The Burden of Disease and Other Causes of Morbidity and Mortality in Backyard Chickens in Low-Income and Middle-Income Countries

Abstract

Backyard chicken farms are the predominant poultry production system in low-income and middle-income countries (LMICs), being considered subsistence farming as they contribute to household food security and nutrition through the production of meat, eggs, and manure for crop fertilization. Backyard chickens do not achieve their full production potential because of their exposure to diverse risks. Their living environment and management practices, such as low biosecurity, facilitate the incursion of pathogens, leading to an increase of morbidity and premature deaths.

The aim of this thesis is to quantify the productivity and economic impacts of the main causes of morbidity and mortality in backyard chickens in LMICs, generate an understanding of the availability of prevalence data and fill knowledge gaps on leading diseases in low-resource settings.

A general introduction (Chapter 1) sets the scene for the subject investigated in this thesis. It defines what backyard chicken farms are, conceptualises the economic impact of livestock diseases, introduces the Global Burden of Animal Diseases (GBADs) programme, describes the research objectives, and justifies the epidemiological approaches used in this thesis. In the first study (Chapter 2), a systematic literature review and meta-analysis, we estimated the productivity and economic impact of diseases and other causes of morbidity and mortality. Infectious causes, namely viral and bacterial diseases and non-infectious causes, predation, and cachexia, are the leading causes of mortality recorded per production cycle that also account for the highest economic losses in backyard chickens in LMICs. A limited number of studies on productivity (meat and egg) impacts were found, highlighting the need for research in this area.

In the second study (Chapter 3), we described a dataset on disease prevalence that was gathered during the screening process of the systematic literature review (Chapter 2). We did not find prevalence and seroprevalence data on backyard chicken diseases in 56.9% of LMICs, showing a potential knowledge gap. In countries where we found data, 71.0% of the viral and bacterial prevalence estimates corresponded to diseases notifiable to the World Organisation for Animal Health (WOAH), highlighting a tendency to measure the prevalence of these diseases, which are relevant to international trade.

In the third study (Chapter 4), we predicted coccidiosis prevalence in backyard chickens in the countries and regions of the Horn of Africa, using climatic factors, to bridge the data gap. Results show a predicted prevalence in the Horn of Africa of 0.21 (95% CI: 0.15-0.29). Significant differences were found between the countries with the highest prevalence, namely, Ethiopia, the Republic of South Sudan and Kenya with Djibouti, the country with the lowest prevalence. Confidence intervals overlap between the rest of the countries and those previously mentioned, suggesting no significant difference.

Chapter 5 synthetises and contextualises the main findings of this thesis to the research field and to the GBADs programme, present limitations, future perspectives and overarching conclusions.