Novel description of force of infection and risk factors associated with Theileria equi in horses in Israel and in The Palestinian Authority

Serological and Molecular Prevalence of Babesia caballi in Apparently Healthy Horses in Israel

Babesia caballi is a tick-borne hemoparasite of equines and one of the causative agents of equine piroplasmosis, which poses a great concern for the equine industry regarding animal welfare and international horse movement. The parasite is endemic in Israel; however, its seroprevalence in the area was never evaluated due to antigenic heterogenicity in the gene used in the commercially available kit. Blood samples were collected from 257 horses at 19 farms throughout the country and screened for the presence of anti-B. caballi antibodies via an indirect immunofluorescent antibody test (IFAT) and for the presence of parasite DNA by nested PCR. The seroprevalence of B. caballi was 69.6% and its molecular prevalence was 9.7%. The geographical area, horse’s sex, breed, housing, exposure to ticks, and specifically to Hyalomma marginatum, and co-infection with Theileria equi were found to be significantly associated with serologic exposure in univariable analysis, while the geographical area and horses’ sex remained significant in the multivariable analysis. The results of this study demonstrate a high level of exposure to B. caballi and identify important risk factors for infection. The difference between the serological and molecular prevalence, probably related to parasite clearance, is also highlighted.

Twenty Years of Equine Piroplasmosis Research: Global Distribution, Molecular Diagnosis, and Phylogeny

Equine piroplasmosis (EP), caused by the hemoparasites Theileria equi, Theileria haneyi, and Babesia caballi, is an important tick-borne disease of equines that is prevalent in most parts of the world. Infection may affect animal welfare and has economic impacts related to limitations in horse transport between endemic and non-endemic regions, reduced performance of sport horses and treatment costs. Here, we analyzed the epidemiological, serological, and molecular diagnostic data published in the last 20 years, and all DNA sequences submitted to GenBank database, to describe the current global prevalence of these parasites. We demonstrate that EP is endemic in most parts of the world, and that it is spreading into more temperate climates. We emphasize the importance of using DNA sequencing and genotyping to monitor the spread of parasites, and point to the necessity of further studies to improve genotypic characterization of newly recognized parasite species and strains, and their linkage to virulence.

Sero-molecular survey and risk factors of equine piroplasmosis in horses in Spain

BACKGROUND

Theileria equi and Babesia caballi cause equine piroplasmosis (EP), one of the most important tick-borne diseases of horses due to its high negative impact to the equine industry. Although infections with these parasites have been reported for decades in Spain, epidemiological studies have only been carried out in certain regions.

OBJECTIVES

To determine the (sero)prevalence of these parasites in asymptomatic horses nationwide in Spain and to identify potential individual and environmental factors associated with seropositivity to EP.

STUDY DESIGN

Sample size was calculated according to the horses registered in Spain in 2013 and by autonomous community using a random stratified sampling. A questionnaire was used to collect data on factors associated with EP seropositivity.

METHODS

Serological (cELISA and complement fixation test) and molecular (real-time PCR) analyses were carried out in 740 horses. Risk factors were identified computing two independent logistic regression models with the collated data.

RESULTS

Antibodies against EP were detected in 42.9% (95% CI 39.4-46.5) of horses, whereas 30.3% (95% CI 27.0-33.6) were EP positive by PCR. A substantial strength of agreement (k = 0.721) was estimated between serological tests. Exposure to T. equi was significantly higher than to B. caballi and the highest (sero)prevalence was detected in the northern communities. Increasing horse age, presence of ticks and contact with cows were factors related to EP seropositivity in the horses, whereas tetanus vaccination and fairs attendance were associated with lower seropositivity.

CONCLUSIONS

Almost half of the horses residing in Spain had antibodies against EP or circulating parasitaemia. Appropriate prevention measures and implementation of a EP surveillance programme should be considered in order to reduce and control the infection.

Potential tick vectors for Theileria equi in Israel

Theileria equi Mehlhorn and Schein, 1998 (Piroplasmida: Babesiidae) is an important tick-borne pathogen of horses that is highly endemic in many parts of the world, including Israel. The present study evaluated the potential roles of five hard tick species [Hyalomma excavatum Koch, 1844; Hyalomma marginatum Koch, 1844; Rhipicephalus turanicus Pomerantsev 1936; Rhipicephalus annulatus Say, 1821; Haemaphysalis parva (Neumann, 1897) (all: Ixodida: Ixodidae)], previously found to infest horses in Israel, in acting as vectors for piroplasmosis. For this, DNA was extracted from whole ticks and, when possible, from the salivary glands in each species (n = 10-59). Polymerase chain reaction amplification and sequencing of the 18S rRNA gene were used to detect T. equi in 48 of the 127 ticks (37.8%) and in 21 of the 90 extracted salivary glands (23.3%) in all five species. All but two sequences were classified as T. equi genotype A; the remaining two were classified as genotype D. The findings of this study point to Ha. parva and R. annulatus as potential novel vectors of T. equi, and suggest that parasite genotype selection occurs within the tick vector.

Infection dynamics of Theileria equi in carrier horses is associated with management and tick exposure

The tick-borne equine hemoparasite, Theileria equi, is endemic in many parts of the world where prevalence may be high, and most infected horses are apparently healthy but serve as life-long carriers. To determine the factors that affect T. equi dynamics, we followed parasitic loads in apparently healthy horses at four time points during one year. A total of 1094 blood samples were collected from 395 horses, along with ticks and demographic and clinical data. Infection and load of T. equi were tested by PCR and qPCR, and for the spring dataset, infection was also tested serologically by IFAT (n = 268). Theileria equi was molecularly detected in 64.8 % of the horses. The agreement between molecular and serological results was 79.8 % (K > 0.674) and positively correlated with parasitic load. Infection was associated with pale mucus membranes, lower packed cell volume and higher total solids (all P < 0.001), although these changes had only minor clinical importance. While parasitic loads in qPCR-positive samples (n = 561) were generally low (mean = 7.9-10^-4% parasitized erythrocytes), younger horses showed higher loads, possibly suggesting development of immunity. Infection and parasitic load were associated with housing management and tick exposure, illustrating different patterns of exposure. Endemic stability is suggested in pasture farms with constant exposure to ticks, where parasite prevalence was high (96 %) and associated with T. equi 18S rRNA genotype D, low parasitemia and high antibody titers. Endemic instability can be suggested in case were horses are kept in paddocks (prevalence = 49 %) with intermittent exposure to ticks, where infection was associated with high parasitemia when ticks were present. A steady state is suggested in stabled horses (prevalence = 46 %), with no exposure to ticks; where infection was associated with genotype A, low parasitemia and low antibody titers. The ability to identify different risk groups within endemic areas may improve the administration of suitable treatment and control practices in an effort to reduce the risk of clinical disease.

Transplacental Transmission of Theileria equi Is Not a Common Cause of Abortions and Infection of Foals in Israel

Although the main route of transmission of Theileria equi is through tick feeding, transplacental transmission is also possible and may lead to abortion, or to the birth of a sick or carrier foal. The aim of this study was to evaluate the role of T. equi as a cause of abortions in Israel and the risk of foals being infected at a young age. Eight aborting mares were serologically evaluated for exposure to T. equi via the immunofluorescence antibody test (IFAT) and their aborted fetuses were evaluated using PCR and qPCR. In addition, five mares and their foals (aged 4-6 months) from a highly endemic farm were tested for T. equi infection using IFAT, PCR and qPCR. Five of the eight aborting mares were seropositive for T. equi; however, none of the aborted fetuses was infected. All five mares from the endemic farm were subclinically infected with T. equi. Of their five foals, one was infected, with relatively high parasitemia and different parasite genotype than its dam's, suggesting another source of infection. The results of this study suggest that transplacental transmission of T. equi is not common and does not appear to be a prominent cause of abortion in chronically infected mares.

Serological detection and risk factors for equine piroplasmosis in the semiarid region of Pernambuco, Northeastern Brazil

Equine piroplasmosis, an economically important disease in horses, has so far not been reported in Pernambuco state, Brazil. This study aimed to evaluate the seroprevalence of anti-Babesia caballi and anti-Theileria equi antibodies based on the detection of these agents in equine blood and in ticks on horses in the municipality of Petrolina, Pernambuco, northeastern Brazil. Blood samples were drawn from 393 horses and sera were examined by ELISA. The presence of tick infestations was evaluated, and 101 ticks were subjected to DNA amplification for the detection of Babesia spp. by polymerase chain reaction (PCR). No parasites were detected in the blood smears. Anti-B. caballi and anti-T. equi antibodies were found in 27.2% (107/393) and 34.8% (137/393) horses, respectively. Infestation by Dermacentor nitens was detected in 4.3% (17/393) of the horses. There was no DNA amplification of the agents in ticks. The risk factors for the presence of anti-T. equi antibodies (P < 0.05) were: purebred (P < 0.001), animals older than 156 months (P = 0.014), and the presence of ticks (P = 0.001). No risk factors for B. caballi were identified. This study confirmed the circulation of agents of equine piroplasmosis in the municipality of Petrolina, state of Pernambuco, Brazil.

Stress conditions do not affect Theileria equi parasitemia levels in sub-clinically infected horses

Stress has been suggested as a risk factor for Theileria equi peracute disease and may lead to relapse in clinical signs in chronically infected horses. The aim of this study was to assess the effect of stress on T. equi parasitemia in sub-clinically infected horses in two settings: horses hospitalized at a veterinary teaching hospital and horses from an endurance farm. Blood samples were collected from the hospitalized horses (n = 32) upon admission (T0) and at discharge (T1) from the hospital, and results were compared between horses that underwent surgery (stress) and other hospitalized horses (control). Blood samples were collected from an endurance farm (n = 20) six weeks before (T0) and two days after (T1) participation in an 80-km endurance event, and results were compared between horses that participated (stress) or did not participate (control) in the event. Theileria equi parasite load was determined using qPCR, and T1/T0 ratio was calculated for each horse. Mean parasite load at both time points did not differ statistically between the stress group and the controls in both settings. Theileria equi genotype was determined based on the 18S rRNA gene, when possible. Parasite genotypes were similar to strains previously characterized in the region and classified as genotypes A and D. The results of this study contradict the common assumption that stress may lead to increased parasite load in horses with a subclinical T. equi infection.

Analysis of Theileria equi diversity in The Gambia using a novel genotyping method

Theileria equi, one of the primary pathogens causing equine piroplasmosis, has previously been sub-classified into a number of clades on the basis of 18S SSU rRNA gene sequence diversity. This partitioning of the parasite population has potential implications for host immunity, treatment and vaccine development. To detect and identify different clade genotypes among and within individual equine blood samples, a novel PCR-based technique was designed and optimized. Theileria equi has only recently been described in The Gambia, and the developed genotyping technique was used to analyse blood samples taken from 42 piroplasmosis-positive horses and donkeys within the country. Three different T. equi genotypes were detected within the population, including the same genotype as the recently described Theileria haneyi, with 61.9% of individuals found to be infected with more than one genotype. Overall, there was a trend that males were more likely to have a multiple genotype infection. Thus, the novel genotyping technique has been shown to be effective in analysis of field populations and offers researchers a rapid method of identifying multiple T. equi genotypes both within individuals and equine populations in epidemiological studies.

Genetic characteristics of Theileria equi in zebras, wild and domestic donkeys in Israel and the Palestinian Authority

Equine piroplasmosis (EP) is an important tick-borne disease of equids, caused by Theileria equi and Babesia caballi. It is endemic in most parts of the world, including Israel, and has clinical and economic consequences. This study was set to evaluate the presence of EP parasites in domestic donkeys and in wild equids in Israel and the Palestinian Authority (PA). To assess subclinical EP infection in 98 domestic donkeys (Equus africanus asinus), 9 Asiatic wild donkeys (Equus hemionus), 8 zebras (Equus quagga), 7 African wild donkeys (Equus africanus) and 5 mules, were tested using PCR and qPCR. Positive samples were characterized by amplification and sequencing of a 1600 bp fragment of the 18S rRNA gene. Babesia caballi was not detected in any of the animals. Theileria equi was detected in 32% of the donkeys, 89% of Asiatic wild donkeys, 57% of African wild donkeys, 62% of zebras and none of the mules. Parasitemia was low in all of the positive samples. Risk factors associated with infection in donkeys included one farm (Kiryat Gat) and animal sex (male). The sequences of the 18S rRNA gene from domestic donkeys were all similar, and belonged to the T. equi genotype D, similar to the genotype sequenced from horses in the same area, while sequences from wild donkeys were unique and belonged to the T. equi genotype A. Verification of the T. equi genotype in zebras could not be concluded, suggesting major genetic variation.

Species distribution and seasonal dynamics of equine tick infestation in two Mediterranean climate niches in Israel

Background

Ticks are important ectoparasites of horses that can affect animal welfare and vector several infectious, including zoonotic, diseases. In order to investigate the species distribution, epidemiology and seasonal dynamics of ticks infesting horses in Israel, 3267 ticks were collected from 396 horses in 24 farms across the country from July 2014 to June 2015.

Results

Ticks were found on 50% of the farms and on 25% of the horses, with Hyalomma being the most prevalent genus (70% of ticks). Pasture was the most prominent risk factor for tick infestation (99% of ticks, P < 0.001), and is represented here by two areas with a Mediterranean climate that differ in their environmental characteristics: the Golan Heights (GH, 74% of ticks); and the Carmel mountain ridge (CMR, 24%). Although these two sites are less than 100 km apart, the composition of the tick populations infesting horses differed significantly between them. In GH the most abundant tick species was Hyalomma excavatum (P < 0.001), while in CMR it was Hyalomma marginatum (P < 0.001). The GH also hosted a more diverse tick fauna than the CMR, including Haemaphysalis parva (peaking in the autumn, P < 0.001) and Rhipicephalus turanicus (peaking in the spring, P < 0.001), which were not found at the other sites. A few Rhipicephalus bursa, Hyalomma rufipes and Hyalomma turanicum were also found on horses.

Conclusions

The current findings can be used in epidemiological studies assessing the risk of tick-borne equine diseases in the area. Further analysis is needed to determine the specific distribution and habitat preferences of each tick species.

Electronic supplementary material

The online version of this article (10.1186/s13071-018-3093-0) contains supplementary material, which is available to authorized users.

Seroprevalence of Theileria equi and Babesia caballi in horses in Spain

Equine piroplasmoses are enzootic parasitic diseases distributed worldwide with high incidence in tropical and subtropical regions. In Spain, there is insufficient epidemiological data about equine piroplasmoses. The main aim of the present study was therefore to estimate the prevalence of Theileria equi and Babesia caballi in five regions and obtain information about the risk factors. This study was conducted in the central and south-western regions of Spain, using indirect fluorescence antibody testing (IFAT) in 3,100 sera samples from apparently healthy horses of different ages, breeds, coat colours, genders and geographical locations. The overall seroprevalence was 52%, consisting of 44% seropositive for T. equi and 21% for B. caballi. There was a significant association between age (p < 0.0001), breed (p < 0.004), geographical location (p < 0.0001) and the seroprevalence, but neither the coat colour nor the gender was significantly associated with prevalence. In addition, it was proved that most of the geographic areas showed a moderate to high prevalence. The statistical κ value was used to compare the results obtained by the IFAT and the competitive enzyme-linked immunosorbent assay (cELISA) utilised to test some samples (n = 108) and showed a higher concordance for T. equi (κ = 0.68) than for B. caballi (κ = 0.22). Consequently, this revealed the importance of developing an appropriate technique to detect each haemoparasite.