Development of an Indirect ELISA to Detect Equine Antibodies to Theileria haneyi

New insights in the diagnosis and treatment of equine piroplasmosis: pitfalls, idiosyncrasies, and myths

Equine piroplasmosis (EP) is a global tick-borne disease of equids caused by the intraerythrocytic apicomplexan parasites Theileria equi and Babesia caballi, and the more recently discovered Theileria haneyi. These parasites can be transmitted by several tick species, including Dermacentor, Hyalomma, and Rhipicephalus, but iatrogenic and vertical transmission are also common. Clinical signs of EP include poor performance, fever, icterus, abortions, among others, and peracute or acute forms of infection are associated with high mortality in non-endemic areas. EP is a reportable disease and represents an important barrier for the international trade of horses and other equids, causing disruption of international equine sports. Tick control measures, serological and molecular diagnostic methods, and parasiticidal drugs are currently used against EP, while vaccines remain unavailable. Since most acaricides used in equids are non-environmentally friendly and linked to drug resistances, this is considered as an unsustainable approach. Imidocarb dipropionate (ID) and buparvaquone (BPQ) are currently the main drugs used to control the disease. However, while ID has several side and toxic effects and recurrent failures of treatment have been reported, BPQ is less effective in the clearance of T. equi infection and not available in some countries. Thus, novel alternative and effective therapeutics are needed. While current trade regulations require testing equids for EP before exportation, the lack of standardized PCR tests and limitations of the currently recommended serological assays entail a risk of inaccurate diagnosis. Hereby, we propose a combination of standardized PCR-based techniques and improved serological tests to diminish the risks of exporting EP-infected animals making equid international trade safer. In addition, this review discusses, based on scientific evidence, several idiosyncrasies, pitfalls and myths associated with EP, and identifies weaknesses of current methods of control and gaps of research, as initial steps toward developing novel strategies leading to control this disease.

Diagnostic performance of a rapid immunochromatographic test for the simultaneous detection of antibodies to Theileria equi and Babesia caballi in horses and donkeys

BACKGROUND

Equine piroplasmosis is caused by two tick-borne protozoan parasites, Theileria equi and Babesia caballi,, which are clinically relevant in susceptible horses, donkeys, and mules. Moreover, equine piroplasmosis significantly constrains international trading and equestrian events. Rapidly diagnosing both parasites in carrier animals is essential for implementing effective control measures. Here, a rapid immunochromatographic test for the simultaneous detection of antibodies to T. equi and B. caballi was evaluated using samples from horses and donkeys collected in Greece, Israel, and Italy. The results were compared with an improved competitive enzyme-linked immunosorbent assay (cELISA) for detecting antibodies to both parasites using the same panel of samples.

METHODS

Blood samples were collected from 255 horses and donkeys. The panel consisted of 129 horses sampled at four locations in northern Greece, 105 donkeys sampled at four locations in Sicily, and 21 horses sampled at two locations in Israel. The rapid test and the cELISA were performed according to the manufacturer's instructions, and the results were subjected to a statistical analysis to determine the sensitivity and specificity of both tests and their association.

RESULTS

The immunochromatographic test provided a result within 15 min and can be performed in the field, detecting both pathogens simultaneously. The overall coincidence rate between the rapid test and the cELISA for detecting antibodies against T. equi was 93% and 92.9% for B. caballi. The rapid test's sensitivity, specificity, positive predictive value (PPV), and negative predictive value (NPV) for T. equi were above 91.5%. Sixteen samples were positive for both parasites in the rapid test and eight in the cELISA. Either test had no significant association between T. equi and B. caballi detection. The detection rates of both parasites were significantly higher in Italy than in Greece or Israel and in donkeys than in horses. The agreement for T. equi between the results of both tests was high in Greece (93.8%) and Italy (95.2%) and moderate in Israel (76.2%). For B. caballi, the specificity and NPV of the rapid test were high (94.2% and 98.3%, respectively), although the sensitivity and PPV were moderate (69.2% and 39.1%, respectively) due to the small sample size. However, for B. caballi, the sensitivity was higher with the rapid test.

CONCLUSIONS

The rapid test detected T. equi and B. caballi simultaneously in the field, potentially replacing laborious cELISA testing and is recommended for import/export purposes. The test can also be helpful for the differential diagnosis of clinical cases, since seropositivity may rule out equine piroplasmosis since it does not indicate current or active infection.

Theileria equi in the horses of Iran: Molecular detection, genetic diversity, and hematological findings

In all equids worldwide, Theileria equi and Babesia caballi are believed to be two important erythrocytic protozoa that cause equine piroplasmosis. In addition, it was recently discovered that Theileria haneyi is another potential equine piroplasmosis (EP) agent. Ixodid ticks are the major vectors of these parasites. Equine piroplasmosis is of international importance and affects enormously the equine industry. In this study, for the first time, molecular prevalence and genetic diversity of piroplasma parasites (T. equi and B. caballi) in horses from Fars province (south of Iran) were determined. Also, hematological alterations of naturally infected horses were analyzed. PCR positive horses showed anemia, thrombocytopenia, leukocytosis with a left shift of neutrophilia, and monocytosis. PCR results revealed that, from 133 blood samples of horses, 40 samples were positive (30.07%). The occurrence of T. equi in this area (30.07%) was more than the national average prevalence of T. equi (24.11%), but B. caballi prevalence in study area (0%) was less than the average of previous studies in Iran (5.47%). Our findings revealed that the T. equi was widespread in Fars province of Iran. PCR products of 18S rDNA and EMA-1 genes of T. equi strains were sequenced successfully. All 18S rDNA sequences collected in this experiment revealed 100% similarity together. According to the phylogenetic tree constructed using the 18S rDNA gene, Iranian T. equi is clustered with strains from Cuba (KY111762, KY111761) and USA (CP001669, JX177672). So, this could be concluded that T. equi studied in this research, and those strains are initiated from a common T. equi ancestor at an unknown time ago. Also, the phylogenetic tree based on EMA-1 gene demonstrated a genetically diverse population of Iranian T. equi strains (10 different genotypes). As EMA-1 is one of the most immunogenic antigens in this parasite, such variability could be a concern about the efficacy of T. equi vaccines. Finally, more studies on equine piroplasmosis in the provinces of the southern region of Iran are recommended to create a better vision of disease in this region.

Molecular and Serological Detection of Piroplasms in Horses from Nigeria

Equine piroplasmosis, an economically important disease of equids caused by the hemoprotozoan parasites Theileria equi, T. haneyi, and Babesia caballi, has a worldwide distribution. These parasites are transmitted by ixodid ticks. To improve the detection of horses in Nigeria exposed to piroplasm parasites, 72 horses with variable clinical signs of piroplasmosis were sampled from Northwest and Northcentral Nigeria and tested by nPCR and cELISA. Blood and serum samples were collected from each horse via jugular venesection. Individually, nPCR or cELISA failed to identify all horses exposed to piroplasms. A combination of species-specific nPCR and the OIE-approved T. equi and B. caballi cELISAs enhanced the detection of horses exposed to parasites. The results also demonstrated horses showing abnormal hematology were positive for only T. equi, except for one sample that was coinfected with T. equi and T. haneyi. We also identified ticks collected from some of the horses, with Rhipicephalus evertsi evertsi being the most prevalent. This study shows that a larger proportion of horses in the sample set were exposed to T. equi than B. caballi or T. haneyi. Additionally, ticks that have been previously reported as potential vectors for these parasites were found to have infested sampled horses. Further studies are needed to investigate which tick species are competent vectors for Theileria spp. and Babesia caballi in Nigeria.