Protozoal coinfection in horses with equine protozoal myeloencephalitis in the eastern United States

Evidence of intrathecally-derived antibodies against Toxoplasma gondii in horses suspected of neurological disease consistent with equine protozoal myeloencephalitis

Among the recognized neurologic diseases in horses, equine protozoal myeloencephalitis (EPM) has been reported around the world and still presents challenges in diagnosis and treatment. Horses can present with clinical neurologic signs consistent with EPM while testing negative for the two main causative agents, Sarcocystis neurona or Neospora hughesi, and may still be clinically responsive to anti-parasitic drug therapy. This context led to our hypothesis that another protozoal parasite, Toxoplasma gondii, which is known to cause toxoplasmosis in other mammalian species, is a potential pathogen to cause neurologic disease in horses. To evaluate this hypothesis, serum and cerebrospinal fluid (CSF) were collected from 210 horses presenting with clinical signs compatible with EPM, and the indirect immunofluorescent antibody test (IFAT) was used to detect antibody titers for T. gondii, S. neurona, and N. hughesi. Additionally, the serum to CSF titer ratio was calculated for T. gondii, S. neurona, and N. hughesi infections, suggesting intrathecally-derived antibodies for each of the three agents if the serum:CSF ratio was ≤ 64. There were 133 (63.3%) horses positive for serum T. gondii antibodies using a cutoff titer of 160, and 31 (14.8%) positive for CSF T. gondii antibodies using a cutoff titer of 5. Overall, 21 (10.0%) of EPM-suspect horses had a serum:CSF ratio ≤ 64 for antibodies for T. gondii, while 43 (20.5%) and 8 (3.8%) horses had a serum to CSF ratio ≤ 64 for antibodies for S. neurona and N. hughesi, respectively. A total of 6 (2.9%) animals presented evidence of concurrent intrathecally-derived antibodies for T. gondii and at least one other apicomplexan parasite in this study. Signalment and clinical signs were not different across the groups aforementioned. These data provide evidence of intrathecal production of anti-T. gondii antibodies, indicative of T. gondii infection in the brain and/or spinal cord of horses with EPM-like disease.

Seroepidemiological study of Toxoplasma gondii in equids in different European countries

Toxoplasmosis, caused by the obligate intracellular protozoan Toxoplasma gondii, is a worldwide parasitic zoonosis. A cross-sectional study was carried out to determine the exposure to T. gondii in equids in Europe. Serum samples from 1399 equids (1085 horses, 238 donkeys, and 76 mules/hinnies) bred in four European countries (Italy, Spain, United Kingdom [UK], and Ireland) were collected during the period of 2013-2021. The overall seroprevalence of T. gondii was 18.9% (95% Confidence Interval [CI]: 16.9-21.0) by using the modified agglutination test (MAT) at a cut-off of 1:25. Seropositivity by country was 27.1% in Italy, 16.6% in Spain, 12.0% in UK and 7.0% in Ireland. Anti-T. gondii antibodies were detected in 12.8% of the horses, 43.7% of the donkeys, and in 28.9% of the mules/hinnies. A Generalized Estimating Equation (GEE) analysis was carried out to study the associations between seropositivity and explanatory variables related to individuals, herds, and management measures on these herds, selected based on the bivariate analysis. The risk for being seropositive for T. gondii was 5.3 and 2.7 times higher in donkeys and mules/hinnies than in horses, respectively. In addition, significantly higher seropositivity was observed in horses from herds that used disinfectants less than once a week (13.9%; p = 0.038, odds ratio [OR] = 1.6; 95% CI: 1.03-2.62) compared with those from herds that performed weekly disinfection of the facilities (9.4%). This is the first large-scale seroepidemiological study on T. gondii comprising horses, donkeys, and mules/hinnies in Europe and the first report of T. gondii exposure in horses from Ireland and UK. We found a widespread distribution of T. gondii among equid populations in different European countries. The seroprevalence found in these species, especially in donkeys and mules/hinnies, highlights the potential risk of human infection through the consumption of their raw/undercooked milk or meat.

Equine Protozoal Myeloencephalitis

Advances in the understanding of equine protozoal myeloencephalitis (EPM) are reviewed. It is now apparent that EPM can be caused by either of 2 related protozoan parasites, Sarcocystis neurona and Neospora hughesi, although S neurona is the most common etiologic pathogen. Horses are commonly infected, but clinical disease occurs only infrequently; the factors influencing disease occurrence are not well understood. Epidemiologic studies have identified risk factors for the development of EPM, including the presence of opossums and prior stressful health-related events. Attempts to reproduce EPM experimentally have reliably induced antibody responses in challenged horses, but have not consistently produced neurologic disease. Diagnosis of EPM has improved by detecting intrathecal antibody production against the parasite. Sulfadiazine/pyrimethamine (ReBalance) and the triazine compounds diclazuril (Protazil) and ponazuril (Marquis) are effective anticoccidial drugs that are now available as FDA-approved treatments for EPM.

Invited review: Sarcocystis neurona, Neospora spp. and Toxoplasma gondii infections in horses and equine protozoal myeloencephalitis (EPM): five decades of personal experience, perspectives, and update

Sarcocystis neurona, Neospora spp. and Toxoplasma gondii are related protozoans; they were considered the same parasite until 1970s. Two of these parasites, S. neurona and Neospora spp. are associated with a neurological syndrome in horses, called equine protozoal myeloencephalitis (EPM). The diagnosis and treatment of EPM are difficult. Most cases of EPM are related to S. neurona while only a few are due to Neospora spp. infections. There are two species of Neospora, Neospora caninum that has a wide host range and Neospora hughesi that has been found only in horses. Currently, T. gondii is not considered as a cause of EPM in horses, although it causes neurological illness in many other hosts, including humans. The present review provides an update on history, life cycle, diagnosis and treatment of these three infections in horses.

Global seroprevalence of Neospora spp. in horses and donkeys: A systematic review and meta-analysis

Neospora infections due to Neospora caninum and N. hughesi are prevalent among equids of the world. The disease may affect reproductive and neurological consequences. The present systematic review and meta-analysis was performed to evaluate the global Neospora seroprevalence among horses and donkeys. A number of 57 out of 1575 total retrieved studies were included by searching the PubMed, Scopus, Science Direct, Web of Science and ProQuest. A total of 25,783 horses and 4377 donkeys were examined serologically, yielding a weighted seroprevalence of 13.46 % (95 % CI: 10.26 %-17.42 %) globally. Subgroup analysis revealed that there were statistically significant differences in the overall prevalence of Neospora spp. in the examined animals according to year, continent, WHO region, country, host, and diagnostic method. Age and sex in horses as well as sex in donkeys were significantly associated with the Neospora seroprevalence (P < 0.001). Our findings showed a relatively high exposure to Neospora spp. in horses and donkeys worldwide. Considering the possible economic impact, as well as the importance in animal health, more studies are needed to clarify the species causing equine neosporosis, correlate serological findings with clinical outcomes and assess the risk factors, in order to define adequate prevention and control strategies.

Toxoplasma gondii infections in horses, donkeys, and other equids: The last decade

Toxoplasma gondii infections are common in humans and animals worldwide. The present review summarizes worldwide information on the prevalence of clinical and subclinical infections, epidemiology, and genetic diversity of T. gondii in horses, donkeys and other equids in the past decade. This review will be of interest to biologists, parasitologists, veterinarians, and public health workers.

Toxoplasma gondii infection and toxoplasmosis in farm animals: Risk factors and economic impact

The protozoan parasite Toxoplasma gondii is a zoonotic parasite that can be transmitted from animals to humans. Felids, including domestic cats, are definitive hosts that can shed oocysts with their feces. In addition to infections that occur by accidental oral uptake of food or water contaminated with oocysts, it is assumed that a large proportion of affected humans may have become infected by consuming meat or other animal products that contained infective parasitic stages of T. gondii. Since farm animals represent a direct source of infection for humans, but also a possible reservoir for the parasite, it is important to control T. gondii infections in livestock. Moreover, T. gondii may also be pathogenic to livestock where it could be responsible for considerable economic losses in some regions and particular farming systems, e.g. in areas where the small ruminant industry is relevant. This review aims to summarize actual knowledge on the prevalence and effects of infections with T. gondii in the most important livestock species and on the effects of toxoplasmosis on livestock. It also provides an overview on potential risk factors favoring infections of livestock with T. gondii. Knowledge on potential risk factors is prerequisite to implement effective biosecurity measures on farms to prevent T. gondii infections. Risk factors identified by many studies are cat-related, but also those associated with a potential contamination of fodder or water, and with access to a potentially contaminated environment. Published information on the costs T. gondii infections cause in livestock production, is scarce. The most recent peer reviewed reports from Great Britain and Uruguay suggest annual cost of about 5-15 million US $ per country. Since these estimates are outdated, future studies are needed to estimate the present costs due to toxoplasmosis in livestock. Further, the fact that T. gondii infections in livestock may affect human health needs to be considered and the respective costs should also be estimated, but this is beyond the scope of this article.

Gastrointestinal parasite infestation in the alpine mountain hare (Lepus timidus varronis): Are abiotic environmental factors such as elevation, temperature and precipitation affecting prevalence of parasite species?

Information concerning factors regulating Alpine mountain hare (Lepus timidus varronis) populations such as host-parasite interactions is missing as only a few parasitological surveys exist of this subspecies. Parasites are not only dependent on their host but also on suitable environmental conditions for infestation. Abiotic environmental factors have an important regulating role on parasites in mammals. It is estimated that the elevation range of parasites is likely to shift in response to alternate host movement and changes in climate. Here we assess the parasitic infestation in the Alpine mountain hare by analysing the parasites in faeces and comparing the parasite infestation at different elevation ranges and at varied weather conditions for two years in the Austrian Alps. Almost half of the faecal samples were free of parasites (46.2%, n = 52). Most frequent was the infection by Coccidia (46.2%), whereas stomach intestine strongylids, Trichuris spp, and Cestoda were only found in 9.6% of all faeces. Hence, only Coccidia may be prevalent enough to regulate Alpine mountain hare populations in the Austrian Alps. Elevation had a significant positive effect on the infection of animals by Trichuris spp, whereas temperature had a significant negative effect on the infection by any parasite traceable in faeces and, when looking at the parasite groups individually, on Coccidia.

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Almost half of the Alpine mountain hare faecal samples were free of parasites.

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Coccidia was more frequent in our hare faeces than in other examined populations.

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Stomach intestine strongylids and Cestoda were only found in 9.6% of our samples.

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Only Coccidia may be prevalent enough to regulate this hare population.

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Temperature had a significant negative effect on the incidence of any parasite in the faecal samples.

Protozoal coinfection in horses with equine protozoal myeloencephalitis in the eastern United States

Background

Infection by 2 or more protozoa is linked with increased severity of disease in marine mammals with protozoan encephalitis.

Hypothesis/Objectives

To assess whether horses with equine protozoal myeloencephalitis (EPM) caused by Sarcocystis neurona also have evidence of infection with Neospora hughesi or Toxoplasma gondii. We hypothesized that horses with EPM would be more likely than horses with cervical vertebral stenotic myelopathy (CVSM) to be positive for antibodies to multiple protozoan parasites.

Animals

One hundred one horses with neurologic disease: 49 with EPM and 52 with CVSM.

Methods

Case review. Archived serum and cerebrospinal fluid (CSF) from 101 horses were examined. Inclusion criteria included neurologic disease, antemortem or postmortem diagnosis of EPM or CVSM, and availability of serological results or archived samples for testing. Additional testing for antibodies was performed on serum for T. gondii, as well as serum and CSF for N. hughesi.

Results

Horses with EPM were more likely than horses with CVSM to have positive immunologic results for S. neurona on serum (95.9% versus 76.9%, P = .0058), CSF (98.0% versus 44.2%, P < .00001), and serum : CSF titer ratio (91.8% versus 0%, P < .00001). Positive results for Neospora and Toxoplasma were uncommon, with total seroprevalence rates of 12.9% and 14.9%, respectively. The proportions of EPM cases testing positive for Neospora and Toxoplasma (16% and 12%) were not different from the proportions of CVSM cases testing positive (10% and 17%, P = .31 and .47, respectively).

Conclusion

Results do not indicate an important role for protozoal coinfection in EPM in the eastern United States.