Chapter 3Infectious Diseases Related To Travel

Barbara L. Herwaldt

INFECTIOUS AGENT

Angiostrongyliasis is caused by Angiostrongylus cantonensis, a nematode parasite that is considered the most common infectious cause of eosinophilic meningitis in humans.

MODE OF TRANSMISSION

Various species of rats are the definitive hosts of the parasite, also known as the rat lungworm. The mature (adult) form of the parasite is found only in rats, not in humans or other hosts. Infected rats shed first-stage larvae, which are infective for snails and slugs but not for humans or for transport hosts (defined below), in their feces.

Snails and slugs are intermediate hosts. They become infected by ingesting first-stage larvae in rat feces. These immature larvae mature to third-stage larvae, which are infective for rats (in which they develop to adult worms), other animals, and humans. Humans become infected by eating snails or slugs, whether for cultural reasons, “on a dare,” or accidentally, such as by ingesting contaminated raw produce, including lettuce and vegetable juices.

Infective larvae have been found in various transport (paratenic) hosts, such as freshwater shrimp or prawns, crabs, and frogs (fish are not known to transmit the parasite). The parasite does not mature in paratenic hosts, but they can transport infective larvae. Some transport hosts (for example, raw frogs) have been associated with human infection; however, the importance of transport hosts in transmitting the parasite is unclear.

EPIDEMIOLOGY

Most of the described cases have occurred in Asia and the Pacific Basin (such as in parts of Thailand, Taiwan, mainland China, the Hawaiian Islands, and other Pacific Islands). However, cases have been reported in many areas of the world, including the Caribbean. The geographic range of the parasite is expanding, probably facilitated by infected shipborne rats and the diversity of snail species that can be intermediate hosts.

Both individual and outbreak-associated cases have been described. An outbreak of A. cantonensis–associated eosinophilic meningitis occurred among a group of US travelers exposed in Jamaica in 2000, before angiostrongyliasis was known to be endemic there. The presumptive vehicle was the lettuce in a salad.

CLINICAL PRESENTATION

Ingested larvae can migrate to the central nervous system and cause eosinophilic meningitis. Typically, the incubation period is about 1–3 weeks but has ranged from approximately 1 day to >6 weeks. Common manifestations include headache, photophobia, stiff neck, nausea, vomiting, fatigue, and body aches. Abnormal skin sensations (such as tingling or painful feelings) are more common than in other types of meningitis. A low-grade fever might be noted. The symptoms and signs may persist for weeks or months but are usually self-limited. Severe cases can be associated with sequelae such as paralysis or blindness or death.

DIAGNOSIS

Typically, the diagnosis is presumptive, on the basis of clinical and epidemiologic criteria, in people with otherwise unexplained eosinophilic meningitis. If lumbar punctures are done early or late in the course of infection, few, if any, eosinophils may be found in the cerebrospinal fluid. Peripheral blood eosinophilia is occasionally noted. Parasitologic confirmation of the diagnosis—by detecting A. cantonensis larvae in the cerebrospinal fluid—is unusual in most settings. Serologic assays and other diagnostic modalities are considered investigational but might provide supportive evidence for the diagnosis.

TREATMENT

The larvae die spontaneously, and supportive care usually suffices. The use of corticosteroid or antiparasitic therapy should be individualized, with expert consultation. The utility of such therapy may differ among A. cantonensis–endemic areas. Clinicians may consult with CDC about evaluation and treatment of patients (404-718-4745; parasites@cdc.gov). Additional information can be found at www.cdc.gov/parasites/angiostrongylus.

PREVENTIVE MEASURES FOR TRAVELERS

No vaccine is available. Preventive measures are aimed at reducing the risk of ingesting the parasite. In particular, travelers are advised to follow standard food and water precautions (see Chapter 2, Food and Water Precautions) and particularly to:

• Avoid eating raw or undercooked snails, slugs, and other possible hosts.
• Eat raw produce, such as lettuce, only if it has been thoroughly washed or treated with bleach.
• Wear gloves (and wash hands) if snails or slugs are handled.

BIBLIOGRAPHY

1. Hochberg NS, Park SY, Blackburn BG, Sejvar JJ, Gaynor K, Chung H, et al. Distribution of eosinophilic meningitis cases attributable to Angiostrongylus cantonensis, Hawaii. Emerg Infect Dis. 2007 Nov;13(11):1675–80.
2. Lai CH, Yen CM, Chin C, Chung HC, Kuo HC, Lin HH. Eosinophilic meningitis caused by Angiostrongylus cantonensis after ingestion of raw frogs. Am J Trop Med Hyg. 2007 Feb;76(2):399–402.
3. Slom TJ, Cortese MM, Gerber SI, Jones RC, Holtz TH, Lopez AS, et al. An outbreak of eosinophilic meningitis caused by Angiostrongylus cantonensis in travelers returning from the Caribbean. N Engl J Med. 2002 Feb 28;346(9):668–75.
4. Tsai HC, Lee SS, Huang CK, Yen CM, Chen ER, Liu YC. Outbreak of eosinophilic meningitis associated with drinking raw vegetable juice in southern Taiwan. Am J Trop Med Hyg. 2004 Aug;71(2):222–6.
5. Wang QP, Lai DH, Zhu XQ, Chen XG, Lun ZR. Human angiostrongyliasis. Lancet Infect Dis. 2008 Oct;8(10):621–30.