Angiostrongyliasis
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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1]
Overview
Historical Perspective
Classification
Pathophysiology
Causes
Differentiating Angiostrongyliasis From Other Diseases
Epidemiology and Demographics
Risk Factors
Natural History, Complications and Prognosis
Diagnosis
History and Symptoms | Physical Examination | Laboratory Findings | Other Imaging Findings | Other Diagnostic Studies
Treatment
Medical Therapy | Surgery | Primary Prevention | Secondary Prevention | Future or Investigational Therapies
Case Studies
Related Chapters
Transmission
Transmission of the parasite is usually from eating raw or undercooked snails or other vectors. Infection is also frequent from ingestion of contaminated water or unwashed salad that may contain small snail and slugs, or have been contaminated by them. Therefore it is very important to avoid raw snails, wash and cook vegetables thoroughly, and avoid open water sources that may be contaminated.
Reservoirs
Rats are the definitive host and the main reservoir for A. cantonensis, though other small mammals may also become infected. While angiostrongylus can infect humans, humans do not act as reservoirs since the worm cannot reproduce in humans and therefore humans cannot contribute to their life cycle.[1]
Vectors
A. cantonensis has many vectors, with the most common being several species of snails, including the giant African land snail (Achatina fulica) in the Pacific islands and snails of the genus Pila in Thailand and Malaysia. The golden apple snail, A. canaliculatus, is the most important vector in areas of China.[2] Freshwater prawns, crabs, or other paratenic, or transport, hosts can also act as vectors.[1]
Incubation period
The incubation period in humans is usually from 1 week to 1 month after infection, and can be as long as 47 days.[3] This interval varies, since humans are intermediate hosts and, the life cycle does not continue predictably as it would in a rat.[1]
Morphology
A. cantonensis is a nematode roundworm with 3 outer protective collagen layers, and a simple stomal opening or mouth with no lips or buccal cavity leading to a fully developed gastrointestinal tract.[4] Males have a small copulatory bursa at the posterior. Females have a “barber pole” shape down the middle of the body, which is created by the twisting together of the intestine and uterine tubules. The worms are long and slender - males are 15.9-19 mm in length, and females are 21-25 mm in length.[5]
Life cycle
The adult form of A. cantonensis resides in the pulmonary arteries of rodents, where it reproduces. After the eggs hatch in the arteries, larvae migrate up the pharynx and are then swallowed again by the rodent and passed in the stool. These first stage larvae then penetrate or are swallowed by snail intermediate hosts, where they transform into second stage larvae and then into third stage infective larvae. Humans and rats acquire the infection when they ingest contaminated snails or paratenic (transport) hosts including prawns, crabs, and frogs, or raw vegetables containing material from these intermediate and paratenic hosts. After passing through the gastrointestinal tract, the worms enter circulation.[3] In rats, the larvae then migrate to the meninges and develop for about a month before migrating to the pulmonary arteries, where they fully develop into adults.[1]
Humans are incidental hosts; the larvae cannot reproduce in humans and therefore humans do not contribute to the A. cantonensis life cycle. In humans, the circulating larvae migrate to the meninges, but do not move on to the lungs. Sometimes the larvae will develop into the adult form in the brain and CSF, but they quickly die, inciting the inflammatory reaction that causes symptoms of infection.[1]
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Angiostrongyliasis Life Cycle
Adapted from CDC
Epidemiology
A. cantonensis and its vectors are endemic to Southeast Asia and the Pacific Basin.[4] The infection is becoming increasingly important as globalization allows it to spread to more and more locations, and as more travelers encounter the parasites. The parasites probably travel effectively through rats traveling as stowaways on ships, and through the introduction of snail vectors outside endemic areas.
Although mostly found in Asia and the Pacific where asymptomatic infection can be as high as 88%, human cases have been reported in the Caribbean, where as much as 25% of the population may be infected. In the US, cases have been reported Hawaii, which is in the endemic area [5]. The infection is now endemic in wildlife and a few human cases have also been reported in areas where the parasite was not originally endemic, such as New Orleans and Egypt.
Public health and prevention
There are many public health strategies that can drastically limit the transmission of A. cantonensis by limiting contact with infected vectors. Vector control may be possible, but has not been very successful in the past. Education to prevent the introduction of rats or snail vectors outside endemic areas is important to limit the spread of the disease.[6] There are no vaccines in development for angiostrongyliasis.
Recommendations for individuals
To avoid infection when in endemic areas, travelers should:
- Avoid consumption of uncooked vectors, such as snails and freshwater prawns
- Avoid drinking water from open sources, which may have been contaminated by vectors
- Prevent young children from playing with or eating live snails
- ↑ 1.0 1.1 1.2 1.3 1.4 Invalid
<ref>tag; no text was provided for refs namedDavid2006 - ↑ Invalid
<ref>tag; no text was provided for refs namedHuaLi2008 - ↑ 3.0 3.1 Invalid
<ref>tag; no text was provided for refs namedRamirez-Avila2009 - ↑ 4.0 4.1 Invalid
<ref>tag; no text was provided for refs namedBaheti2008 - ↑ http://animaldiversity.ummz.umich.edu/site/accounts/information/Angiostrongylus_cantonensis.html, Accessed 2/26/09
- ↑ JE Alicata (1991). “The Discovery of Angiostrongylus Cantonensis as a Cause of Human Eosiniphilc Meningitis”. Parasitology Today, 7(6): 151-153.