The CDC found a parasite called Angiostrongylus cantonensis (A. cantonensis) in brown rats from Atlanta. Humans can get infected by consuming snails or other foods that have picked up rat droppings.
A. cantonensis infections can cause angiostrongyliasis and eosinophilic meningoencephalitis, a type of meningitis marked by significant eosinophils in the cerebrospinal fluid.
A. cantonensis infections are very rare but must be considered when diagnosing eosinophilic meningitis
A new study conducted by the Centers for Disease Control and Prevention (CDC) found a parasite called Angiostrongylus cantonensis (A. cantonensis or rat lungworm) in brown rats from Atlanta.
To determine the prevalence of A. cantonensis in brown rats, the CDC collected tissue samples from 33 wild brown rats found dead in Atlanta between 2019 and 2022. To assess the presence of the parasite, they examined tissue from the rats’ brain, heart, liver, kidney, lung, spleen, skeletal muscle, skin, gastrointestinal tract, adrenal gland, and gonads.
“We stored samples in 10% neutral buffered formalin and processed them for routine histopathologic evaluation as part of opportunistic monitoring of wildlife found dead on zoo grounds,” the CDC notes. They found that seven samples showed the presence of nematodes (roundworms). Of those seven, four tested positive for A. cantonensis through histologic examination of the heart, pulmonary artery, and brain tissues.
“Although we molecularly confirmed diagnosis in only 4/7 cases, the remaining rats had intravascular nematodes morphologically consistent with A. cantonensis and typical associated lesions,” the CDC notes. “We could not molecularly confirm the remaining 3 cases because of insufficient sample quality and DNA degradation; thus, we could not rule out the presence of other nematode species.”
Brian Labus, PhD, MPH, REHS, an assistant professor in the Department of Epidemiology and Biostatistics at the University of Nevada Las Vegas, explains what the parasite is and how it eventually enters the human body: “Angiostrongylus cantonensis is a parasitic worm that is normally found in rats, which mollusks like snails or slugs can pick up from rat droppings. People get infected with it by consuming raw or undercooked snails or pieces of snails that are accidentally chopped up in salads.” More so, shellfish, crabs, lizards, and frogs can act as hosts that lead to subsequent infection.
In humans, an A. cantonensis infection can cause angiostrongyliasis (also referred to as neuroangiostrongyliasis or rat lungworm), a parasitic infection affecting the brain and spinal cord. Neuroangiostrongyliasis can lead to eosinophilic meningoencephalitis, which is a kind of meningitis defined by the “presence of at least 10% eosinophils in the total cerebrospinal fluid (CSF) leukocyte count,” according to ScienceDirect.
In general, a parasitic infection is typically at the root of the eosinophilic meningoencephalitis, with A. cantonensis being one of the main three infections that cause it. It cannot be passed from human to human.
What the study’s findings mean for MDs
While not common, the CDC notes that A. cantonensis in urban populations could threaten humans and health. Labus went on to say that most infections occur in Southeast Asia but that rare cases have been found in certain areas in the United States—likely due to being transported by ship from overseas.
“The authors of this study identified Angiostrongylus cantonensis in a population of brown rats in Georgia, showing that the infection can now be found in nature in an area where it had not previously been identified,” Labus says. “However, it had been found previously in the neighboring states of Florida and Alabama, so this isn't a surprise.”
Angiostrongylus cantonensis has also been found in Hawaii.
Patients shouldn’t worry too much if they read worrisome news articles about it. “Cases are very rare,” Labus says. “For the average person, this isn't something they will ever come in contact with. Doctors aren't going to see it in their practice, although it is something to consider if they are working through the diagnosis of eosinophilic meningitis.”
A patient’s exposure to certain foods, such as snails, slugs, and other foods.
A patient’s travel history.
Symptoms of angiostrongyliasis, such as gastrointestinal issues, headache, neurological symptoms, a constant headache, neck stiffness, tingling skin, or seizures. Presentation varies.
Eosinophils in the CSF.
A polymerase chain reaction (PCR) test.
PCR, dot blot ELISA, or western blot (if available).
Gnathostomiasis and baylisascariasis as a differential diagnosis for eosinophilic meningitis.
“Human infections are usually asymptomatic or very mild—but the worm can travel to the brain and cause life-threatening symptoms,” Labus says. The presentation of angiostrongyliasis will vary depending on the parasitic load; many patients will improve spontaneously, while others need supportive care, including pain management and steroids for inflammation.
Treating eosinophilic meningitis is also supportive but may also require steroids, lumbar puncture, and, at times, anthelmintics.