Risk of a rift valley fever epidemic at the haj in Mecca, Saudi Arabia.

Rift Valley fever (RVF) is a zoonotic disease that affects both humans and domestic animals. In humans, it can cause a fatal haemorrhagic fever disease. When domestic animals such as sheep, goats, camels and cattle are infected, the infection may or may not be accompanied by clinical signs of disease. Both sub-clinical and clinically affected animals present a hazard as a source of infection for humans. The risk of infection is greatest at the time of killing, when aerosols of infected blood may be generated, particularly by traditional sacrificial slaughtering practices. Every year some 10 million to 15 million small ruminants may be slaughtered during the religious festivals at Mecca. Some of these animals come from the Arabian Peninsula itself, but most are imported across the Red Sea, from countries in East Africa and the Horn of Africa, where RVF is known to be enzootic and can be greatly amplified during periods of epizootic virus activity. These animals may be transported to and arrive in Mecca within the incubation period for the disease. Rift Valley fever is also known to occur in the tihama zones of both Saudi Arabia and Yemen.