Protozoan infection may be more widespread in Europe’s equids than many believe – researchers

A: Two donkeys affected by besnoitiosis showed poor body condition and presented with dull and rough coats. B: Alopecia and hyperkeratosis on the neck of the female donkey. C: Baldness and hyperkeratosis on the hind leg of the male donkey. D: Alopecia on the pinnae of the female donkey. E: Numerous typical scleral pearls (indicated by the arrows) in the eye of the male donkey. Photos: Villa et al.

The distribution of equine besnoitiosis in Europe could be wider than expected, according to researchers.

Their warning about the parasitic disease follows confirmation of the infection in two donkeys in northern Italy.

Luca Villa and his fellow researchers, writing in the journal Protozoology, said besnoitiosis was an emerging parasitic disease of equids.

In equids, it is caused by the protozoan Besnoitia bennetti. The parasite’s life cycle is not completely clear. In fact, the definitive host and the mode of transmission in equine infections remain unknown.

Clinical signs and lesions are similar to those seen in besnoitiosis in cattle. White pinpoint parasitic cysts appear on the skin of the face and body, in the nostrils, on the ears, on the limbs, and in the area between the anus and genitals. The lesions are also frequently found on mucous membranes, particularly in the upper respiratory tract.

A typical feature of the disease is the development of parasitic cysts within the sclera and conjunctiva of the eye, known as scleral pearls.

Infected animals eventually develop a poor coat and skin lesions with bald patches, sparse hair, excess pigmentation, thickening, and crusting, involving the face, muzzle, eyes, ears, neck, flanks, legs, and between the genitals and anus.

Some infected donkeys remain otherwise healthy, while others can become debilitated.

The disease was historically limited to donkeys and horses in Africa, where outbreaks were reported in both species.

Outside of Africa, outbreaks have been reported in donkeys in the United States, where besnoitiosis may be considered an emerging disease of these equids.

In Europe, the first case in a horse was historically reported in northern France. Recently, the disease was suspected in seven donkeys from southern Spain, where tissue cysts were detected by microscopic examination. Clinical cases of besnoitiosis were also reported in two donkeys in Belgium and 20 in Britain. In both these reports, the diagnosis was confirmed through molecular-based testing.

Specific antibodies for Besnoitia parasites have been detected in equids in Spain, and also in Italy, where outbreaks of bovine besnoitiosis were previously reported.

Villa and his colleagues noted that Italy is one of the few European countries where the presence of Besnoitia antibodies has been shown. In their study, clinical besnoitiosis in two donkeys in northern Italy was confirmed through testing. The animals’ eyes were affected, as was their skin, with numerous small cysts.

Both animals were seropositive to Besnoitia antibodies, and parasitic DNA extracted from skin biopsies of both donkeys aligned with Besnoitia species (there are 10 recognised species).

“This first clinical case of besnoitiosis in two donkeys in Italy both confirms the circulation of Besnoitia species in Italian equids and demonstrates that the distribution area of equine besnoitiosis in Europe could be wider than expected,” they reported.

The study team said further work is needed to learn more about its seroprevalence and clinical disease, and to identify the species of Besnoitia infecting donkeys. “Besnoitiosis,” they said, “may be a neglected disease of donkeys in Europe.”

An early and accurate diagnosis is fundamental to implement adequate control measures to prevent its “silent” spread among equids, they said.

The two donkeys, a male and female, were also found to have a heavy burden of strongyles. They were dosed with ivermectin.

After hospital discharge, the donkeys were revisited four times, one month apart and regularly every six months. Their body condition was improved. However, seropositivity and all clinical signs of besnoitiosis were still present, as the disease cannot be cured.

The study team, discussing their findings, said epidemiological data, together with molecular results, suggest the donkeys could have been infected by B. besnoiti, the species known to infect cattle.

B. besnoiti has previously been detected in roe deer, suggesting it could be capable of infecting and causing clinical disease in species other than cattle.

Unfortunately, the study team had been unable to achieve a conclusive species identification in the two infected donkeys.

Besnoitiosis in equids could be almost as widespread as bovine besnoitiosis in Europe, the team cautioned. “However, due to difficulties in the diagnosis, besnoitiosis could be underdiagnosed and underreported, thus favoring a silent spread of the disease in European equids.”

Besnoitiosis should be included among differential diagnoses when detecting skin lesions in equids, they said.

The study team comprised Villa, Alessia Libera Gazzonis, Sergio Aurelio Zanzani, Francesco Ferrucci and Maria Teresa Manfredi, all with the University of Milan; Carlos Diezma-Diaz and Gema Álvarez-García, both with the Complutense University of Madrid; and Chiara Perlotti, of Brescia, Italy.

Villa, L., Gazzonis, A.L., Diezma-Diaz, C. et al. Besnoitiosis in donkeys: an emerging parasitic disease of equids in Italy. Parasitol Res 120, 1811–1819 (2021).

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

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