出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2015/05/13 12:27:53」(JST)
| Pinworm
ICD-9 127.4, ICD-10 B80 |
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| Pinworms(U.S.)/Threadworms(U.K.) (Enterobius vermicularis). | |
| Scientific classification | |
| Kingdom: | Animalia |
| Phylum: | Nematoda |
| Class: | Secernentea |
| Subclass: | Spiruria |
| Order: | Oxyurida |
| Family: | Oxyuridae |
| Genus: | Enterobius |
| Species | |
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The pinworm (genus Enterobius), also known as threadworm (in the United Kingdom and Australia) or seatworm, is a parasitic worm. It is a nematode (roundworm) and a common intestinal parasite or helminth, especially in humans.[5] The medical condition associated with pinworm infestation is known as enterobiasis[6] (a type of helminthiasis) or less precisely as oxyuriasis in reference to the family Oxyuridae.[7]
Throughout this article, the word "pinworm" refers to Enterobius. In British usage, however, pinworm refers to Strongyloides, while Enterobius is called threadworm.[8]
The pinworm (genus Enterobius) is a type of roundworm (nematode), and three species of pinworm have been identified with certainty.[9] Humans are hosts only to Enterobius vermicularis (formerly Oxyurias vermicularis).[10] Chimpanzees are host to Enterobius anthropopitheci, which is morphologically distinguishable from the human pinworm.[3] Hugot (1983) claims there is another species affecting humans, Enterobius gregorii, which is supposedly a sister species of E. vermicularis, and has a slightly smaller spicule (i.e., sexual organ).[11] Its existence is controversial however; Totkova et al. (2003) consider there to be insufficient evidence,[4] and Hasegawa et al. (2006) contend that E. gregorii is a younger stage of E. vermicularis.[2][3] Regardless of its status as a distinct species, E. gregorii is considered clinically identical to E. vermicularis.[10]
The adult female has a sharply pointed posterior end, is 8 to 13 mm long, and 0.5 mm thick.[12] The adult male is considerably smaller, measuring 2 to 5 mm long and 0.2 mm thick, and has a curved posterior end.[12] The eggs are translucent[12] and have a surface that adheres to environmental objects.[13] The eggs measure 50 to 60 μm by 20 to 30 μm, and have a thick shell flattened on one side.[12] The small size and colourlessness of the eggs make them invisible to the naked eye, except in barely visible clumps of thousands of eggs. Eggs may contain a developing embryo or a fully developed pinworm larva.[12] The larvae grow to 140–150 μm in length.[13]
The pinworm has a worldwide distribution,[14] and is the most common helminth (i.e., parasitic worm) infection in the United States, western Europe, and Oceania.[15][16] In the United States, a study by the Center of Disease Control reported an overall incidence rate of 11.4% among people of all ages.[16] Pinworms are particularly common in children, with prevalence rates in this age group having been reported as high as 61% in India, 50% in England, 39% in Thailand, 37% in Sweden, and 29% in Denmark.[16] Finger sucking has been shown to increase both incidence and relapse rates,[16] and nail biting has been similarly associated.[17] Because it spreads from host to host through contamination, pinworms are common among people living in close contact, and tends to occur in all people within a household.[14] The prevalence of pinworms is not associated with gender,[14] nor with any particular social class, race, or culture.[16] Pinworms are an exception to the tenet that intestinal parasites are uncommon in affluent communities.[16] The earliest known instance of the pinworms associated with humans is evidenced by pinworm eggs found in coprolite, carbon dated to 7837 BC at western Utah;[13] however 240 million years ago parasitic pinworm nematodes already infested pre-mammalian cynodonts: a fossilized egg was detected in fossil dung.[18]
The entire lifecycle, from egg to adult, takes place in the human gastrointestinal tract of a single human host,[12][13] from about 2–4 weeks[19] or about 4–8 weeks.[16]
The lifecycle begins with eggs being ingested.[13] The eggs hatch in the duodenum (i.e., first part of the small intestine).[20] The emerging pinworm larvae grow rapidly to a size of 140 to 150 μm,[19] and migrate through the small intestine towards the colon.[13] During this migration, they moult twice and become adults.[13][16] Females survive for 5 to 13 weeks, and males about 7 weeks.[13] The male and female pinworms mate in the ileum (i.e., last part of the small intestine),[13] whereafter the male pinworms usually die,[20] and are passed out with stool.[21] The gravid female pinworms settle in the ileum, caecum (i.e., beginning of the large intestine), appendix and ascending colon,[13] where they attach themselves to the mucosa[16] and ingest colonic contents.[14]
Almost the entire body of a gravid female becomes filled with eggs.[20] The estimations of the number of eggs in a gravid female pinworm range from about 11,000[13] to 16,000.[16] The egg-laying process begins about five weeks after initial ingestion of pinworm eggs by the human host.[13] The gravid female pinworms migrate through the colon towards the rectum at a rate of 12 to 14 cm per hour.[13] They emerge from the anus, and while moving on the skin near the anus, the female pinworms deposit eggs either through (1) contracting and expelling the eggs, (2) dying and then disintegrating, or (3) bodily rupture due to the host scratching the worm.[20] After depositing the eggs, the female becomes opaque and dies.[21] The reason the female emerges from the anus is to obtain the oxygen necessary for the maturation of the eggs.[21]
E. vermicularis causes the medical condition enterobiasis, whose primary symptom is itching in the anal area.[22] Albendazole or mebendazole is the first-line treatment of pinworm infection. Pyrantel pamoate is alternative.
Pinworms spread through human-to-human transmission, by ingesting (i.e., swallowing) infectious pinworm eggs and/or by anal insertion.[16][20] The eggs are hardy and can remain viable (i.e., infectious) in a moist environment up to three weeks.[16][21] They do not tolerate heat well, but can survive in low temperatures: two-thirds of the eggs are still viable after 18 hours at −8 °C (18 °F).[21]
After the eggs have been initially deposited near the anus, they are readily transmitted to other surfaces through contamination.[20] The surface of the eggs is sticky when laid,[13][21] and the eggs are readily transmitted from their initial deposit near the anus to fingernails, hands, night-clothing and bed linen.[19] From here, eggs are further transmitted to food, water, furniture, toys, bathroom fixtures and other objects.[13][16][20] Household pets often carry the eggs in their fur, while not actually being infected.[23] Dust containing eggs can become airborne and widely dispersed when dislodged from surfaces, for instance when shaking out bed clothes and linen.[16][21][23] Consequently, the eggs can enter the mouth and nose through inhalation, and be swallowed later.[16][19][20][21] Although pinworms do not strictly multiply inside the body of their human host,[19] some of the pinworm larvae may hatch on the anal mucosa, and migrate up the bowel and back into the gastrointestinal tract of the original host[16][19] in a process called retroinfection.[16][21] When this retroinfection occurs, it can lead to a heavy parasitic load and ensures the pinworm infestation continues[16] or can be not clinically significant.[21] Despite the limited, 13-week lifespan of individual pinworms,[13] autoinfection (i.e., infection from the original host to itself), either through the anus-to-mouth route or through retroinfection, usually necessitates repeated treatment, at 2-week intervals, in order to remove the infection completely.[24]
Pinworms are sometimes diagnosed incidentally by pathology. Micrograph of pinworms in the appendix, H&E stain
High magnification micrograph of a pinworm in cross section in the appendix, H&E stain
Egg under a light microscope
Pinworms are sometimes diagnosed incidentally by pathology: Micrograph of male pinworm in cross section, alae (blue arrow), intestine (red arrow) and testis (black arrow), H&E stain
Pinworm eggs are easily seen under a microscope.
This micrograph reveals the cephalic alae in the head region of E. vermicularis.
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| リンク元 | 「蠕虫」「蟯虫」「Oxyuroidea」「pinworm」「ギョウチュウ」 |
| 関連記事 | 「Enterobius」 |
| 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) | ||||||
蟯虫、蟯虫類、エンテロビウス、ョウチュウ属、エンテロビウス属、Enterobius属