Serodiagnosis of Babesia equi infection--a comparison of Dot-ELISA, complement fixation test and capillary tube agglutination test

Protein Kinase Inhibitors Arrested the In-Vitro Growth of Theileria equi

INTRODUCTION

Theileria equi is an intra-erythrocytic apicomplexean protozoa that infect equines. Protein kinases (PK), key molecules of the apicomplexean life cycle, have been implicated as significant drug targets. The growth inhibitory efficacy of PK inhibitors against Theileria/Babesia animal parasites have not been documented so far.

METHODS

The present study aimed to carry out in-vitro growth inhibitory efficacy studies of four novel drug molecules-SB239063, PD0332991 isethionate, FR180204 and apigenin, targeting different protein kinases of T. equi. A continuous microaerophilic stationary-phase culture (MASP) system was established for propagation of T. equi parasites. This in-vitro culture technique was used to assess the growth inhibitory effect of protein kinase targeted drug molecules, whereas diminazene aceturate was taken as control drug against T. equi. The inhibitory concentration (IC₅₀) was determined for comparative analysis. The potential cytotoxicity of the drug molecule was also assessed on horse's peripheral blood mononuclear cells (PBMCs) cell line.

RESULTS

SB239063 and diminazene aceturate drugs significantly inhibited (p < 0.05) the in-vitro growth of T. equi parasite at 0.1 µM, 1 µM, 10 µM, 50 µM and 100 µM concentration at ≥ 48 h of incubation period and respective IC₅₀ values were 4.25 µM and 1.23 µM. Furthermore, SB239063 was not cytotoxic to the horse PBMCs and found safer than diminazine aceturate drug. PD0332991 isethionate and FR180204 are extracellular signal-regulated kinase (ERK) inhibitors and significantly (p < 0.05) inhibited T. equi in-vitro growth at higher concentrations (≥ 48 h of incubation period) with respective IC₅₀ value of 10.41 µM and 21.0 µM. Lower concentrations of these two drugs were not effective (p > 0.05) even after 96 h of treatment period. Apigenin (protein kinase-C inhibitor) drug molecule was unsuccessful in inhibiting the T. equi parasite growth completely. After 96 h of in-vitro treatment period, a parasite viability study was performed on drug-treated T. equi parasitized RBCs. These drugs-treated parasitized RBCs were collected and transferred to wells containing fresh culture media (without drug) and naïve host RBCs. Drug-treated RBCs collected from SB239063, PD0332991, diminazene aceturate treatment (1 µM to 100 µM concentration) were unsuccessful in growing/multiplying further. Apigenin drug-treated T. equi parasites were live after 96 h of treatment.

CONCLUSION

It may be concluded that SB239063 was the most effective drug molecule (being lowest in IC₅₀ value) out of the four different protein kinase inhibitors tested in this study. This drug molecule has insignificant cytotoxic activity against horse's PBMCs.

Morphology, epidemiology, and phylogeny of Babesia: An overview

Babesiosis is a tick-borne hemoprotozoan disease of domestic and wild animals. The disease is caused by various species of Babesia and some species of Babesia have also zoonotic significance. The parasite in vertebrate hosts’ remains in erythrocytes and the morphology of Babesia spp. is not uniform in all vertebrate hosts. With the advancement of science, particularly the use of molecular techniques made it easy to study the evolution of parasites and thereby reclassifying Babesia spp. as per their phylogeny and to establish the relation of one isolate of Babesia spp. with isolates throughout the world. An attempt also made in this communication to enlighten the readers regarding relationship of one isolate of Babesia spp. of a particular area to another isolate of Babesia spp. of that area or other parts of the world and phylogenetic classification of Babesia spp. was also discussed. It has been concluded that as the study on Babesia is complex in nature so monitoring of the infection with the use of modern techniques is very much needed to control the infection. Second, more research work on phylogenetic relationship of Babesia spp. isolated from different hosts is needed, particularly in India to know the evolution of Babesia spp. of a particular area, as it has great importance to study the trans boundary diseases of animals.

Seroprevalence and risk factors associated with Babesia caballi and Theileria equi infections in donkeys from Southern Italy

Equine piroplasmosis (EP) has been frequently described in donkeys in subtropical and tropical regions, but published data reflecting large scale surveys are very limited in Europe. The seroprevalence of Babesia caballi and Theileria equi was determined in a donkey population from Campania Region in Southern Italy using a commercial indirect fluorescent antibody test (IFAT), and the risk factors associated with the occurrence of the infection were assessed. Of 203 samples, the overall seroprevalence for EP was 57.1% (116/203), with 35.5% (72/203) for B. caballi and 44.3% (90/203) for T. equi. Co-infection was detected in 46 donkeys (22.6%). The distribution of IFAT antibody titres to B. caballi was: 1:80 (n= 67), 1:160 (n= 2), 1:320 (n= 3); while the distribution of IFAT antibody titres to T. equi was: 1:80 (n= 25), 1:160 (n= 42), 1:320 (n= 12), 1:640 (n= 8), 1:1280 (n= 3). All examined donkeys were asymptomatic, except one adult male (with a titre of 1:640 against T. equi) that showed clinical signs corresponding to the acute stage of EP, reported for the first time in Italy. The unique risk factor associated with a higher B. caballi seroprevalence was the presence of horses in the farms, while risk factors associated with a higher T. equi seroprevalence were poor body condition, presence of ruminants in the farms and milk production. The results indicate a high level of exposure in donkeys living in Southern Italy and suggest that donkeys may be an important reservoir of EP.

Development of EMA-2 recombinant antigen based enzyme-linked immunosorbent assay for seroprevalence studies of Theileria equi infection in Indian equine population

Equine piroplasmosis is a tick-transmitted protozoan disease caused by Theileria equi and/or Babesia caballi. In the present study, we expressed a 53kDa protein from the truncated EMA-2 gene of T. equi (Indian strain) and developed EMA-2ELISA using this expressed protein. This ELISA is able to detect T. equi-specific antibodies in experimentally infected animals as early as 9 days post-infection. The assay developed was validated with the OIE recommended competitive ELISA (cELISA) on 120 serum samples and significant agreement (kappa=0.93) was observed between results of both the ELISAs which indicates suitability of EMA-2ELISA for use in sero-diagnosis. Diagnostic sensitivity and specificity of EMA-2ELISA - as compared with cELISA - were 0.97 and 0.96, respectively. Analysis of 5651 equine serum samples - collected during 2007-2012 from 12 states of India representing eight agro-climatic zones - by EMA-2ELISA revealed 32.65% seroprevalence of T. equi in India. In conclusion, the EMA-2ELISA developed using the T. equi EMA-2 recombinant protein as antigen for detecting T. equi-specific antibodies has good diagnostic potential for sero-epidemiological surveys.

Infectivity rate and transmission potential of Hyalomma anatolicum anatolicum ticks for Babesia equi infection

The infectivity rate of Babesia equi in the salivary glands of Hyalomma anatolicum anatolicum was assessed. The hungry nymphs were fed on a donkey experimentally infected with B. equi. The engorged dropped-off nymphs were collected at different levels of parasitaemia and kept in BOD incubator. After ecdysis, the hungry adults were prefed on rabbits for different time intervals, thereafter the salivary glands were dissected out and acini were examined after methyl green pyronin (MGP) staining. A total of 134 male and 139 female ticks were dissected out. Average infected acini per tick were found to be significantly higher (p<0.05) in male as compared to the female ticks. Further, maximum infected acini in both male and female ticks were found at 24h of prefeeding on rabbits and overall infected acini per tick increased with rise in parasitaemia. The release of infected ticks on susceptible donkeys resulted in development of clinical babesiosis.

In-vivo therapeutic efficacy trial with artemisinin derivative, buparvaquone and imidocarb dipropionate against Babesia equi infection in donkeys

The therapeutic efficacy of imidocarb, artesunate, arteether, buparvaquone and arteether+buparvaquone combination was evaluated against Babesia equi of Indian origin in splenectomised donkeys with experimentally induced acute infection. Efficacies of these drugs were tested by administering each drug or drug combination to groups of donkeys (having three donkeys each group). One group of donkey was kept as untreated control for comparing the results. Parasitaemia, haematology (WBC, RBC, PCV, granulocytes and haemoglobin), biochemical parameters (SAST, SALT, alkaline phosphatase, albumin/globulin ratio) were monitored at regular intervals. Individually, arteether and buparvaquone were found to have no parasite clearing efficacy and the treated animals died within 5-6 days after showing high parasitaemia and clinical symptoms of the disease. However, artesunate treated animals were able to restrict the parasite multiplication but only during the treatment period. Animals treated with imidocarb and arteether+buparvaquone combination were able to clear the parasite from the blood circulation after 2-5 days post-treatment (PT). After 55-58 days PT, recrudescence of B. equi parasite was observed in both these groups and a mean survival period of 66 days and 69 days, respectively, was recorded in these groups. Results of haemato-biochemical parameters had shown that imidocarb had deleterious effect on the liver function while on the other hand arteether+buparvaquone combination was found to be safe. This limited study indicates that arteether+buparvaquone combination could be a better choice than imidocarb for treating B. equi infection, but further trials are required in detail.

Vaccination of donkeys against Babesia equi using killed merozoite immunogen

Protective efficacy of a killed Babesia equi immunogen was assessed in donkeys. The immunogen was prepared from B. equi infected blood so as to contain lysate of 2 x 10(10) parasitised erythrocytes per dose. The immunogen was mixed with an adjuvant Quil A (3mg) and inoculated into four susceptible donkeys (group I). A booster inoculation was given after 21 days of first inoculation followed by challenge with fresh infected blood containing 1x10(11) parasitised erythrocytes 14 days later. Two groups of two donkey each were included as adjuvant only control (group II) and uninoculated control (group III), respectively. After challenge, donkeys were observed for a period of 4 weeks. The immunised donkeys (group I) showed significantly high (P<0.05%) enzyme linked immunosorbant assay (ELISA) antibody titres and significantly high (P<0.05%) stimulation indices (SI) in lymphocyte proliferation assay (LPA) than that of groups II and III donkeys from day 14 PI and day 7 PI onwards, respectively. All the immunised donkeys withstood lethal challenge, whereas, control donkeys died within 10 days post-challenge (PC). Parasitaemia rose to mean maximum 8.0+/-6.0% for 5-7 days in group I donkeys after challenge, whereas, it rose to 55.5% in control groups. The percent rise in rectal temperature, total leucocyte count (TLC), fall in haemoglobin (Hb) was less severe in immunised group as compared to the control groups. Two immunised-challenged donkeys were splenectomised recovery. No parasites appeared in the blood during the observation period following splenectomy 4-week. Three times increase in skin-fold thickness at 24h of intradermal inoculation prior to challenge in group I donkeys was observed, thus, indicating a good in vivo cell mediated immunity. It can be concluded that the B. equi immunogen along with adjuvant Quil A, used in the present study, was optimum to elicit a strong immune response against B. equi in experimental donkeys.

Detection of Babesia equi (Laveran, 1901) by nested polymerase chain reaction

We describe a nested polymerase chain reaction (PCR) for the detection of Babesia equi in equine infected erythrocytes using oligonucleotides designed on the published sequence of a B. equi merozoite antigen gene (ema-1). A 102bp DNA fragment is specifically amplified from B. equi but not from Babesia caballi, Babesia bovis or Babesia bigemina DNA. In a mock infection we were able to detect down to six infected cells in 10(8) equine erythrocytes or to detect the parasite in blood with an equivalent parasitemia of 0.000006%. Furthermore, gene polymorphism was found by performing a PCR-RFLP (PCR combined with restriction fragment length polymorphism) on both the 102bp and the entire ema-1 gene DNA amplified from two B. equi isolates, Florida (USA) and Pelotas (Southern Brazil) isolates. The polymorphism was confirmed by sequencing the entire ema-1 gene from the B. equi isolate Pelotas. Our results demonstrate that the ema-1 based nested PCR is a valuable technique for routine detection of B. equi in chronically infected horses. It may be used for epidemiological and phylogenetic studies of the parasite as well as monitoring B. equi infected horses in chemotherapeutic trials.

Molecular detection of Babesia equi and Babesia caballi in horse blood by PCR amplification of part of the 16S rRNA gene

Babesia equi and Babesia caballi are tick-borne haemoparasites that may cause babesiosis of Equidae. In southern Europe B. equi is enzootic and infections may occur asymptomatically and more frequently than those due to B. caballi. Complement fixation test (CFT) is the official serological test for the diagnosis of equine babesiosis, but it has low sensitivity during early and latent stages of the disease. With the aim of developing more sensitive and rapid direct diagnostic alternatives, PCR systems that amplified DNA targets of 664 or 659 bp regions of the 16S rRNA genes were designed and demonstrated to specifically detect the genomes of B. equi and B. caballi, respectively. An approximated parasitaemia of 0.000083% was detected by the PCR system for B. equi compared with reported limits of 0.001% for microscopic examination of stained blood smears, and up to 0.00025% for DNA probes. Although the sensitivity of the PCR system for B. caballi could not be estimated, samples with microscopically undetectable parasitaemia as well as those with 0.017% parasitised red blood cells were detected. DNA extracts of blood collected with EDTA as an anticoagulant from 23 horses from Portugal were tested with both PCR systems. Of these samples, 22 were positive for B. equi and 8 were positive for B. caballi with PCR tests and intraerythrocytic parasites were seen in all samples. Antibodies against both parasites were not detected by CFT in several cases, but in these cases the presence of either or both parasites was apparent by PCR tests. The PCR systems may be useful in the diagnosis of equine babesiosis covering a wider range of clinical disease, as useful adjuncts to serological, microscopic, and cultural methods, especially for the import and export testing of horses.