Opportunistic parasite attacked brain of horse, researchers report

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H. gingivalis is shown in the horse's brain tissue. The image at left shows an isolated larva of H. gingivalis and the image at right shows a pregnant female.
H. gingivalis is shown in the horse’s brain tissue. The image at left shows an isolated larva of H. gingivalis and the image at right shows a pregnant female.

A horse that died from neurological problems thought to have been caused by West Nile Virus was later found to be infected by an opportunistic parasitic worm which had damaged its brain.

The case of Halicephalobus gingivalis infection in Italy has been described in the March 7 issue of Parasites & Vectors.

Barbara Iulini and her colleagues said the 2012 case was reported in a 13-year-old stallion that had been born in the Netherlands.

It arrived in Italy in 2004, where it had lived with other healthy horses in the province of Turin, in the Piedmont region.

The animal was presented for examination with a two-day history of severe and rapidly progressing neurological problems.

Clinical signs included fever, circling, and a depressed mental state that alternated with hyperexcitability. It also had a right side head tilt.

Sedation and drug treatment was started but the horse’s condition continued to deteriorate, resulting in it being euthanized.

A necropsy (post mortem examination) revealed inflammation and damage to brain tissue which further analysis revealed was a result of infection by H. gingivalis. Larvae and adult females of the opportunistic pathogen were isolated and identified from brain tissue.

Testing for West Nile Virus proved negative.

H. gingivalis is a common freeliving nematode capable of infecting and reproducing in horses, zebras, donkeys, and humans. It has been isolated from soil, plants, or moist organic-rich habitats, such as swamps and in compost.

Cases of horses infected by H. gingivalis have been reported in a range of countries, suggesting its widespread distribution.

Only eight fatal cases have been reported in humans, with five in the United States, and one each in Canada, Australia and Germany. All known cases in humans involved the central nervous system and neurological problems.

The parasite tends to favor organs in horses and humans with good blood flow, such as the brain and kidney. It probably migrates through the blood vessels.

The study team said the source of the horse’s infection was not identified. The soil on the farm where the horse lived was not investigated for the presence of the parasite.

“Both the owner and the referring veterinarian reported that neurological clinical signs have never been observed in this or any other horses on the farm and there was no history of travel outside Piedmont,” they reported.

The researchers noted that nothing was known about the distribution of H. gingivalis in Italy but it could be more widespread than previously thought.

They said that Italy’s West Nile monitoring plan, which requires the testing of blood and organs from every horse with neurological signs to exclude the virus infection, could play a role in improving knowledge of neurological disorders in horses and their causes. It could also help to understand the geographic distribution of the H. gingivalis and the risk it poses to humans.

The case-report team comprised Iulini, Maria Domenica Pintore, Francesco Cerutti, Antonio D’Angelo, Cristiano Corona, Paola Gazzuola, Loretta Masoero, Corrado Colombo, Roberto Bona, Carlo Cantile, Simone Peletto and Cristina Casalon. They are affiliated with a range of Italian institutions.

Isolation and molecular characterisation of Halicephalobus gingivalis in the brain of a horse in Piedmont, Italy
Maria Domenica Pintore, Francesco Cerutti, Antonio D’Angelo, Cristiano Corona, Paola Gazzuola, Loretta Masoero, Corrado Colombo, Roberto Bona, Carlo Cantile, Simone Peletto, Cristina Casalone and Barbara Iulini.
Parasites & Vectors 2017 10:135 DOI: 10.1186/s13071-017-2070-3

The case report, published under a Creative Commons License, can be read here

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