Diagnosing a rare human disease in Mexico’s lowlands

Roundworms (Nematoda) are one of the most diverse groups of invertebrates. Lagochilascaris minor, a parasitic nematode often found in wild cats such as jaguars and pumas, as well as in domestic cats and dogs, has only rarely been known to infect humans. However, a recent case in the Yucatan Peninsula has brought about a very unique collaboration between medical practitioners and scientists. Lagochilascaris minor has been reported in the Americas, commonly in South America where the eggs have been found in public parks¹. However, identifying L. minor with conventional methods can be misleading as they resemble other ascaridoid eggs. When a 23-year old man from a village in the forests of southern Quintana Roo state (Yucatan Peninsula) came into the local hospital in July 2016, physicians were surprised to find that a parasite had destroyed the mastoid apophysis, the lateral sinus, and part of the cerebellum. After a radical mastoidectomy and medical treatment for 63 days, the patient made a full recovery. After removal, the parasite was identified as L. minor using DNA barcodes and morphology. While the method of infection is uncertain, it is thought to be through direct exposure to the eggs or through the consumption of uncooked meat from wild animals.

While it has been a challenge to successful identify Nematoda using genetic markers in the past, high-quality DNA barcode sequences were obtained using semi-degenerate primers designed for micro-crustaceans². A comparison with 81 ascaridoids obtained from the Barcode of Life Data System (BOLD) revealed its position in a unique clade, most closely related to Baylisascaris procyonis. This is the first multidisciplinary study involving DNA barcodes as a diagnostic medical tool in a human patient. This field of research can be promising because we can get a precise identification of the parasites in any stage of their life cycle. Diagnosis using DNA barcoding will allow the recognition of the infection parameters, transmission, and more precise epidemiology of parasites. With this information, we can not only diagnose the disease but also prevent it by finding the infectious stages, the intermediate hosts, or the vectors in the environment. All sequences of Lagochilascaris are in the public project ‘NECHE Lagochilascaris from Yucatan’ in BOLD. This study is published in the Journal of Parasitology.

References:

1. de Moura MQ, Jeske S, Gallina T, Borsuk S, Berne MEA, Villela MM (2012) First report of Lagochilascaris (Nematoda: Ascarididae) eggs in a public park in Southern Brazil. Veterinary Parasitology 184(2-4): 359-361. https://doi.org/10.1016/j.vetpar.2011.09.019
2. Prosser SW, Velarde-Aguilar MG, Leon-Regagnon V, Hebert PD (2013) Advancing nematode barcoding: A primer cocktail for the cytochrome c oxidase subunit I gene from vertebrate parasitic nematodes. Molecular Ecology Resources 13(6): 1108-1115. https://doi.org/10.1111/1755-0998.12082