Seroepidemiology of Sarcocystis neurona and Neospora hughesi infections in domestic donkeys (Equus asinus) in Durango, Mexico

There is currently no information regarding Sarcocystis neurona and Neospora hughesi infections in donkeys in Mexico. Here, we determined the presence of antibodies against S. neurona and N. hughesi in donkeys in the northern Mexican state of Durango. Serum samples of 239 domestic donkeys (Equus asinus) were assayed for S. neurona and N. hughesi antibodies using home-made enzyme-linked immunoassays; six (2.5%) of the 239 donkeys tested seropositive for S. neurona. The seroprevalence of S. neurona infection was comparable among donkeys regardless of their origin, health status, or sex. Multivariate analysis showed that seropositivity to S. neurona was associated with increased age (OR = 2.95; 95% CI: 1.11–7.82; p = 0.02). Antibodies to N. hughesi were found in two (0.8%) of the 239 donkeys. Both exposed donkeys were healthy, 3- and 6-year-old females. This is the first evidence of S. neurona and N. hughesi infections in donkeys in Mexico.

A serosurvey of selected cystogenic coccidia in Spanish equids: first detection of anti-Besnoitia spp. specific antibodies in Europe

Background

Equine besnoitiosis, caused by Besnoitia bennetti, and equine protozoal myeloencephalitis (EPM), caused by Sarcocystis neurona and Neospora hughesi are relevant equine diseases in the Americas that have been scarcely studied in Europe. Thus, a serosurvey of these cystogenic coccidia was carried out in Southern Spain. A cross-sectional study was performed and serum samples from horses (n = 553), donkeys (n = 85) and mules (n = 83) were included. An in-house enzyme-linked immunosorbent assay (ELISA) was employed to identify a Besnoitia spp. infection and positive results were confirmed by an a posteriori western blot. For Neospora spp. and Sarcocystis spp., infections were detected using in-house ELISAs based on the parasite surface antigens N. hughesi rNhSAG1 and S. neurona rSnSAG2/3/4. Risk factors associated with these protozoan infections were also investigated.

Results

Antibodies against Besnoitia spp., Neospora spp. and Sarcocystis spp. infections were detected in 51 (7.1%), 46 (6.4%) and 20 (2.8%) of 721 equids, respectively. The principal risk factors associated with a higher seroprevalence of Besnoitia spp. were the host species (mule or donkey), the absence of shelter and the absence of a rodent control programme. The presence of rodents was the only risk factor for Neospora spp. infection.

Conclusions

This study was the first extensive serosurvey of Besnoitia spp. infection in European equids accomplished by two complementary tests and gives evidence of the presence of specific antibodies in these populations. However, the origin of the infection is still unclear. Further parasite detection and molecular genotyping are needed to identify the causative Besnoitia and Neospora species. Finally, cross-reactions with antibodies directed against other species of Sarcocystis might explain the positive reactions against the S. neurona antigens.

Electronic supplementary material

The online version of this article (doi:10.1186/s12917-017-1046-z) contains supplementary material, which is available to authorized users.

Prevalence of antibodies to Sarcocystis neurona and Neospora hughesi in horses from Mexico

Equine protozoal myeloencephalitis (EPM) is a debilitating disease of horses caused by Sarcocystis neurona and Neospora hughesi. Sera from 495 horses in Durango State, Mexico were tested for anti-protozoal antibodies using enzyme-linked immunosorbent assays (ELISAs) based on major surface antigens of these two parasites. Antibodies to S. neurona were detected in 240 (48.5%) of the 495 horse sera tested with the rSnSAG2/4/3 trivalent ELISA. Multivariate analysis showed that exposure to S. neurona was associated with age, feeding grains and crops, and small herd size. Antibodies to N. hughesi were found in 15 (3.0%) of the 495 horse sera tested with the rNhSAG1 ELISA and confirmed by Western blot of N. hughesi tachyzoite antigen. This is the first report of S. neurona and N. hughesi exposure in horses in Mexico, and it affirms that EPM should be in the differential diagnosis for horses exhibiting signs of neurologic disease in this country.

Improved detection of equine antibodies against Sarcocystis neurona using polyvalent ELISAs based on the parasite SnSAG surface antigens

Equine protozoal myeloencephalitis (EPM) is a common neurologic disease of horses that is caused by the apicomplexan pathogen Sarcocystis neurona. To help improve serologic diagnosis of S. neurona infection, we have modified existing enzyme-linked immunosorbent assays (ELISAs) based on the immunogenic parasite surface antigens SnSAG2, SnSAG3, and SnSAG4 to make the assays polyvalent, thereby circumventing difficulties associated with parasite antigenic variants and diversity in equine immune responses. Two approaches were utilized to achieve polyvalence: (1) mixtures of the individual recombinant SnSAGs (rSnSAGs) were included in single ELISAs; (2) a collection of unique SnSAG chimeras that fused protein domains from different SnSAG surface antigens into a single recombinant protein were generated for use in the ELISAs. These new assays were assessed using a defined sample set of equine sera and cerebrospinal fluids (CSFs) that had been characterized by Western blot and/or were from confirmed EPM horses. While all of the polyvalent ELISAs performed relatively well, the highest sensitivity and specificity (100%/100%) were achieved with assays containing the rSnSAG4/2 chimera (Domain 1 of SnSAG4 fused to SnSAG2) or using a mixture of rSnSAG3 and rSnSAG4. The rSnSAG4 antigen alone and the rSnSAG4/3 chimera (Domain 1 of SnSAG4 fused to Domain 2 of SnSAG3) exhibited the next best accuracy at 95.2% sensitivity and 100% specificity. Binding ratios and percent positivity (PP) ratios, determined by comparing the mean values for positive versus negative samples, showed that the most advantageous signal to noise ratios were provided by rSnSAG4 and the rSnSAG4/3 chimera. Collectively, our results imply that a polyvalent ELISA based on SnSAG4 and SnSAG3, whether as a cocktail of two proteins or as a single chimeric protein, can give optimal results in serologic testing of serum or CSF for the presence of antibodies against S. neurona. The use of polyvalent SnSAG ELISAs will enhance the reliability of serologic testing for S. neurona infection, which should lead to improved diagnosis of EPM.

Detection of equine herpesvirus-specific effector and memory cytotoxic immunity in the equine upper respiratory tract

Immunological protection of horses from equine herpesvirus-1 (EHV-1) infection and disease depends on the cooperation of virus-specific humoral and cellular immune responses. EHV-specific mucosal immunity may be an important component of such immune responses. This study demonstrates the induction of anti-EHV cytotoxic cellular immune responses in various mucosal and systemic lymphoid tissues associated with the upper respiratory tract (URT) of the horse. Four young horses (1-2 years of age) were inoculated intranasally with the Army 183 strain of EHV-1 and euthanized 1 week later. One untreated foal served as a non-infected control. Mucosa-associated tonsillar tissues, draining lymph nodes and PBMC were harvested. Virus-specific memory and effector cytolytic activity were individually assessed using 4 h chromium release assays, with and without in vitro restimulation with EHV-1, respectively. EHV-specific cytotoxic activity was detected ex vivo in several URT-associated mucosal lymphoid tissues of horses, particularly within the lining of the nasopharynx, a principal site of EHV-1 replication. This activity was also detected in the circulation of some horses 1 week post-challenge. Virus-specific memory cytotoxic activity was elevated in the circulation, and detectable in the draining lymph nodes of all horses following challenge infection.

Recombinant NhSAG1 ELISA: a sensitive and specific assay for detecting antibodies against Neospora hughesi in equine serum

Neospora hughesi is a recently identified cause of equine protozoal myeloencephalitis. However, the significance of this parasite is poorly understood. An enzyme-linked immunosorbent assay (ELISA) with a recombinant form of the N. hughesi 29-kDa surface antigen (rNhSAG1) was developed for serodiagnosis of equine N. hughesi infections. Parallel ELISA analysis showed that animals immunized or infected with N. hughesi exhibited greater antibody reactivity with rNhSAG1 than with the Neospora caninum homolog, rNcSAG1. The rNhSAG1 ELISA showed 94.4% sensitivity and 95.0% specificity when compared with N. hughesi western blot results for 1,006 samples. The N. hughesi seroprevalence was 3.4% for the 1,917 samples tested by ELISA, which is less than earlier reports. Importantly, western blot analysis of ELISA-positive sera revealed only 18 true seropositive samples for an even lower seroprevalence of 0.9%. These results imply that Neospora spp. infections are uncommon in horses. The sensitivity and specificity exhibited by the rNhSAG1 ELISA suggest that it has a potential use for serodiagnosis of N. hughesi infection in equids. Furthermore, the high-throughput capability of the ELISA will allow for screening large sample sets, which should provide a better understanding of N. hughesi epidemiology.

The mucosal humoral immune response of the horse to infective challenge and vaccination with equine herpesvirus-1 antigens

Equine herpesvirus-1 (EHV-1) remains a frequent cause of upper respiratory tract infection and abortion in horses worldwide. However, little is known about the local antibody response elicited in the upper airways of horses following exposure to EHV-1. This study analysed the mucosal humoral immune response of weanling foals following experimental infection with virulent EHV-1, or vaccination with either of 2 commercial vaccines. Twenty weanlings were assigned to 5 groups and were inoculated with, or vaccinated against, EHV-1 following different regimens. Finally, all weanlings were simultaneously challenged intranasally with virulent EHV-1 Army 183 (A183). Nasal wash and serum samples were collected at regular intervals until 13 weeks after final challenge. Nasal washes were assayed for EHV-1-specific equine IgGa, IgGb, IgG(T), IgA, IgM and total virus-specific antibody using an indirect, quantitative ELISA. Total serum antibody responses were also monitored, and clinical signs of EHV-disease were recorded for each individual. Virus-specific IgA dominated the mucosal antibody response elicited in weanlings inoculated with A183, being detectable at up to 3.1 microg/mg total IgA 13 weeks after challenge. Neither inactivated EHV-1 administered i.m., nor attenuated EHV-1 administered intranasally induced detectable mucosal antibodies. EHV-1-specific mucosal antibodies impeded EHV-1 plaque formation in vitro. Such virus-neutralising antibody probably contributes to a reduction of shedding of EHV-1 from the respiratory tract of virus-infected horses.

Use of lambda gt11 and monoclonal antibodies to map the genes for the six major glycoproteins of equine herpesvirus 1

To localize the genes for the major glycoproteins of equine herpesvirus 1 (EHV-1), a library of the EHV-1 genome was constructed in the lambda gt11 expression vector. Recombinant bacteriophage expressing EHV-1 glycoprotein epitopes as fusion products with beta-galactosidase were detected by immunoscreening with monoclonal antibodies specific for each of six EHV-1 glycoproteins. Seventy-four recombinant lambda gt11 clones reactive with EHV-1 monoclonal antibodies were detected among 4 X 10(5) phage screened. Phage expressing determinants on each of the six EHV-1 glycoproteins were represented in the library. Herpesviral DNA sequences contained in lambda gt11 recombinants expressing epitopes of EHV-1 glycoproteins were used as hybridization probes for mapping insert sequences on the viral genome. Genes for five EHV-1 glycoproteins (gp2, gp10, gp13, gp14, and gp21/22a) mapped to the genome L component; only one EHV-1 glycoprotein (gp17/18) was expressed from the unique S region of the genome where genes of several major glycoproteins of other herpesviruses have been located. Two glycoproteins of EHV-1, gp13 and gp14, mapped to positions colinear with genes of major glycoproteins identified in several other alphaherpesviruses (gC- and gB-like glycoproteins, respectively). The genomic locations of other EHV-1 glycoproteins indicated the existence of major glycoproteins of EHV-1 (gp2, gp10, and gp21/22a) for which no genetic homologs have yet been detected in other herpesviruses. The results confirm the general utility of the lambda gt11 expression system for localizing herpesvirus genes and suggest that the genomic positioning of several high-abundance glycoproteins of EHV-1 may be different from that of the prototype alphaherpesvirus, herpes simplex virus.

A new field strain of equine abortion virus (equine herpesvirus-1) among Kentucky horses

From restriction endonuclease characterization of the DNA of 317 isolates of equine abortion virus (equine herpesvirus-1; EHV-1) from 176 epizootically unrelated outbreaks of equine virus abortion occurring over 24 years in Kentucky, an epizootic pattern and variation of the virus have emerged. Two electropherotypes of EHV-1 (1P and 1B) accounted for greater than 90% of the nonvaccine-related abortion isolates examined. From 1960 to 1981, EHV-1 1P was the predominant isolate circulating in the central Kentucky area and the cause of greater than 80% of EHV-1-related abortions. In 1981, the occurrence of isolate 1B-related abortions began to increase and since 1982, 1B has become the most frequently recovered isolate of EHV-1 from aborted fetuses.

Alterations in the equine herpesvirus 1 genome after in vitro and in vivo virus passage

The effect of in vitro and in vivo serial virus passage on the genetic stability of equine herpesvirus 1 (EHV-1) was investigated by restriction endonuclease analysis of the viral DNA. DNAs of EHV-1 isolates at different passage levels in cultured cells or in Syrian hamsters were compared by electrophoresis of the DNA cleavage fragments produced by restriction endonuclease digestion. No changes were observed in the restriction profile of the DNAs of EHV-1 strains after 100 sequential passages in cultured equine cells. However, serial passage of the virus in hamsters or in cells of non-equine origin quickly gave rise to alterations in the viral DNA. These changes occurring in the restriction endonuclease profiles of EHV-1 DNA during serial virus passage in non-equine cells or animals hosts could be explained by sequence additions or deletions to preexisting restriction fragments resulting in variation in their electrophoretic mobilities.

Mammary transfer of vitamin E in cows treated with vitamin A or linoleic acid

The effect of an intravenous injection of vitamin A alcohol and subcutaneous injections of linoleic acid on the mammary transfer of an intravenous injection of vitamin E acetate was studied with 15 Holstein cows. The cows received either an intravenous injection of 3 g vitamin E acetate (controls), intravenous injections of 3 g vitamin E acetate and 1 million IU vitamin A alcohol, or an intravenous injection of 3 g vitamin E acetate and subcutaneous injections totaling 40 g of linoleic acid. Milk samples were at 12-h intervals, two prior to and six following treatment. The main influence of vitamin A alcohol and linoleic acid on mammary transfer of vitamin E was to delay secretion of vitamin E in milk. However, total secretion of vitamin E was not reduced by injection of either vitamin A alcohol or linoleic acid. Vitamin E injection produced substantial increases in vitamin E in milk, but less than 1% of the dose could be accounted for in the milk.