Angiostrongyliasis (Rat Lungworm)
Angiostrongyliasis, also known as rat lungworm, is a disease that affects the brain and spinal cord. It is caused by a parasitic nematode (roundworm parasite) called Angiostrongylus cantonensis. The adult form of A. cantonensis is only found in rodents. However, infected rodents can pass larvae of the worm in their feces. Snails, slugs, and certain other animals (including freshwater shrimp, land crabs, and frogs) can become infected by ingesting this larvae; these are considered intermediate hosts. Humans can become infected with A. cantonensis if they eat (intentionally or otherwise) a raw or undercooked infected intermediate host, thereby ingesting the parasite. For more information on the life-cycle of A. cantonensis, visit the CDC website.
This infection can cause a rare type of meningitis (eosinophilic meningitis). Some infected people don’t have any symptoms or only have mild symptoms; in some other infected people the symptoms can be much more severe. When symptoms are present, they can include severe headache and stiffness of the neck, tingling or painful feelings in the skin or extremities, low-grade fever, nausea, and vomiting. Sometimes, a temporary paralysis of the face may also be present, as well as light sensitivity. The symptoms usually start 1 to 3 weeks after exposure to the parasite, but have been known to range anywhere from 1 day to as long as 6 weeks after exposure. Although it varies from case to case, the symptoms usually last between 2–8 weeks; symptoms have been reported to last for longer periods of time.
You can get angiostrongyliasis by eating food contaminated by the larval stage of A. cantonensis worms. In Hawaii, these larval worms can be found in raw or undercooked snails or slugs. Sometimes people can become infected by eating raw produce that contains a small infected snail or slug, or part of one. It is not known for certain whether the slime left by infected snails and slugs are able to cause infection. Angiostrongyliasis is not spread person-to-person.
Diagnosing angiostrongyliasis can be difficult, as there are no readily available blood tests. In Hawaii, cases can be diagnosed with a polymerase chain reaction (PCR) test, performed by the State Laboratories Division, that detects A. cantonensis DNA in patients’ cerebrospinal fluid (CSF) or other tissue. However, more frequently diagnosis is based on a patient’s exposure history (such as if they have history of travel to areas where the parasite is known to be found or history of ingestion of raw or undercooked snails, slugs, or other animals known to carry the parasite) and their clinical signs and symptoms consistent with angiostrongyliasis as well as laboratory finding of eosinophils (a special type of white blood cell) in their CSF. There is no reliable diagnostic test available to detect previous infections of angiostrongyliasis.
There is no specific treatment for the disease. The parasites cannot mature or reproduce in humans and will die eventually. Supportive treatment and pain medications can be given to relieve the symptoms, and some patients are treated with steroids. No anti-parasitic drugs have been shown to be effective in treating angiostrongyliasis, and there is concern that they could actually make the symptoms worse because of the body’s response to potentially more rapidly dying worms. Persons with symptoms should consult their health care provider for more information.
Being infected with angiostrongyliasis does not protect you against becoming infected again in the future from another exposure to A. cantonensis.
To prevent angiostrongyliasis, don’t eat raw or undercooked snails or slugs, and if you handle snails or slugs, be sure to wear gloves and wash your hands. Eating raw or undercooked freshwater shrimp, land crabs and frogs may also result in infection, although, there has not been any documented cases in Hawaii. You should also thoroughly inspect and rinse produce, especially leafy greens, in potable water, and boil snails, freshwater prawns, crabs, and frogs for at least 3–5 minutes. Eliminating snails, slugs, and rats founds near houses and gardens might also help reduce risk exposure to A. cantonensis.
Qvarnstrom Y, Xayavong M, da Silva ACA, et al. 2015. Real-Time Polymerase Chain Reaction Detection of Angiostrongylus cantonensis DNA in Cerebrospinal Fluid from Patients with Eosinophilic Meningitis. Am J Trop Med Hyg. (Epub ahead of print) View article
Kwon E, Ferguson TM, Park SY, et al. 2013. A Severe Case of Angiostrongylus Eosinophilic Meningitis with Encephalitis and Neurologi Sequelae in Hawaii. Hawaii J Med Public Health. 72(6): 41–5 View article
Wilkins PP, Qvarnstrom Y, Whelen AC, et al. 2013. The Current Status of Laboratory Diagnosis of Angiostrongylus cantonensis Infections in Humans Using Serologic and Molecular Methods. Hawaii J Med Public Health. 72(6): 55–7 View article
Hochberg NS, Blackburn BG, Park SY, et al, 2011. Eosinophilic Meningitis Attributable to Angiostrongylus cantonensis Infection in Hawaii: Clinical Characteristics and Potential Exposures. Am J Trop Med Hyg. 85(4): 685–90 View article
Hochberg NS, Park SY, Blackburn BG, et al, 2007. Distribution of Eosinophilic Meningitis Cases Attributable to Angiostrongylus cantonensis, Hawaii. Emerg Infect Dis. 13(11): 1675–80 View article
Hollingsworth RG, Kaneta R, Sullivan JJ, et al. 2007. Distribution of Parmarion cf. martensi (Pulmonata: Helicarionidae), a New Semi-Slug Pest on Hawai‘i Island, and Its Potential as a Vector for Human Angiostrongyliasis. Pac Sci. 61(4): 457–67
Qvarnstrom Y, Sullivan JJ, Bishop HS, Hollingsworth R, da Silva AJ. 2007. PCR-Based Detection of Angiostrongylus cantonensis in Tissue and Mucus Secretions from Molluscan Hosts. Appl Environ Microbiol. 73(5): 1415–1419 View article
Angiostrongyliasis should be considered in a patient with headache, nuchal rigidity, and a consistent exposure history. Patients may also have other neurological manifestations such as sensory nerve abnormalities, paresthesias, paresis, or other deficits depending on where larvae have migrated in the brain.
A diagnosis of angiostrongyliasis infection is strongly suggested when the following are present:
- The patient’s symptoms are suggestive of bacterial meningitis, but testing reveals eosinophilia either in the blood (>5%) or especially in cerebrospinal fluid (>10%).
- The patient has a history of ingestion of raw or undercooked intermediate hosts (e.g., snails, slugs, and certain other animals such as freshwater shrimp, land crabs, and frogs)
- Examination of the patient’s CSF reveals eosinophilia (>10% eosinophils), elevated protein, and low or normal glucose. (It should be noted that eosinophilia in the CSF and in the blood may not be present on initial presentation or in late stages of infection)
- Generally, CSF opening pressure is elevated.
Tests for angiostrongyliasis:
- Recovery of A. cantonensis from the patient’s CSF confirms the diagnosis; however, the organism is rarely detected on microscopy as it can adhere to the meninges and often migrates in neural tissue rather than remaining in the extrameningeal space.
- Serologic tests have been developed but are not commercially available. A few specialty or research laboratories offer serologic tests, but the sensitivity and specificity of the tests have not been found to offer reliable results, with such results varying from laboratory to laboratory; additionally, the infection is often identified only on convalescent sera.
- Some research laboratories have developed PCR tests for use with CSF and tissue. In Hawaii, patient specimens can be forwarded to the State Laboratories Division (SLD) for PCR testing (pending reporting to HDOH – see below) developed by the Centers for Disease Control and Prevention (CDC). Clinicians with a patient in whom they suspect angiostrongyliasis should report such cases to HDOH to facilitate testing and public health investigation. Only specimens collected during the acute phase of infection are able to be tested by PCR.
- Neuroimaging studies are often nonfocal without any characteristic lesions. Despite this, they may be helpful to distinguish A. cantonensis eosinophilic meningitis from focal lesions which is more commonly seen with other parasitic infections such as neurocysticercosis and gnathostomiasis.
Because eggs are not passed in the feces, a stool examination is not useful for diagnosis.
The treatment of angiostrongyliasis is generally supportive with analgesics for pain and corticosteroids to limit the inflammatory reaction. Therapeutic lumbar punctures, repeated as clinically indicated, may help relieve headache, which can be debilitating and unremitting, in patients with elevated intracranial pressure. No anti-helminthic drugs have been proven to be effective in treatment; there has been concern that anti-helminthics could exacerbate neurological symptoms due to the inflammatory response to the dying worms. Additional symptomatic treatment may also be required for nausea, vomiting, and in some cases, chronic pain due to nerve damage and muscle atrophy.
HDOH requires that clinicians report patients with eosinophilic meningitis, i.e., signs and/or symptoms consistent with meningitis plus eosinophils in the cerebrospinal fluid (CSF) without possible alternative causes, including CNS infection with other microbes, reaction to foreign material in the CNS (e.g., intracranial hardware or myelography dye), medications (e.g., intrathecal vancomycin or gentamicin), neoplasms, multiple sclerosis, and neurosarcoidosis by calling (808) 586-4586.
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