PCR diagnosis of tick-borne pathogens in Maharashtra state, India indicates fitness cost associated with carrier infections is greater for crossbreed than native cattle breeds

Abstract

Tick-borne pathogens (TBP) are responsible for significant economic losses to cattle production, globally. This is particularly true in countries like India where TBP constrain rearing of high yielding Bos taurus, as they show susceptibility to acute tick borne disease (TBD), most notably tropical theileriosis caused by Theileria annulata. This has led to a programme of cross breeding Bos taurus (Holstein-Friesian or Jersey) with native Bos indicus (numerous) breeds to generate cattle that are more resistant to disease. However, the cost to fitness of subclinical carrier infection in crossbreeds relative to native breeds is unknown, but could represent a significant hidden economic cost. In this study, a total of 1052 bovine blood samples, together with associated data on host type, sex and body score, were collected from apparently healthy animals in four different agro-climatic zones of Maharashtra state. Samples were screened by PCR for detection of five major TBPs: T. annulata, T. orientalis, B. bigemina, B. bovis and Anaplasma spp.. The results demonstrated that single and co-infection with TBP are common, and although differences in pathogen spp. prevalence across the climatic zones were detected, simplistic regression models predicted that host type, sex and location are all likely to impact on prevalence of TBP. In order to remove issues with autocorrelation between variables, a subset of the dataset was modelled to assess any impact of TBP infection on body score of crossbreed versus native breed cattle (breed type). The model showed significant association between infection with TBP (particularly apicomplexan parasites) and poorer body condition for crossbreed animals. These findings indicate potential cost of TBP carrier infection on crossbreed productivity. Thus, there is a case for development of strategies for targeted breeding to combine productivity traits with disease resistance, or to prevent transmission of TBP in India for economic benefit.

Prevalence of Tick-borne Pathogens in Co-grazed Dairy Bovines Differs by Region and Host-type in Tamil Nadu, India

“…A PCR assay targeting the 18s rRNA gene was utilised for amplification of 5 different TBP based on conditions and primers, as described previously [6]. Specificity of the PCR was tested by direct sequencing two PCR products, and BLAST analysis of the amplicons.…”

“…Less specific primers were designed to amplify Anaplasma; +ve samples were scored as Anaplasma spp. for the results from this assay [6]. PCR amplification was performed in a final volume of 25 µl, with each reaction containing 4 µl of DNA template, 4.5 µl of nuclease free water, 12.5 µl of 1.5 mM Mgcl 2 (Taq 2X Master mix, Red Ampliqon) and 2 µl of each primer at 10 pmol.…”

“…Use of a GLMM approach allowed us to flexibly model nonnormally distributed response variables, accounting for fixed factors (Sex, Age Class, Host type and Tick scores), while including geographic location as a random effect (Block) to control for non-independence of hosts from the same location of origin [14]. Two models containing Citation: Ponnudurai G, Larcombe S, Velusamy R, Rani N, Kolte SW, et al (2017) Prevalence of Tick-borne Pathogens in Co-grazed Dairy different response variables were constructed: the prevalence of Theileria annulata as a binary distributed response, and the prevalence of Anaplasma spp. as a binary distributed response.…”

“…Specific amplification was validated by sequencing in a parallel study that used the same primers and PCR conditions: the top BLAST hits for sequenced PCR products matched the intended target [6]. Results of the PCR assay for T. annulata were initially correlated with location and host type: 76.2% , 68.0% and 26.4% of crossbred cattle, native cattle and buffaloes, respectively from the North Western region were infected, and 67.1%, 54.5% and 4.0% in crossbred cattle, native cattle and buffaloes respectively from the Cauvery delta region.…”

“…Economic loss due to tropical theileriosis in India is estimated to be US$800 million [4] but this is likely to be an underestimate as substantial losses from subclicinal carrier infection are rarely captured [5]. A recent survey carried out in Maharashtra state, India showed that the fitness cost to apparently healthy animals with subclinical infection of tick-borne haemoparasites (Theileria and Babesia) were more pronounced in crossbreed than in native breed cattle [6]. Such losses are of importance in India, where a growing population relies on dairy products as a primary source of protein [1].…”