Flock Level Economic Loss Due to Peste Des Petits Ruminants Outbreak in Transhumance Sheep and Goat Population in Himachal Pradesh (India)

Peste des Petits ruminants (PPR) is the most important health constraint in goat and sheep rearing in India. Economic losses due to PPR remains significant (Bardhan et al., 2017a) and the disease is targeted for global eradication in 2030 by FAO and OIE (Parida et al., 2015). India is endemic for PPR and the outbreaks occur in all seasons (Muthuchelvan et al., 2015). The Government of India launched a national control program in 2010 leading to substantial reduction of PPR outbreaks in some states (Muthuchelvan et al., 2014).

In the present study, an investigation was carried out on a PPR outbreak in pastoralist sheep and goat populations in the state of Himachal Pradesh (HP). Sheep and goat rearing are the major source of livelihood for the pastoralists in the state. The circulation of PPR virus in this region and its economic consequences are largely unknown. Economic analysis of the disease, given its importance, is needed from the point of view of optimising resource allocation in disease control programmes. As such, this study aimed to estimate the farm-level economic losses due to the disease in the state and carry out a cost-benefit analysis of control programme through vaccination.

A team of experts from the animal disease investigating laboratory, Shimla, HP attended an outbreak of PPR in transhumance sheep and goats at Kara Khanta alpine pastures in August, 2014. There were 3802 sheep and goats of different age groups in and around the pastures of the area. The team inspected six flocks and carried out clinical, post-mortem and epidemiological investigations. Samples including oral and nasal swabs and tissues from morbid animals were collected. Initial antigen screening was carried out at disease investigating laboratory, Shimla and further confirmed at Indian Veterinary Research Institute (IVRI), Mukteswar Campus. The sandwich ELISA, N-gene based RT-PCR, genetic and phylogenetic analysis were conducted (Muthuchelvan et al., 2014).
 
Estimation of losses due to peste des petits ruminants in investigated flocks
 
The incidence rates as obtained during the above diagnostic study were used to compute the total economic loss at the investigated flock level. The total economic losses due to PPR - comprising mortality loss, direct loss in milk yield (in case of goats) and direct loss in wool yield (in case of sheep), losses due to reproductive failure, loss in body weight, the costs of treatment for affected animals and opportunity costs - were worked out as per the framework given by Singh et al., (2014) and Bardhan et al., (2017a).

The losses, as computed, were used to arrive at the per-animal economic loss due to PPR. The-per animal economic loss was calculated separately considering the incidence rates in the unvaccinated flocks and the same in combined (vaccinated + unvaccinated) flocks.

For estimation of economic losses due to PPR, the authors mostly relied on primary data collected through key informant interview. In addition, tiangulation exercise was carried out by holding focussed group discussion with the herders and cross validating the data obtained as such by discussing with local government veterinary officers and also by referring to secondary data published in various official government publications, like Basic Animal Husbandry Statistics (2017) and Livestock Census (2012). Table 1 summarizes the data on epidemiological and economic parameters - as used in this study - to compute the farm level losses due to PPR in HP.



The incidence of PPR in inspected flocks, as obtained in this study, was used to project the total number of cases and deaths in HP by extrapolating on the sheep and goat population in the state. The loss estimated using the above models were based on incidence rate as obtained in the outbreak study carried out in the study area. As such, the incidence rate used is considered to be high. A sensitivity analysis was also carried out, considering lower assumptions regarding rates. Thus, 75% and 50% of the outbreak incidence were considered as moderate and low scenarios, respectively and accordingly the economic losses were worked out for these different scenarios.

Cost-Benefit Analysis of vaccination against PPR
 
The study has assessed the impact of vaccination against PPR by carrying out a cost-benefit analysis and giving the benefit-cost ratio (BCR). The benefits from vaccination were arrived at by adjusting the economic losses - as obtained in this study - with vaccination coverage (%) and vaccine effectiveness (%) as per the formulae given by Govindaraj et al., (2017).
 

Where
B = Benefits due to vaccination
L = HS induced economic loss
VC = Proportion of animals vaccinated
VE = Vaccine effectiveness
n = Different breeds/species, viz. indigenous and crossbred cattle and buffaloes.
 
The vaccine effectiveness of 75% as reported by de Alwis (1978) was considered in the study. The vaccination coverage was based on the number of flocks vaccinated against PPR as obtained during the inspection of infected flocks. The cost of vaccine was considered at Rs. 2 per dose (as per the prevailing market price) and the cost of vaccination was considered as Rs. 5 per dose which included the salaries of veterinary and para-veterinary staff, vehicle and transport cost, cost of surveillance including diagnostics, laboratory equipments, cost of campaign/awareness creation like poster, travel, etc. The total cost of vaccination by summing all the cost components was divided by the targeted small ruminant population to arrive at the per dose vaccination cost.

Incidence rate of PPR in inspected flocks
 
Table 2 presents the prevalence rates of the inspected flocks in the study area. The overall morbidity and mortality rates in goats and sheep were 36.85% and 27.69% and 25.32% and 1.44%, respectively. The case fatality rates were 75.13% in goats and 5.69% in sheep. Analyses of mortality and morbidity rates - based upon vaccination status - revealed that the morbidity rates were higher for un-vaccinated flocks (56% for goats and 38% for sheep) (Table 3). Mortality rates were also higher in case of un-vaccinated flocks (42% for goats and 2% for sheep). No vaccinated animals were observed to be affected by the disease. In a previous study, there was a PPR outbreak in 1994 in a migratory sheep and goats which passed through the Uttarakhand state to Shimla in HP. In that outbreak, the percent morbidity and case fatality rate for sheep were 9.4 and 0, respectively whereas in goats the rates were 33 and 9.4, respectively (Nanda et al., 1996). Mahajan et al., (2013) reported from Jammu region higher prevalence rate of PPR in goats (66.66%) than in sheep (35.71%).

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Out of 6 flocks investigated, only 2 (flock Nos. 5 and 6) were vaccinated against PPRV, however, in flock No. 5, five kids showed clinical signs.  The affected animals were less than six months old and not vaccinated. Balamurugan et al., (2014) had reported that protective level antibody persisted up to 5 months only and suggested for vaccinating the lambs/kids at the age of 4 and 5 months, respectively. Therefore, the possible reason for the infection in 5 kids in the current study could be due to the lack of protective immunity.
 
Flock level economic losses due to PPR in HP
 
Component-wise per-animal losses due to PPR are given in Table 4 and 5, respectively for unvaccinated and combined flocks. The loss per animal was more when the same was calculated based on incidence rates in unvaccinated flocks. The per animal loss was INR 51.90 and INR 11.40 in case of goats and sheep, respectively. Per-animal loss based on incidence rates in combined flocks was INR 29.19 and INR 7.56, respectively in case of goats and sheep. The higher per head mortality loss (INR 33) in goats than that of sheep (INR 1.5) implies the significantly higher fatality in the former species. Lower case fatality ratio in sheep results in higher opportunity costs, which are costs of extra resources that are employed in care of diseased animals (INR 1.29 per head) as compared to the same for goats (INR 0.5).

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Table 6 presents the proportional contribution of different components of the total loss. There were hardly any differences in the shares of different loss components to total losses, whether computed on the basis of unvaccinated or combined flocks. In case of goats, the greatest share (around 65%) of the total economic losses due to PPR were made up of mortalities, followed by losses due to reproductive failure (23%), direct loss in body weight (6%) and treatment cost (5%). In case of sheep, mortality losses accounted for a smaller share (14%) of total losses. The major component of losses for sheep was direct body weight losses (52%).

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The study projected losses due to PPR incidence in small ruminant population at the state level. The estimation of state-level losses was carried out pertaining to three scenarios, viz. outbreak incidence as observed in this study and 75% and 50% of outbreak incidence. Under high incidence scenario, the total loss due to PPR in HP was US$ 35.64 million with goats accounting for the overwhelming share of loss (US$ 29.54 million). Under moderate and low incidence rate assumptions, the total losses were estimated at US$ 26.73 million and US$ 18.07 million, respectively. The loss estimates as reported in published literature ranged between US$ 0.003 to 14.6 per head (Opasina and Putt 1985; Thombare and Sinha 2009; Abubakar and Munir 2014). 
 
Cost-Benefit Analysis of PPR control through vaccination
 
The BCR calculated was well over unity for both sheep and goats under all the scenarios, viz. high, moderate and low incidence rates (Table 7), thus indicating that the benefits of vaccination outweigh the associated costs. The BCR ranged between 43:1 to 198:1, depending upon level of incidence rate assumptions and species. The BCR for all levels of incidence rates assumptions were higher for goats than sheep. This is on account of greater prevalence of the disease in goats. The BCR as calculated in this study are in line with Bardhan et al., (2017b) who had reported a BCR of 123:1 for PPR control through vaccination using an economic surplus model.

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There can be variations in many of the assumptions while calculating the returns to PPR control programme. In this context, sensitivity analysis was carried out to ascertain the effect of changes in two of the baseline assumptions. In the first scenario it was assumed that the vaccine has lower efficacy (50%) as compared to the baseline assumption. Given this pessimistic scenario, BCR decreased significantly (Fig 1). In the second scenario, accommodating for increase in vaccination cost by 50% the BCR also declined significantly (Fig 2).

The outbreak of PPRV in transhumance population is a significant threat to the small ruminant animal husbandry as these are migratory in nature. The endemic nature of PPR in India poses significant threat to both the livestock sector and the agriculture sector as a whole. The economic feasibility criteria of vaccination against the disease, as estimated in this study suggest sustaining and intensifying mass prophylactic vaccination to curtail mortality associated with PPR.

The authors acknowledge the support given by Dr. R.K. Singh, Director, ICAR-India Veterinary Research Institute in carrying out the study

None of the authors have any competing interest.