By Stan Deresinski, MD, FACP, FIDSA

Clinical Professor of Medicine, Stanford University

Dr. Deresinski reports no financial relationships relevant to this field of study.

SYNOPSIS: Excluding Hawaii, eosinophilic meningitis due to the rat lungworm rarely is encountered in the United States. Ordinarily, the infection is acquired in Asia and the South Pacific, but it also may be acquired in the southern United States.

SOURCE: Liu EW, Schwartz BS, Hysmith ND, et al. Rat lungworm infection associated with central nervous system disease — Eight U.S. states, January 2011-January 2017. MMWR Morb Mortal Wkly Rep 2018;67:825-828.

Most cases of infection with Angiostrongylus cantonensis, the rat lungworm, are acquired in Asia and the Pacific Islands, including Hawaii. Although the infection usually is asymptomatic, migration of the larvae can lead to serious complications, especially if they reach the central nervous system. Infections occasionally are diagnosed in the continental United States. Liu and colleagues reviewed 12 such cases with eosinophilic meningitis due to infection with this parasite, with the etiology determined by polymerase chain reaction (PCR).

The implicated sources of infection included raw vegetables, snails, and slugs. One individual had a history of geophagia. Six of the patients, all from southern states, denied any travel outside the continental United States.

Patients most often presented with subjective fever, weakness, headache, numbness, and/or tingling sensations. Among the findings on examination were cranial nerve deficits, nuchal rigidity, and focal weakness. Initial testing detected peripheral eosinophilia in 10 patients, and all 12 had cerebrospinal fluid (CSF) pleocytosis. CSF eosinophilia was absent on initial examination in only two patients, but was present on subsequent examination in both. Brain abnormalities were seen on MRI in eight of the 11 patients who underwent this examination, and spinal cord abnormalities were observed in five of six patients; one patient had optic nerve abnormalities.

Eleven patients received corticosteroids and seven received albendazole. Eleven of 12 patients improved (although it must be noted that whether this resulted from the therapeutic intervention is unknown), but four had continuing focal neurological abnormalities and one developed seizures five months later.

COMMENTARY

The only thing unusual about this report is that six of the 12 cases apparently were autochthonously acquired within the continental United States. The authors noted that A. cantonensis infection has been detected in snails (both native and exotic species) in Florida and Louisiana, and in rat species in these two states as well as in Oklahoma. Infections of opossums and nine-banded armadillos, among other vertebrates, also have been observed.

Despite the rarity of occurrence, these findings indicate that clinicians must keep in mind the possibility of infection with this parasite as a cause of eosinophilic meningitis, including among patients without a history of travel outside the continental United States. As an aside, there are other causes of eosinophilic meningitis that may be acquired within the United States, such as neurocysticercosis and coccidioidomycosis.