Development of a duplex real-time PCR assay for simultaneous detection and differentiation of Theileria equi and Babesia caballi

Quantitative detection of Theileria haneyi in South African horses

Theileria haneyi is an apicomplexan parasite closely related to Theileria equi, a known causative agent of equine piroplasmosis. The molecular distinction between these parasites relies on a nested polymerase chain reaction (PCR) assay, which has been reported to be unreliable. A recently reported indirect ELISA based on equi merozoite antigen 11 (Thema-11) of T. haneyi can detect geographically diverse T. haneyi strains. Since the ema-11 gene is exclusive to T. haneyi, it was chosen as the target for developing a TaqMan minor groove binder (MGB™) quantitative real-time PCR (qPCR). Published T. haneyi ema-11 gene sequences were used to design primers to amplify the ema-11 gene, and ema-11 amplicons from South African samples were cloned and sequenced. An alignment of the South African ema-11 gene sequences with published T. haneyi ema-11 gene sequences enabled the identification of a conserved region for the design of the qPCR assay. The T. haneyi ema-11 (Thema-11) qPCR assay was efficient, specific, and sensitive in detecting T. haneyi ema-11. The detection limit was determined to be 1.169 × 10-3 % parasitized erythrocytes. The performance of the Thema-11 qPCR assay was evaluated together with a T. equi ema-1-specific qPCR assay. Theileria haneyi was detected in 67.6 % of the South African field samples screened, while the occurrence of T. equi based on the quantitative amplification of the ema-1 gene was higher (91.8 %). Our results suggest that combined, the Thema-11 and T. equi ema-1 qPCR assays could detect and differentiate between T. haneyi and T. equi infections.

Prevalence and molecular epidemiology of the novel equine parasite Theileria haneyi in China

BACKGROUND

Equine piroplasmosis (EP), caused by Theileria equi (T. equi) and Babesia caballi (B. caballi), is a tick-borne disease with significant economic impacts on the equine industry. Theileria haneyi (T. haneyi), a newly identified pathogen of EP, is globally distributed but has not been reported in China, where its epidemiological patterns remain undefined.

OBJECTIVES

To develop diagnostic techniques for T. haneyi and to assess its prevalence and risk factors in China.

STUDY DESIGN

Assay development and cross sectional survey.

METHODS

A nested PCR (nPCR) nucleic acid diagnostic technique targeting the chromosome 1 single-copy (chr1sco) open reading frame (ORF) was developed. This method was applied to 1318 equine nucleic acid samples. Additionally, an iELISA serological diagnostic method was established based on the EMA11 gene. This method was utilised in a cross-sectional analysis of 2627 equine samples. Logistic regression analysis was performed to identify significant risk factors.

RESULTS

The nPCR assay showed an 11.76% positive detection rate, while iELISA indicated a 16.41% seroprevalence. Both assays were successfully applied for the epidemiological investigation of T. haneyi. Logistic regression analysis identified host species, age, altitude, soil type, and forest and grassland coverage as the main risk factors influencing seropositivity. Phylogenetic analysis of 18S rRNA from 29 positive samples confirmed the presence of T. haneyi in China.

MAIN LIMITATIONS

Data on clinical signs were not collected. The logistic regression model's performance metrics were not calculated.

CONCLUSIONS

This study provides the first evidence of T. haneyi infection in China and establishes a scientific basis for understanding its prevalence and geographical distribution.

Molecular Investigations of Babesia caballi from Clinically Healthy Horses in Southwestern Romania

Babesia caballi is a tick-borne hemoparasite that causes equine piroplasmosis. It has a significant economic impact, decreasing performance and affecting animal welfare. This study aimed to identify B. caballi DNA in the blood of horses from households in the southwestern and western regions of Romania. We included 310 animals, from which blood was collected via EDTA. To test the samples for the B. caballi parasite genome, we used real-time PCR and conventional PCR. The prevalence of B. caballi was 5.81% (18/310) in apparently healthy horses, suggesting that this parasite is enzootic in the regions studied, although veterinarians did not indicate any symptoms resembling clinical babesiosis. In Romania, there are insufficient epidemiologic data on equine babesiosis, and the results of the present study suggest the need for further investigations into the dynamics of transmission and to identify potential prevention and control strategies.

Molecular and immunological studies on Theileria equi and its vector in Egypt

Equine piroplasmosis is not fully understood regarding pathogenicity, prophylaxis, host immune response expression, and specific vectors. Accurately identifying the parasite vector is crucial for developing an effective control plan for a particular infection. This study focused on morphologically identifying two Hyalomma species (H. anatolicum and H. marginatum) and one Rhipicephalus annulatus (R. annulatus) at the species level. The identification process was followed by phylogenetic analysis using the neighbor-joining method based on the cytochrome oxidase subunit 1 (COXI) gene as a specific vector for Theileria equi (T. equi) in horses. T. equi was diagnosed morphologically and molecularly from infected blood samples and crushed tick species using conventional PCR. Subsequently, phylogenetic analysis based on the amplification of the 18 S rRNA gene was conducted. The obtained sequence data were evaluated and registered in GenBank under accession numbers OR064161, OR067911, OR187727, and OR068139, representing the three tick species and the isolated T. equi, respectively. The study demonstrated that T. equi infection leads to immune system suppression by significantly increasing the levels of oxidative stress markers (CAT, GPx, MDA, and SOD) (P ≤ 0.0001), with this elevation being directly proportional to parasitemia levels in infected blood cells. Furthermore, a correlation was observed between parasitemia levels and the expression of immune response infection genes (IFN-gamma, TGF-β1, and IL-1β cytokines) in infected horses compared to non-infected equine. Common macroscopic symptoms indicating T. equi infection in horses include intermittent fever, enlarged lymph nodes (LN), and tick infestation.

The first study of the prevalence and genetic diversity of Theileria equi and Babesia caballi in horses in Russia

Equine piroplasmosis (EP) is a global worldwide infection, which can lead to the death of animals. Despite the causative agents of EP being well studied, there are no data on the distribution and genetic characteristics of EP agents in any region of Russia. In this study, blood samples from 750 horses from Novosibirsk province, Irkutsk province, and Altai region of Russian Siberia were examined for the presence of EP agents. Theileria equi and Babesia caballi were detected in all examined regions, with mean prevalence rates of 60.4% and 7.2%, respectively. The identified pathogens were genetically characterized by the 18S rRNA gene. The determined T. equi sequences were highly conserved and belonged to genotypes A and E, with genotype E being found in 88.6% of genotyped samples. In contrast to T. equi, B. caballi sequences were genetically diverse. Seven sequence variants of B. caballi were identified, and only two of them matched known sequences from the GenBank database. The determined B. caballi sequences belonged to four distinct branches within genotype A. Mixed infections with several variants of B. caballi or with T. equi and B. caballi were common. The conducted phylogenetic analysis based on all available B. caballi sequences of the 18S rRNA gene (> 900 bp) from GenBank and from this study first demonstrated the presence of five monophyletic clusters within genotype A and three clusters within genotype B. Thus, the genetic study of B. caballi from Siberia has significantly expanded the data on the genetic diversity of this pathogen.

Investigation of Babesia spp. and Theileria spp. in ticks from Western China and identification of a novel genotype of Babesia caballi

Babesia spp. and Theileria spp. are tick-borne protozoan parasites with veterinary importance. In China, epidemiological and genetic investigations on many Babesia and Theileria species were still absent in many areas and many tick species. From Aug 2021 to May 2023, 645 ticks were collected from the body surface of domestic animals (camels, goats, sheep, and cattle) using tweezers in seven counties in three provinces including Xinjiang (Qitai, Mulei, Hutubi, and Shihezi counties), Chongqing (Youyang and Yunyang counties), and Qinghai (Huangzhong county). Three tick species were morphologically and molecularly identified (334 Hyalomma asiaticum from Xinjiang, 245 Rhipicephalus microplus from Chongqing, and 66 Haemaphysalis qinghaiensis from Qinghai). A total of three Babesia species and two Theileria species were detected targeting the 18S gene. The COI and cytb sequences were also recovered from Babesia strains for further identification. In R. microplus from Chongqing, Babesia bigemina, the agent of bovine babesiosis, was detected. Notably, in H. asiaticum ticks from Xinjiang, a putative novel genotype of Babesia caballi was identified (0.90%, 3/334), whose COI and cytb genes have as low as 85.82% and 90.64-90.91% nucleotide identities to currently available sequences. It is noteworthy whether the sequence differences of its cytb contribute to the drug resistance of this variant due to the involvement of cytb in the drug resistance of Babesia. In addition, Theileria orientalis and Theileria annulata were detected in R. microplus from Chongqing (12.20%, 31/245) and H. asiaticum from Xinjiang (1.50%, 5/334), respectively. These results suggest that these protozoan parasites may be circulating in domestic animals in these areas. The pathogenicity of the novel genotype of B. caballi also warrants further investigation.

Molecular genotyping of Babesia caballi

Babesia caballi is an intra-erythrocytic parasite causing equine piroplasmosis. Three B. caballi genotypes (A, B, and C) have been identified based on the 18 S rRNA and rhoptry-associated protein (rap-1) gene sequences. These variant parasite genotypes compromise the diagnostic utility of the WOAH-recommended serological assays in declaring horses free of equine piroplasmosis. Although a gene encoding a spherical body protein 4 (sbp4) has recently been identified as a potential antigen for the serological detection of B. caballi, the ability of this antigen to detect the different geographical strains has not been determined. The molecular distinction between variant B. caballi genotypes is limited and therefore we developed molecular typing assays for the rapid detection and quantification of distinct parasite genotypes. Field samples were screened for the presence of B. caballi using an established multiplex equine piroplasmosis qPCR assay. In this study, B. caballi genotype A was not detected in any field samples screened. However, phylogenetic analysis of the amplified sbp4 and 18 S rRNA genes confirmed the phylogenetic groupings of the South African isolates into either B. caballi genotypes B or C. A multiple sequence alignment of the sbp4 gene sequences obtained in this study together with the published sbp4 sequences representing B. caballi genotype A, were used to identify conserved regions within the gene to design three primer pairs and three genotype-specific TaqMan minor-groove binder (MGB™) probes. The qPCR assays were shown to be specific and efficient in the detection and differentiation between B. caballi genotypes A, B, and C and could be used as a diagnostic assay to prevent the unintentional spread of variant B. caballi genotypes globally.

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.

Development and evaluation of specific polymerase chain reaction assays for detecting Theileria equi genotypes

BACKGROUND

Theileria equi causes equine piroplasmosis, an economically significant disease that affects horses and other equids worldwide. Based on 18S ribosomal RNA (18S rRNA sequences), T. equi can be classified into five genotypes: A, B, C, D, and E. These genotypes have implications for disease management and control. However, no conventional polymerase chain reaction (PCR) assays are available to differentiate the genotypes of T. equi. To overcome this limitation, we developed and evaluated PCR assays specific for the detection of each T. equi genotype.

METHODS

A pair of forward and reverse primers, specifically targeting the 18S rRNA sequence of each genotype, was designed. The genotype-specific PCR assays were evaluated for their specificity using plasmids containing inserts of the 18S rRNA sequence of each genotype. Subsequently, the assays were tested on 270 T. equi-positive equine blood DNA samples (92 from donkeys in Sri Lanka and 178 from horses in Paraguay). 18S rRNA sequences derived from the PCR amplicons were analyzed phylogenetically.

RESULTS

Each genotype-specific PCR assay accurately targeted the intended genotype, and did not produce any amplicons when 18S rRNA from other T. equi genotypes or genomic DNA of Babesia caballi or uninfected horse blood was used as the template. Previous studies employing PCR sequencing methods identified T. equi genotypes C and D in the Sri Lankan samples, and genotypes A and C in the Paraguayan samples. In contrast, our PCR assay demonstrated exceptional sensitivity by detecting four genotypes (A, C, D, and E) in the Sri Lankan samples and all five genotypes in the Paraguayan samples. All the Sri Lankan samples and 93.3% of the Paraguayan samples tested positive for at least one genotype, further emphasizing the sensitivity of our assays. The PCR assays also had the ability to detect co-infections, where multiple genotypes in various combinations were detected in 90.2% and 22.5% of the Sri Lankan and Paraguayan samples, respectively. Furthermore, the sequences obtained from PCR amplicons clustered in the respective phylogenetic clades for each genotype, validating the specificity of our genotype-specific PCR assays.

CONCLUSIONS

The genotype-specific PCR assays developed in the present study are reliable tools for the differential detection of T. equi genotypes.