Angiostrongylus cantonensis: Agent of a Sometimes Fatal Globally Emerging Infectious Disease (Rat Lungworm Disease) Robert H. Cowie* Pacific Biosciences Research Center, University of Hawaii, Honolulu, Hawaii 96822, United States ABSTRACT: Angiostrongylus cantonensis, the rat lungworm, is a dangerous invasive species that is the agent of a potentially fatal globally emerging infectious disease. Humans are infected most commonly by ingestion, deliberately or inadvertently, of the parasite larvae in their intermediate snail hosts. The larvae make their way to the brain where they can cause severe neurological damage before eventually dying. Symptoms of the disease are diverse, making it difficult to diagnose. Treatment is primarily with corticosteroids to reduce inflammation, while treatment with anthelmintics to kill the worms remains controversial. There have been almost 3000 cases globally, the majority in southern China, but the parasite is spreading and now occurs much more widely. In the USA, almost all cases have been in Hawaii, but the parasite is also present in southeastern states. As the climate warms, this tropical/subtropical parasite is likely to spread further. KEYWORDS: Albendazole, Angiostrongylus cantonensis, eosinophilic meningitis, nematode, parasite, prednisolone, rat lungworm T he rat lungworm, Angiostrongylus cantonensis, is a nematode, the definitive and intermediate hosts of which are rats and snails/slugs (snails from here on), respectively. 1 Adult worms reproduce in the rat’s pulmonary arteries. Eggs hatch into first stage larvae in the lungs. The larvae then move up the trachea, and are swallowed and released in the feces. Snails feed on those feces, ingesting the worms, which develop in the snails through the second to the third, infective, larval stage. The natural cycle continues when a rat eats the infected snail. The larvae penetrate the intestinal wall, entering the circulatory system, and thence the central nervous system and ultimately the brain. In the brain they develop through the fourth stage to the subadult stage and then return via the circulatory system to the pulmonary arteries, where they become mature, mate, and lay eggs. Human infection, as accidental hosts, is by ingestion of third stage larval worms, most commonly by eating an infected raw snail, deliberately (as a delicacy, for instance in southern China, or even on a dare) or inadvertently (most commonly on contaminated produce). 1,2 The worms reach the brain, just as in the rat, develop to the subadult stage, but then die rather than returning to the circulatory system and reproducing. The damage caused by the worms as they move around in the brain, combined with an immune reaction that seems particularly intense in response to the dying worms, causes neurological damage that can be severe and permanent. Infection generally manifests as eosinophilic meningitis, although this can be caused by other agents. 3 The disease is commonly known as rat lungworm disease or angiostrongyliasis. However, the latter term is also applied to infection with Angiostrongylus costaric- ensis, which causes a gastrointestinal syndrome. Various other terms have therefore been coined to permit distinguishing the two syndromes, including neuroangiostrongyliasis and, because of the characteristic heightened level of eosinophils in the cerebrospinal fluid, angiostrongylus eosinophilic meningitis. 3 Symptoms of the disease are diverse. 3 A mild infection may result in headache, neck and shoulder pain, sensitivity and tingling of the skin, visual disturbance, various other symptoms, and perhaps some fever, all of which may resolve sponta- neously, even without the person realizing they were infected. In more severe cases, these symptoms may be much more intense and additional symptoms such as motor disturbance and digestive and urinary tract malfunction may occur. Extremely severe cases may lead to coma and occasionally death. The diverse array of symptoms is presumably related to the location of the worms and of the neurological damage they cause in different parts of the brain. As such, diagnosis is difficult and relies not only on clinical symptoms but also on food consumption history involving potential exposure to the parasite (via intermediate and paratenic hosts 2 ), residence in or history of visiting areas where the parasite is present, supportive but not necessarily diagnostic CT and MRI scans, finding of eosinophils in the cerebrospinal fluid, and serological tests that as yet are not consistently reliable. 3 Treatment protocols are not definitive. 3 Analgesics can be used for pain. Spinal taps may decrease intracranial pressure and relieve headaches, at least temporarily, as well as decrease the likelihood of neurological damage. Corticosteroids (e.g., prednisolone) are generally used, sometimes in conjunction with spinal taps, and are postulated to provide relief by reducing inflammation and thereby intracranial pressure. 3 At first sight, use of anthelmintics (benzimidazoles, most notably albendazole) to kill the worms would seem appropriate. However, this remains controversial. 3 Since the immune reaction to dying worms seems greater than to the live worms, killing all at the same time may be worse than allowing them to die naturally. Nonetheless, anthelmintics may be effective in reducing severity and duration of headaches, although definitive evidence is limited. 3 Furthermore, there is evidence, again limited, that a combination of steroids and anthelmintics may reduce severity and duration of illness, 3 Received: September 1, 2017 Accepted: September 5, 2017 Published: September 13, 2017 Viewpoint pubs.acs.org/chemneuro © 2017 American Chemical Society 2102 DOI: 10.1021/acschemneuro.7b00335 ACS Chem. Neurosci. 2017, 8, 2102-2104 Cite This: ACS Chem. Neurosci. 2017, 8, 2102-2104 Downloaded via 14.185.88.171 on July 14, 2023 at 04:27:11 (UTC). See https://pubs.acs.org/sharingguidelines for options on how to legitimately share published articles.
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