Angiostrongylus cantonensis Infection in Brown Rats (Rattus norvegicus), Atlanta, Georgia, USA, 2019–2022

Rat lungworm (Angiostrongylus cantonensis), a zoonotic parasite invasive to the United States, causes eosinophilic meningoencephalitis. A. cantonensis harbors in rat reservoir hosts and is transmitted through gastropods and other paratenic hosts. We discuss the public health relevance of autochthonous A. cantonensis cases in brown rats (Rattus norvegicus) in Atlanta, Georgia, USA.

Our molecular analysis confirmed the identity of A. cantonensis in 4/7 samples that had nematodes visible on histologic examination of heart, pulmonary artery, and brain tissues (Table ).All 4 sequences were 100% identical to each other and to A. cantonensis sequences belonging to haplotype 17a, previously reported from Louisiana, USA.Among homologous sequences available in Gen-Bank from A. cantonensis isolates from the United States, those belonging to haplotype 17b (Louisiana and California) were 99.5% similar, haplotype 8b (Louisiana) 98.9% similar, and haplotype 5a (Hawaii) 98.9% similar to those in haplotype 17a.Overall, compared with other A. cantonensis haplotypes included in the phylogenetic analysis, similarity of sequences ranged from 93.1%-99.5%,clustering in a clade with 86% bootstrap support (Appendix, https//wwwnc.cdc.gov/EID/article/29/10/23-0706-App1.pdf).

Conclusions
Discovery of autochthonous cases of A. cantonensis infection in definitive host rodents collected during 2019-2022 in the state of Georgia suggests that this zoonotic parasite was introduced to and has become established in a new area of the southeastern United States.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.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.
Because A. cantonensis lungworm previously was identified in rats in neighboring states Florida and Alabama, A. cantonensis populations likely were in Georgia much earlier than 2019, when the first positive rat was identified in Atlanta.Furthermore, 6 suspected autochthonous human angiostrongyliasis cases were detected during 2011-2017 in Texas, Tennessee, and Alabama (10).Among captive wildlife, A. cantonensis lungworm has been reported in nonhuman primates in Florida (11), Louisiana (7,12), Texas (4), and Alabama (13), and a red kangaroo in Mississippi ( 14).Among free-ranging wildlife native to the southeastern United States, A. cantonensis infections have been identified in armadillos and an opossum (15).
Various native and exotic gastropod species have been shown, both naturally and experimentally, to be susceptible intermediate hosts (3,5,11).Although details of A. cantonensis invasion and spread are not fully known, identification of introduced gastropods as intermediate hosts (11) and Cuban tree frogs as paratenic hosts (6) in the southern United States suggest anthropogenic disturbance and climate-induced change in local food webs might be amplifying A. cantonensis transmission.Clearly, A. cantonensis lungworm in urban rat populations, gastropod intermediate hosts, and other paratenic hosts in the populous greater Atlanta area pose a possible threat to the health of humans and domestic, free-ranging, and captive animals.
Understanding patterns of historic, contemporary, and future expansion of the range of A. cantonensis lungworm in North America through surveillance, genetic analysis, and modeling is critical to mitigating risk to humans and other animals for infection by this parasitic nematode, which harbors in synanthropic wild rodent and intermediate host populations.Medical and veterinary professionals throughout the southern United States should consider A. cantonensis infection in differential diagnoses of aberrant central nervous system larva migrans, eosinophilic meningitis, and meningoencephalitis.

About the Author
Dr. Gottdenker is professor in the Department of Pathology at the University of Georgia College of Veterinary Medicine, Athens, GA, USA.Her research focuses on pathology and ecology of wildlife diseases, including zoonotic parasites, and the effects of anthropogenic environmental changes on disease ecology and evolution.

Figure .
Figure.Brain and lung tissue samples showing Angiostrongylus cantonensis infection in brown rats (Rattus norvegicus), Atlanta, Georgia, USA, 2019-2022.A) Representative tissue section from the brain, stained with hematoxylin and eosin.The meninges and ventricles are multifocally and moderately expanded by abundant hemorrhage.Within the meninges and ventricles, occasional cross sections through nematodes can be seen.Nematodes were ≈250-300 µm in diameter with a thin eosinophilic cuticle, pseudocoelom, polymyarian coelomyarian musculature, lateral chords, and multinucleated intestine.Original magnification ×200 µm.B) Representative tissue section from the lung stained with hematoxylin and eosin.A large pulmonary artery contains fragments of a degenerative nematode characterized by a thin eosinophilic cuticle, pseudocoelomic space, and polymyarian coelomyarian musculature.The subtending arterial wall was sometimes necrotic and variably infiltrated by eosinophils, lymphocytes, and macrophages.The vessel also displays hypertrophy of the tunica media and occasional hypertrophy of the endothelial cells.Original magnification ×100 µm.

Table .
Histopathologic findings of Angiostrongylus cantonensis nematode infection and molecular confirmation in brown rats (Rattus norvegicus), Atlanta, Georgia, USA, 2019-2022* *Pre-or postmortem predation of some rats might have occurred before rats were found.Thus, representative samples of all organs might not have been available for evaluation and in some cases, sex or age class could not be determined.ID, identification; NA, not available.