Climate change and the emergence of Rift Valley fever virus: a pathological and environmental study of sheep jaundice in Egyptian slaughterhouses.

Abstract

Background: The emergence of Rift Valley Fever Virus (RVFV) and its link to sheep jaundice in Egypt highlights the growing impact of climate change on the epidemiology of vector-borne diseases. Shifting climatic patterns, such as rising temperatures and altered rainfall, have expanded mosquito habitats, enhancing RVFV transmission risks. These environmental shifts create ideal breeding conditions for the mosquitoes, increasing virus's transmission risk to both livestock and humans. Jaundice, a severe symptom resulting from RVFV infection, not only threatens livestock health but also poses significant economic challenges for farmers who rely heavily on their animals.

Method: A descriptive case series study was performed to assess the impact of climate change on the total condemned sheep due to jaundice at Al-Basatin automated slaughterhouse. A total of 100 animals were examined from June to December 2024. Nineteen cases of jaundice were investigated to determine the cause. Gross examinations, histopathology, and immunohistochemical studies of caspase-3 and tumor necrosis factor alpha (TNFα), were conducted on various organs of jaundice affected cases. Frozen tissue samples were processed for molecular detection of RVFV, and determination of gene expression of heat shock 70KDa protein 1 A (HSP70) and bradykinin receptor B1 (BDKRB1). Malondialdehyde (MDA) and reduced glutathione (GSH), were analyzed to evaluate oxidative stress.

Results: Gross examination of liver, kidneys, heart, and lungs of 19 jaundice affected sheep showed various lesions. Histopathological changes in 16 cases were indicative of RVF infection, while 3 cases were of unknown jaundice cause. RVF infection elevated immunoexpression of caspase-3 and TNFα. The presence of RVFV was confirmed in liver and kidney tissues. A significant correlation (p < 0.01) was observed between the occurrence of jaundice in sheep and extreme (THI > 25.6) to severe heat stress (HS) (THI = 23.2 to < 25.6). During the hot summer months, there was an increase in MDA, HSP70, and BDKRB1, and reduced GSH in liver and kidney.

Conclusion: This study demonstrates a direct connection between climate change and the occurrence of RFV infection and jaundice in sheep. This relationship is likely linked to increased oxidative stress biomarkers in sheep and a weakened antioxidant defense system. These factors contribute to HS, triggering histopathological changes across all vital organs.