Prevalence and associated risk factors of Bluetongue virus in Punjab and Balochistan

Abstract

Bluetongue (BT) is a vector-borne disease of immense economic importance for small and large ruminants. Despite frequent disease reports from neighboring countries, a little is known about current disease status and prevalent serotypes in Pakistan. We screened a total of 1,312 healthy animals (sheep= 326, goat= 476, cattle= 234, buffalo= 276) from Punjab and 876 from clinically healthy sheep (475) and goats (401) from Balochistan for the detection of group-specific antibodies and serotype-specific genome for BT virus through competitive ELISA and real-time PCR, respectively. An overall prevalence of group-specific VP7 antibodies [28.81% (n= 378/1312, 95% CI=26.4 – 31.4)] was observed in Punjab. The prevalence was higher in goats [40.75% (n=194/476, 95% CI=36.4 – 45.3)] followed by buffalo [29.34% (n=81/276, 95% CI=24.3 – 34.9)], sheep [18.40% (n= 60/326, 95% CI=14.5 – 22.9)] and cattle [17.94% (n= 42/234, 95% CI= 13.56 – 23.4)]. The odds of seropositivity were more in buffalo of Nili breed (OR= 2.06, 95% CI= 1.19-3.58) as well as those found with a presence of vector (OR= 2.04, 95% CI= 1.16-3.59). Buffalo and cattle with history of abortion [(OR= 3.95, 95% CI= 1.33-11.69) and (OR= 5.89, 95% CI= 1.80-19.27) respectively] were much likely to be infected with the disease. Serotype 8 was detected in all animal species while, serotypes 4 and 6 were detected in sheep, 2, 6 and 11 in goat, and 2 and 16 in buffalo. The study concludes a much frequent exposure of different serotypes of Bluetongue virus (BTV) in small and large ruminants and indicates its expansion to enzootic range worldwide.In Balochistan, none of the study herds (n = 97) were seronegative for BTV, and at the individual level, the overall prevalence of BTV seroconversion was 47.26% (n = 414/876, 95% CI=43.92-50.63%). A higher percentage of goats (50.87%, 95% CI = 45.99-55.73%) were seropositive for anti-VP7 immunoglobulins (IgG) than sheep (44.21%, 95% CI= 39.81-48.70%). Odds of seroconversion for goats were associated with breed-type (χ2 = 16.84, p = 0.01), parity (χ2 = 23.66, p = 0.00) and presence of vector (χ2 = 2.63, p = 0.10), whereas for sheep, it was associated with breed-type (χ2 = 13.80, p = 0.01) and parity (χ2 = 53.40, p = 0.00). The presence of vector was also observed to be a risk factor in goat. Serotype 8 was the most prevalent (26.82%, 95% CI=14.75-43.21%) followed by an equal prevalence of serotypes 2 and 9 (7.31%, 95% CI= 1.91-21.01%). To the best of our knowledge, this is the first study conducted in Balochistan province and the results indicate that there is a necessity to initiate intervention strategies to control BT disease burden not only in this region of Pakistan but also in adjacent areas of the neighboring countries, Iran and Afghanistan.