection are associated with this species. The basic form is typical to all ascaroides, with the egg containing the L2(the second larval developmental stage) being infective, at optimal temperature and humidity, four weeks after secreted in the faeces to the environment. After ingestion and hatching in the small intestine, the L2 larvae travel through the portal blood stream into the liver and lungs. Such migratory route is known as enterohepatic pulmonar larval migration. The second molt takes place in the lungs, the now L3 larvae return via the trachea and into the intestines, where the final two molts take place. This form of infection occurs regularly only in dogs up to three months of age.
In older dogs, this type of migration occurs less frequently, and at six months it is almost ceased. Instead, the L2 travel to a wide range of organs, including the liver, lungs, brain, heart and skeletal muscles, as well as to the walls of the gastrointestinal tract. In pregnant bitches, prenatal infection can occur, where larvae become mobilized (at about three weeks prior to parturition) and migrate to the lungs of the fetus, here molting into the L3 stage just prior to birth. In the newborn pup, the cycle is completed when the larvae migrate through the trachea and into the intestinal lumen, where the final molts take place. Once infected, a bitch will usually harbor sufficient larvae to subsequently infect all of her litters, even if she never again encounters an infection. A certain amount of the bitch's dormant larvae penetrate into the intestinal lumen, where molting into adulthood takes place again, thus leading to a new release of eggs containing L1 larvae.
The suckling pup may be infected by the presence of L3 larvae in the milk during the first three weeks of lactation. There is no migration in the pup via this route. L2 larvae may also be ingested by a variety of animals, where they stay in a dormant stage inside the animals' tissue until the intermediate host has been eaten by a dog, where subsequent development is confined to the gastrointestinal tract.[6]
Humans can be infected by this roundworm, a condition called toxocarosis, just by stroking an infected dog's fur. In humans, this parasite usually grows in the back of the eye, which can result in blindness, or in the liver or lungs.[7] However, a 2004 study showed, of 15 infected dogs, only seven had eggs in their coats, and no more than one egg was found on each dog. Furthermore, only 4% of those eggs were infectious.[8] Given the low concentration of fertile eggs on infected dogs' coats (less than 0.00186% per gram), it is plausible that such eggs were transferred to the dog's coat by contact with fecal deposites in the environment, making dog coats the passive transport hosts.[8]
The risk of being infected by petting a dog is extremely limited and, since a single infected puppy can produce more than 100,000 roundworm eggs per gram of feces,[9] humans are much more likely to be infected by contact with feces than contact with fur. As such, little reason exists for humans to fear infection, as long as basic hygiene, such as hand-washing, is followed.[7]
Several treatments, all of which are cheap and easily accessible by the average dog owner, can prevent a dog from becoming infected or rid an infected pet of its roundworm parasites.
Visceral toxocariasis in humans (or dogs) can be treated with antiparasitic drugs such as albendazole or mebendazole, usually in combination with anti-inflammatory medications. Treatment of ocular toxocariasis is more difficult and usually consists of measures to prevent progressive damage to the eye.
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| リンク元 | 「蠕虫」 |
| 関連記事 | 「can」「Toxocara」「Canis」 |
| 蠕虫類 | 病原体名 | 病名 | 感染経路 | 寄生部位 | 症状 | 診断 | 治療 | |
| 線虫類 | Ancylostoma duodenale | ズビニ鉤虫 | 鈎虫症/十二指腸虫症 | F型幼虫経口感染、経皮 | 空腸上部 | 皮膚炎、若菜病、貧血 | 飽和食塩水浮遊法、遠心沈降法 | pyrantel pamoate、鉄剤 |
| Necator americanus | アメリカ鉤虫 | |||||||
| Strongyloides stercoralis | 糞線虫 | 糞線虫症 | F型幼虫経皮感染 | 小腸上部 | Loffler症候群 | 糞便塗沫、普通寒天平板培養による R型、F型幼虫の検出 |
thiabendazole, ivermectin | |
| Enterobius vermicularis | 蟯虫 | 蟯虫症 | 虫卵経口感染 | 盲腸～大腸 | 夜間の掻痒、不眠、情緒不安定 | 肛囲検査法「柿の種」 | pyrantel pamoate | |
| Ascaris lumbricoides | 回虫 | 回虫症 | 虫卵経口感染 | 小腸孵化→門脈→ 肺発育→食道嚥下→小腸 |
Loffler症候群。急性腹痛 | 糞便虫の虫卵の証明 | pyrantel pamoate | |
| Toxocara canis | イヌ回虫 | 幼虫移行症 | 生後1-2ヶ月の感染犬の 糞から経口感染 |
なし | 幼虫移行症→失明 | 免疫診断 | 治療法無し？ | |
| Wuchereria bancrofti | バンクロフト糸状虫 | フィラリア症/糸状虫症 | アカイエカ | リンパ系 | 急性期：リンパ肝炎、リンパ腺炎を伴う熱発作(filarial fever) 慢性期：乳糜尿、リンパ管瘤、陰嚢水腫、象皮病 |
急性期：夜間のmicrofilariaの検出 慢性期：特有の症状を考慮 |
diethylcarbamazine & ivermectin | |
| Brugia malayi | マレー糸状虫 | |||||||
| Dirofilaria immitis | イヌ糸状虫 | アカイエカ | なし | 幼虫移行症→肺血管閉塞→胸部X線画像銭形陰影 | ||||
| Gnathostoma spinigerum | 有棘顎口虫 | 顎口虫症 | ドジョウ、雷魚、ヘビの生食 | 消化管壁貫通→皮下移動による腫瘤や線状皮膚炎 | 移動性腫瘤、皮膚爬行疹 雷魚やドジョウの生殖の問診 免疫血清診断 |
なし | ||
| Gnathostoma hispidum | 剛棘顎口虫 | |||||||
| Gnathostoma doloresi | ドロレス顎口虫 | |||||||
| Gnathostoma nipponicum | 日本顎口虫 | |||||||
| Anisakis simplex, larva | アニキサス幼虫 | アニサキス症 (1)胃アニサキス症、 (2)腸アニサキス症、 (3)異所性アニサキス症 |
経口感染 終宿主：クジラ、イルカ。 中間宿主：オキアミ。 待機宿主：サバ、ニシン、アジ、タラなど |
胃や腸 | (1)急激な上腹部痛"胃けいれん" (2)腹痛、急性虫垂炎、イレウス様。劇症型と緩和型がある (3)腹腔内の炎症性肉芽腫 |
胃内視鏡検査 | 内視鏡による虫体摘出 | |
| Pseudoterranova decipiens | ||||||||
| Trichinella spiralis | 旋毛虫 | 旋毛虫症 | 経口感染 豚肉、クマ肉の生食 |
(1)成虫侵襲期：下痢、腹痛 (2)幼虫筋肉移行期：顔面浮腫、心筋障害など (3)幼虫被嚢期：全身浮腫、衰弱 |
急性期：ステロイド 殺虫：mebendazole | |||
| 鞭虫症 | 盲腸 | 慢性下痢、腹痛、異食症、貧血 | セロファン重層塗沫法、 ホルマリンエーテル法 |
mebendazole | ||||
| Spirurin nematode larva | 旋尾線虫 | 旋尾線虫幼虫 | ホタルイカの生食 | なし | 皮膚爬行疹、イレウス様症状 | 予防：-30℃24時間。 生食には-30℃4日間以上 |
摘出 | |
| 吸虫類 | Shistosoma japonicum | 日本住血吸虫 | 日本住血吸虫症 | 糞便虫の虫卵→ミラシジウム→ ミヤイリガイ体内でセルカリア→ 人畜の皮膚より浸入→循環系→ 門脈に寄生 |
門脈 | (1)潜伏期：侵入部の掻痒性皮膚炎。肺移行期：咳、発熱 (2)急性期：虫卵の門脈系寄生、産卵。住血吸虫性赤痢。 (3)慢性期：虫卵の肝、脳などの塞栓。肝硬変。脾腫、腹水 |
糞便虫の虫卵の検出。 直腸粘膜層掻爬法、 肝穿刺による組織内虫卵の検出。 補助診断として免疫血清学的検査。 |
praziquantel |
| Paragonimus westermani | ウェステルマン肺吸虫 | 肺吸虫症/肺ジストマ症 | 経口感染 淡水産のカニ、イノシシ肉の生食 |
肺 | 痰、咳、胸痛、時に喀血 | 痰や便の虫卵検査、 胸部写真、 断層写真で明らかな虫嚢。 免疫学血清検査 |
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| Paragonimus miyazakii | 宮崎肺吸虫 | 肺 | 気胸、胸水貯留、膿胸、好酸球増加 | praziquantel | ||||
| Clonorchis sinensis | 肝吸虫 | 肝吸虫症/肝ジストマ症 | 経口感染 虫卵→(マメタニシ:セルカリア)→ セルカリア→(魚:メタセルカリア)→ 摂取→(ヒト:成虫)→虫卵 |
胆管 | 胆汁流出障害による肝障害→肝硬変 | 糞便、胆汁(十二指腸ゾンデ法)。 肝吸虫卵の検出。CT像。エコー検査。 |
praziquantel | |
| 横川吸虫症 | 淡水魚(アユ、フナ、ウグイ、シラウオ)の生食 | 小腸粘膜 | 下痢、腹痛 | 糞便虫の虫卵 | praziquantel | |||
| 条虫類 | Taeniarhynchus saginatus | 無鉤条虫 | 腸管条虫症 | 経口感染。中間宿主：ウシ | 小腸 | 無症状。下痢。 広節裂頭条虫感染では悪性貧血。 |
糞便虫の虫卵と体節により診断 | praziquantel。 有鉤条虫の場合はガストログラフィン。 有鉤条虫の駆虫の際、 虫体を破壊しない →虫体の融解による嚢虫症 |
| Taenia solium | 有鉤条虫 | 経口感染。中間宿主：ブタ | ||||||
| Diphyllobothrium latum | 広節裂頭条虫 | 経口感染。中間宿主：サケ、マス | ||||||
| 日本海裂頭条虫 | 経口感染。中間宿主：サケ | |||||||
| 腸管外条虫症 | ||||||||
| 有鉤嚢虫症 | 有鉤条虫の虫卵の経口摂取 | 皮下、筋肉内 脳、脊髄、眼球 |
皮下、筋肉内：小指頭大の無症状腫瘤 脳、脊髄、眼球：Jacksonてんかん。痙性麻痺など |
皮下の虫嚢 | 外科的摘出。 成虫寄生がなければ、praziquantel, albendazole + ステロイド | |||
| Echinococcus granulosus | 単包虫 | 包虫症/ エキノコックス症 (単包虫症) |
終宿主：イヌ、キツネなど。 中間宿主：ヒト、ブタ、野ネズミなど。 終宿主の糞便虫の虫卵を中間宿主が接種して発症 |
肝、肺、まれに脳、腎、筋肉 | 肝寄生：肝部疼痛、満腹、時に黄疸、下肢浮腫 肺寄生：胸部圧迫感、胸痛、咳、血痰、時に喀血 |
肝や肺の嚢胞形成から疑う。 早期に診断に皮内反応→ CT、エコー→ 生検。免疫血清学的診断法 |
外科的切除。 albendazoleの長期投与 | |
| Echinococcus multilocularis | 多包虫 | 包虫症/ エキノコックス症 (多包虫症) | ||||||