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Angiostrongyliasis or rat lungworm disease is a type of disease that affects the spinal cord and the brain in human beings. Angiostrongylus cantonensis, a parasitic nematode found in rodents, is the root cause of this disease. Snails, slugs, as well as other animals serve as mediators of this parasite and when humans consume such animals, or food and water contaminated by the larvae of the rat lungworm, they get affected by the disease.
These parasites were first identified in China in 1935. Since the discovery of A. catanonensis in 1944 as the cause of Eosinophilic Meningitis in Taiwan, much research has been done to study the parasite and disease caused. The nematode was first found in a patient affected with Eosinophilic Meningitis.
It was in 1955 that the first study on the topic was published. This research done by Mackerass and Sanders determined the life cycle of the parasite in rats. They marked snails and slugs as the intermediate hosts. They also noted that the transmission path of the rat lungworm is through the blood, brain, and lungs of rats.
The Hawaii islands are a part of the United States of America. This island is considered as the most affected area by rat lungworm disease. In 1961, three researchers, namely, Rosen, Laigret, and Bories conducted a study to know whether fish carried the parasite that caused eosinophilic meningitis in humans. This study sampled the people in the Hawaii islands, where people infected with the parasite were found to be very common. Raw fish was consumed by a large number of people in the sample population. But it was found that patients who showed symptoms of meningitis had a history of having raw snails or prawns within two weeks before presenting with the symptoms. Thus, when this study is combined with the epidemiology and autopsy of the patients’ brains, it proves that A. cantonensis is transmitted by snails and not fish.
In 1965, Joseph E. Alicata conducted a study on “Biology and Distribution of the Rat Lungworm, Angiostrongylus cantonensis, and its Relationship to Eosinophilic Meningoencephalitis and other Neurological Disorders of Man and Animals.” The study described the ability of the nematode in migration, development, and production of eosinophilic meningoencephalitis in man and other hosts.
In June 2013, a study named “A Severe Case of Rat Lungworm Disease in Hawaii” was published by Kathleen Howe. It was a case study of a 23-year-old man from the Hawaii islands, who was suffering from eosinophilic meningitis. This study described how he recovered from the initial comatose stage and how he slowly came out of the disease taking 4 long years.
In July 2015, further research by the University of Hawaii revealed that the Puna district on the Island of Hawaii is the epicenter of rat lungworm disease in the U.S.; this research was undertaken by Susan Jarvi, a professor from the University.
Jarvi and her research team studied the possibility of DNA detection of the parasite in rat blood, so that it could help in early diagnosis of the disease in humans.
The history of rat lungworm was studied by two researchers, M.J. Mackerras and D.F. Sandars of Australia, in 1955. Their research explains the life cycle and development of the parasite from rats to humans. Stage-by-stage the research clearly marks the entire journey of the parasite with the exact number of days needed in each stage.
A study of eosinophilic meningitis was conducted over a period of 3 years in Thailand that ended in March 1968. A total of 640 patients with eosinophilic pleocytosis were considered as samples and 484 cases of eosinophilic meningitis were found among them. The symptoms at various stages of the disease were studied and it was found that steroids and antibiotics did not have much effect on the illness.
In 2006–07, China conducted the first national survey on Angiostrongylus cantonensisinvolving 160 patients. The research conducted by 10 researchers was published in February 2009. The study found that two snails were responsible for carrying the rat lungworm—A. fulica and P. canaliculata. These snails were responsible for the outbreak of angiostrongyliasis in the mainland of China, which was previously a rare disease.
“Angiostrongylus cantonensis and Rat Lungworm Disease in Brazil” was a study by a group of scholars during 2013. Since 2007, seven cases were reported in Brazil showing infection by the parasite. The study found the presence of two infected specimens of Rattus norvegicus and Rattus rattus as well as many species of mollusks, including the giant African land snail from various regions of Brazil.
The study proposes many suggestions for the control and monitoring of hosts (both intermediate and definitive). It emphasizes the need for creating awareness to the public on disease transmission and prevention.
Reviewed by Afsaneh Khetrapal BSc (Hons)