Necator americanus

日

アメリカ鉤虫

同

New World hookworm

関

hookworm

WordNet

1. infestation of the intestines by hookworms which enter the body (usually) through the skin (同)hookworm_disease
2. parasitic bloodsucking roundworms having hooked mouth parts to fasten to the intestinal wall of human and other hosts

PrepTutorEJDIC

1. 十二指腸虫 / 十二指腸虫症

Wikipedia preview

出典(authority):フリー百科事典『ウィキペディア（Wikipedia）』「2014/11/05 17:49:14」(JST)

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Necator americanus
Scientific classification
Kingdom:	Animalia
Phylum:	Nematoda
Class:	Secernentea
Order:	Strongylida
Family:	Ancylostomatidae
Genus:	Necator
Species:	N. americanus
Binomial name
Necator americanus

Necator americanus is a species of hookworm commonly known as the New World hookworm. Like other hookworms, it is a member of the phylum Nematoda. It is a parasitic nematode that lives in the small intestine of hosts such as humans, dogs, and cats. Necatoriasis is the term for the condition of being host to an infestation of a species of Necator. Since N. americanus and Ancylostoma duodenale (also known as Old World hookworm) are the two species of hookworms that most commonly infest humans, they are usually dealt with under the collective heading of "hookworm infection". They differ most obviously in geographical distribution, structure of mouthparts, and relative size.

Necator americanus has been proposed as an alternative to Trichuris suis in helminthic therapy.

Morphology

This parasite has two dorsal and two ventral cutting plates around the anterior margin of the buccal capsule. It also has a pair of subdorsal and a pair of subventral teeth located close to the rear. Males are usually 7-9 mm long, whereas females are about 9-11 mm long. The typical lifespan of these parasites is three to five years. They can produce between 5000 and 10,000 eggs per day.

Lifecycle

Lifecycle of a hookworm

Cutaneous larvae migrans

This worm starts out as an unembryonated egg in the soil. After 24–48 hours under favorable conditions, the eggs become embryonated and hatch. This first juvenile stage 1 is known as 'rhabditiform'. The rhabditiform larvae grow and molt in the soil, transforming into a juvenile stage 2. The juvenile stage 2 molts once more until reaching the juvenile 3 stage, which is also called 'filariform'; this is also the infective form. The transformation from rhabditiform to the filariform usually takes five to 10 days. This larval form is able to penetrate human skin, travel through the blood vessels and heart, and reach the lungs. Once there, they burrow through the pulmonary alveoli and travel up the trachea, where they are swallowed and are carried to the small intestine, where they mature into adults and reproduce by attaching themselves to the intestinal wall, causing an increase of blood loss by the host. The eggs end up on the soil after leaving the body through the feces. On average, most adult worms are eliminated in one to two years. The N. americanus life cycle only differs slightly from that of A. duodenale. N. americanus has no development arrest in immune hosts and it must migrate through the lungs.

Epidemiology

N. americanus was first discovered in Brazil and then was found in Texas. Later, it was found to be indigenous in Africa, China, southwest Pacific islands, India, and Southeast Asia. This parasite is a tropical parasite and is the most common species in humans. Roughly 95% of hookworms found in the southern region of the United States are N. americanus. This parasite is found in humans, but can also be found in pigs and dogs.

Transmission of N. americanus infection requires the deposition of egg-containing feces on shady, well-drained soil and is favored by warm, humid (tropical) conditions. Therefore, infections worldwide are usually reported in places where direct contact with contaminated soil occurs.

Symptoms

When adult worms attach to the villi of the small intestine, they suck on the host's blood, which may cause abdominal pain, diarrhea, cramps, and weight loss that can lead to anorexia. Heavy infections can lead to the development of iron deficiency and hypochromic microcytic anemia. This form of anemia in children can give rise to physical and mental retardation. Infection caused by cutaneous larvae migrans, a skin disease in humans, is characterized by skin ruptures and severe itching.

Laboratory diagnosis

The most common technique used to diagnose a hookworm infection is to take a stool sample, fix it in 10% formalin, concentrate it using the formalin-ethyl acetate sedimentation technique, and then create a wet mount of the sediment for viewing under a microscope. However, the eggs of A. duodenale and N. americanus cannot be distinguished; thus, the larvae must be examined to identify these hookworms. Larvae cannot be found in stool specimens unless the specimen was left at ambient temperature for a day or more.

Prevention

Education, improved sanitation, and controlled disposal of human feces are critical for prevention. Nonetheless, wearing shoes in endemic areas helps reduce the prevalence of infection.

Treatment

An infection of N. americanus parasites can be treated by using benzimidazoles, albendazole, and mebendazole. A blood transfusion may be necessary in severe cases of anemia. Light infections are usually left untreated in areas where reinfection is common. Iron supplements and a diet high in protein will speed the recovery process. In a case study involving 56-60 men with Trichuris trichiura and/or N. americanus infections, both albendazole and mebendazole were 90% effective in curing T. trichiura. However, albendazole had a 95% cure rate for N. americanus, while mebendazole only had a 21% cure rate. This suggests albendazole is most effective for treating both T. trichiura and N. americanus.

Cryotherapy by application of liquid nitrogen to the skin has been used to kill cutaneous larvae migrans, but the procedure has a low cure rate and a high incidence of pain and severe skin damage, so it now is passed over in favor of suitable pharmaceuticals. Topical application of some pharmaceuticals has merit, but requires repeated, persistent applications and is less effective than some systemic treatments.

See also

• List of parasites (human)

Notes

References

1. Hotez,P.J.,and D.I.Pritchard.1995(June).Hookworm infection.Sci. Am. 272:68-74.
2. Murray,P.R.,K.S.Rosenthal,and M.A.Pfaller.2009.Medical Mirobiology,6th ed.Elsevier/Mosby Publishing Company,Philadelphia, U.S.A.,865 p.
3. Schmidt,G.D.,and L.S.Roberts.2009.Foundations of parasitology,8th ed.McGraw-Hill Companies,New York,p. 472-473.

UpToDate Contents

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• 1. 鉤虫感染 hookworm infection
• 2. 鉤虫関連皮膚幼虫移行症 hookworm related cutaneous larva migrans
• 3. 集団寄生虫駆除 population deworming
• 4. 肺好酸球増多症の原因 causes of pulmonary eosinophilia
• 5. 駆虫薬療法 anthelminthic therapies

English Journal

• Malaria and helminthic co-infection among HIV-positive pregnant women: prevalence and effects of antiretroviral therapy.

• Ivan E, Crowther NJ, Rucogoza AT, Osuwat LO, Munyazesa E, Mutimura E, Njunwa KJ, Zambezi KJ, Grobusch MP.SourceDepartment of Biomedical Laboratory Sciences, Kigali Health Institute, Rwanda. emil.ivank@gmail.com
• Acta tropica.Acta Trop.2012 Dec;124(3):179-84. doi: 10.1016/j.actatropica.2012.08.004. Epub 2012 Aug 23.
• The impact of malaria on anemia and the interplay with helminths underline the importance of addressing the interactions between HIV/AIDS, malaria and intestinal helminth infections in pregnancy. The aim of this study was to determine the prevalence of malaria-helminth dual infections among HIV posi
• PMID 22940013

• Sequence conservation in the Ancylostoma secreted protein-2 of Necator americanus (Na-ASP-2) from hookworm infected individuals in Thailand.

• Ungcharoensuk C, Putaporntip C, Pattanawong U, Jongwutiwes S.SourceMolecular Biology of Malaria and Opportunistic Parasites Research Unit, Department of Parasitology, Faculty of Medicine, Chulalongkorn University, Bangkok, Thailand.
• Infection, genetics and evolution : journal of molecular epidemiology and evolutionary genetics in infectious diseases.Infect Genet Evol.2012 Dec;12(8):1926-32. doi: 10.1016/j.meegid.2012.08.010. Epub 2012 Sep 1.
• The Ancylostoma secreted protein-2 of Necator americanus (Na-ASP-2) was one of the promising vaccine candidates against the most prevalent human hookworm species as adverse vaccine reaction has compromised further human vaccine trials. To elucidate the gene structure and the extent of sequence diver
• PMID 22964044

Japanese Journal

• A case of mixed infection with Necator americanus and zoonotic Strongyloides sp. acquired in Tanzania

• NOBUSUE K
• Trop Med Hlth 36(1, suppl), 36-37, 2007
• NAID 50006864861

• FDP-E と FDP-Dダイマー値の乖離を認めたアメリカ鉤虫感染症の一例

• 中越 りつこ,小口 弘子,石井 栄三郎,石川 伸介,樋口 由美子,村松 紘一,奥村 伸生,小木曽 嘉文
• 臨床病理 49(1), 82-86, 2001-01-25
• NAID 10007306891

• Hookworm burden reductions in Balb/c mice vaccinated with recombinant Ancylostoma secreted proteins (ASPs) from Ancylostoma duodenale, Ancylostoma caninum and Necator americanus

• LIU S.
• Vaccine 18, 1096-1102, 2000
• NAID 30006365287

Related Links

• Necator americanus - Overview - Encyclopedia of Life

Brief Summary The human hookworms include the nematode species Necator americanus and Ancylostoma duodenale. A larger group of hookworm species normally infecting non-human animals can invade and parasitize humans ...

• ADW: Necator americanus: INFORMATION

Read about Necator americanus on the Animal Diversity Web. ... tropical savanna and grassland A terrestrial biome. Savannas are grasslands with scattered individual trees that do not form a closed canopy. Extensive savannas are ...

Related Pictures

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★リンクテーブル★

リンク元	「蠕虫」「N. americanus」
関連記事	「Necator」

「蠕虫」

　　[★]

英

helminth, worms

ラ

helminthen

関

微生物学、蠕虫症、家畜伝染病予防法

蠕虫類

• 吸虫類 trematoda
• 条虫類 cestoda
• 線虫類 nematoda
• 鉤頭虫類 acanthocephala

蠕虫類と感染症

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
	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)

「N. americanus」

　　[★]

• アメリカ鉤虫

関

Necator、Necator americanus

「Necator」

　　[★]

アメリカ鉤虫、メリカ鉤虫属、ネカトール属、Necator属

関

N. americanus、Necator americanus