In epidemiological research work, the Oswaldo Cruz Institute (IOC/Fiocruz) confirmed the presence of the worm Angiostrongylus cantonensis, causing eosinophilic meningitis, in snails collected in the city of Nova Iguaçu, Baixada Fluminense, in the Rio de Janeiro state. Identification was carried out by the Malacology Laboratory of IOC, which acts as the National Reference Laboratory for Schistosomiasis-Malacology. 

Microscopy image of worms Angiostrongylus cantonensis detected in snails (photo: Josué Damacena/IOC/Fiocruz)

The Reference Service was activated by the Municipal Health Department of Nova Iguaçu after a death from the disease was confirmed in the city, on April 22. Professionals from the municipality's Environmental Health Surveillance Superintendence (Suvam/Nova Iguaçu) and the Malacology Laboratory of the IOC carried out snail collections at different points in the Ipiranga neighborhood, belonging to the Cabuçu Regional Government Unit (URG Cabuçu), where the patient contracted the infection. 

The worm that causes the disease was detected in an aquatic snail of the genus Pomacea, popularly known as lolô or aruá. Detection was carried out through a parasitological examination of the mollusks and genetic sequencing of the parasite. A total of 22 mollusks were analyzed. And one of the species Pomacea maculata was infected. The finding was communicated by the Reference Service to the local Health Department and the Ministry of Health. 

After confirming the infection in the mollusk, another team from the IOC became part of epidemiological research in the city. The Laboratory of Biology and Parasitology of Wild Mammals Reservoirs, which acts as a Brazilian National Reference in Taxonomy and Diagnosis of Wild Leishmaniasis Reservoirs, was contacted by the Superintendency of Environmental Health Surveillance of Nova Iguaçu. Specialists from the Reference Service began field investigation in the Ipiranga neighborhood to identify animals that act as reservoirs for the worm cantonensis in the locality. The activity was in collaboration with the Clinical Research Laboratory on Dermatozoonosis in Domestic Animals of the Evandro Chagas National Institute of Infectious Diseases (INI/Fiocruz) and support from Suvam/Nova Iguaçu. In total, 15 animals were collected, including rats, opossums and cavies. Analyzes are underway to confirm infection in mammals. 

Disease cycle 

Meningitis transmitted by snails is called eosinophilic meningitis. The disease is caused by the worm Angiostrongylus cantonensis. In the life cycle of this worm, rodents (for example, urban rats) act as hosts for the adult forms of the parasite, which reproduce in the animals' bodies and generate larvae (young forms of the worm). The larvae are eliminated in rat feces and ingested by snails. Inside mollusks, they acquire the form capable of infecting vertebrate animals. Human infection occurs when people ingest an infected snail or the mucus it releases, containing the worm larvae. 

Snails of the genus Pomacea were analyzed at the Malacology Laboratory of IOC (photo: Joshua Damacena/IOC/Fiocruz)

The head of the Malacology Laboratory at the IOC, Silvana Thiengo, warns of the importance of raising awareness about the disease, which can be transmitted by different species of snails. “In Brazil, many cases are associated with the mollusk Achatina fulica, known as the giant African snail. However, other terrestrial and aquatic mollusks can also transmit the parasite. The population needs to be alert to take care when handling snails, clean vegetables and not eat these animals raw or undercooked," said the researcher. 

The responsible for the Suvam/Nova Iguaçu Malacological Surveillance sector, José de Arimatea Brandão Lourenço, says that the guidelines for the population have been reinforced in the region where the case was registered. “Reports indicate that the patient became infected after ingesting a raw freshwater snail. We carried out actions to reinforce information to alert the population in the area to avoid new cases", said Arimatea. 

Symptoms, treatment and prevention 

Headache is the most common symptom of the disease. Neck stiffness and fever, which are common in other forms of meningitis, occur in only some cases of eosinophilic meningitis. Some patients also experience visual disturbances, nausea, vomiting and persistent paresthesia (such as, for example, a tingling sensation or numbness). In most cases, the patient heals spontaneously. However, medical monitoring is important because some individuals develop serious conditions, which can lead to death. Treatment seeks to reduce inflammation in the central nervous system and alleviate pain, in addition to preventing complications. 

Because of its large reproduction and wide distribution in the country, the giant African snail plays an important role in the spread of eosinophilic meningitis. To combat this vector, it is recommended to manually collect the snails, as follows: 

• Collect the snails using gloves or plastic bags to protect your hands; 

• Place them in a container of boiling water for five minutes; 

• Break the shells and bury them or throw them in the trash (shells should not be discarded whole because they can accumulate water, becoming breeding grounds for the Aedes aegypti mosquito). 

Other important precautions are: 

• Do not eat raw or undercooked shellfish, including land snails, slugs and aquatic snails; 

• Wash fruits and vegetables well, leaving them to soak for 30 minutes in a mixture with a liter of water and a tablespoon of bleach, rinsing them well in running water before consumption. 

Presence of the parasite in RJ 

Research led by the Malacology Laboratory of the IOC demonstrates the circulation of the worm cantonensis in Rio de Janeiro. In the capital, a survey detected the worm cantonensis in 6% of the snails collected in the Pedra Branca State Park, in Jacarepaguá. 

The survey was part of the dissertation by Flavia Cristina dos Santos Rangel, carried out at the Postgraduate Program in Health Biodiversity do IOC. [Check out the article.] The case registered in Nova Iguaçu was the third human infection confirmed in the state. The other two cases were registered in a 2014 Study, which mapped the spread of eosinophilic meningitis in the country. For the head of the Malacology Laboratory at IOC, the scenario reinforces the need for attention from health services to diagnose the condition.  

“Since 2006, we have had cases of eosinophilic meningitis in Brazil. However, many healthcare professionals are still unaware of the disease. Doctors need to remember this possibility to make the diagnosis and offer appropriate treatment", highlighted Silvana. 

Focus on surveillance 

The importance of vigilance is also emphasized. To map the risk of infection, municipalities must periodically collect mollusks of medical interest and send the specimens for parasitological analysis, which is carried out by the Reference Service of the IOC.  To strengthen this activity, the Malacology Laboratory of the IOC offers training in medical malacology for the municipalities of Rio de Janeiro, in partnership with the State Department of Health (SES/RJ). However, the coordinator of the National Reference Laboratory for Schistosomiasis-Malacology of the IOC, Elizangela Feitosa, notes that monitoring is still incipient in most of the state. 

“There are few municipalities that send specimens for parasitological analysis regularly. Vector surveillance services often need to focus their teams on combating epidemic diseases, such as dengue, and snail surveillance is left unguarded”, states the researcher. 

African giant snail is approximately 7 to 12 cm long in adulthood and can lay up to 400 eggs per clutch (photo: Josué Damacena/IOC/Fiocruz)

Nova Iguaçu is one of the cities where monitoring is carried out regularly. The person responsible for Malacological Surveillance in the city highlights that the work mapped snails infected by the eosinophilic meningitis worm in all regions of the city. 

“Generally, the population appeals because of the nuisance caused by the African snail. But, knowing that we have an emerging disease, we collected samples for parasitological surveillance and showed residents how to collect snails safely, to try to reduce or eliminate this vector”, details Arimatea, who has a master's degree in the IOC's Postgraduate Program in Vector Surveillance and Control. 

The experts emphasize that the warning also applies to other states in Brazil. From 2008 to 2021, the Reference Service for Schistosomiasis-Malacology detected the worm cantonensis in mollusks from 14 federation units. [Check out the article.] 

“We hope that this alert can encourage other states to maintain malacological surveillance. It is important that the Health Departments and the medical profession are aware of this scenario for effective prevention and faster diagnoses”, highlights the biologist at the Malacology Laboratory Jucicleide Souza.