Modelling the burden of disease for cattle–A case of ticks and tick-borne diseases in cattle in a rural set-up in South Africa
Authors: Salih Omran , Chitanga Simbarashe , Govinder Keshlan , Mukaratirwa Samson 
Published: October 2023

Background
The study aimed to estimate the burden of ticks and tick-borne diseases (TBDs) among rural cattle-keeping households of the Eastern Cape province of South Africa using Productivity Adjusted Life Years (PALYs). We modified Disability Adjusted Life Year (DALY) equations for humans to PALYs to estimate the societal burden of tick-borne animal diseases. Whilst the World Health Organization has indicated the adaptability of DALYs to assess burden of animal diseases, nothing has been done in this regard. This could be due to several reasons including that the assessment of animal disease burden is often less of a priority compared to human diseases, particularly in low- and middle-income countries where resources may be limited. As a result, less funding and attention may be given to developing and implementing PALYs for animal diseases. Furthermore, technical and conceptual challenges may be associated with applying DALYs equations to animal diseases, such as determining appropriate measures of productivity loss for different types and categories of animals and diseases. This motivated our study, which is focused on modelling the burden of ticks and TBDs in cattle (cows, oxen and bulls) reared in resource-poor settings.

Method
We formulated a PALYs approach for cattle populations by adapting the DALYs approach to assess the burden of ticks and TBDs for cattle populations in 20 villages in the Eastern Cape province of South Africa. PALYs is a measurement used to assess the burden of disease in cattle populations, quantifying the years of life lost due to premature mortality and disability. It encompasses years of life lost due to premature mortality (YLL) and years lost due to disability (YLD) caused by health conditions. PALYs provide a comprehensive perspective on the effective number of years lost due to disability and premature death in cattle populations. The PALYs model involves several parameters that are examined to understand their impact on the model’s behavior. To illustrate this, we used a structured questionnaire to collect data on parameters that feed into PALY equations. We coded and entered data from questionnaires directly into Statistical Package of Social Sciences (IBM SPSS Version 20) and entered the estimated values of PALY parameters to calculate PALYs equations, which were to estimate the societal disease burden of ticks and TBDs in cattle. PALYs calculations were done in three categories; PALYs without discounting and age weighting, PALYs with only discounting, and PALYs with discounting and age weighting in a practical example to study how these parameters influence the outcomes of the PALYs model.

Results
Our results revealed that the years of productivity lost by a cow, bull, and ox that suffered from ticks and TBDs could be estimated at various disability weights. Approximately 26%, 23% and 35% of the productivity years of a cow, ox and bull, respectively, reared by resource-poor livestock owners are lost due to the burden of ticks and TBDs in the Eastern Cape province of South Africa. However, introducing tick control measures reduces the loss to approximately 3%, 2% and 3% of their lifespan productivity, an indication that tick control will save approximately 23%, 21% and 32% of years of the productive life of cows, oxen and bulls, respectively. Therefore, it is evident that using ticks and TBD prevention measures at an early age of cattle will improve cattle productivity and hence the socioeconomic welfare of resource-poor rural farming communities in the Eastern Cape province of South Africa.

Conclusion
The findings generated from the PALYs approach are helpful in projections for the future burden of any livestock disease. They may be used as a basis in policy formulation and decision-making by various stakeholders, and hence a priority in animal health economics. We recommend that a classification of livestock diseases of national economic importance should consider both the societal burden (non-monetary) and economic impact instead of the common practice of only considering the economic (monetary) impact. Adding a societal burden measure to existing economic measures provides a holistic understanding of the impact of a disease on society especially in resource-limited settings where the livestock value goes beyond monetary value.