Rift Valley Fever: First Out of Africa

Combined Saudi/Yemen statistics, as of 16 January 2001: 227 human deaths out of approximately 1850 cases; tens of thousands of animal mortalities
The 2000 outbreak in Saudi Arabia and Yemen marks the first appearance of Rift Valley Fever outside Africa. Noted as a disease in Kenya's Rift Valley as early as the turn of the last century (the causative virus was isolated in 1930), it has been seen at irregular intervals on the continent, particularly after heavy rains that favor mosquito breeding. It showed up in Zimbabwe (February 1999) and western South Africa (January 1999) after the devastating floods in neighboring Mozambique, and in Uganda/Tanzania/Kenya (March 1998) after the El Nino floods in East Africa. The current outbreak, however, comes after a prolonged drought both in the Horn and in East Africa. Another recent outbreak - in Libya in early 1999 - was also not associated with rains.

The question is, of course, how did the virus get out of Africa. And the answer seems to be through animals imported into the Red Sea port of Jizan. Saudi Arabia, on numerous occasions in the past, has banned importation of animals from various African countries experiencing a Rift Valley outbreak. The last ban (prior to the current outbreak) was imposed on several East African countries in early 1998. It was lifted in June 1999. Livestock imports quickly resumed.

A controversy erupted during that summer of 1999 after scientists at the King Saud University said that mosquitoes carrying West Nile Virus were in Saudi Arabia. The Middle East Newsfile reported on July 12 that Dr. Muhammad Al-Sheikh, head of the livestock production department of the university, said 'it is a grave mistake to deny the presence of Rift Valley Fever carrying mosquitoes which pose a great threat and should be dealt with quickly.' Dr. Al-Sheikh quoted a livestock dealer in Riyadh as saying 'Some sheep from Africa have been found to be infected with the disease.'

The Ministry of Agriculture and Water disagreed, saying firmly that there were no WNF virus carrying mosquitoes in the country. The regional office of the UN Food & Agriculture Organization backed up the ministry, saying that all livestock in the country was completely free of the disease, and further that the FAO had a regional plan to protect the Middle East from the threat, and that the plan was similar to the one implemented in Libya six months earlier.

The problem, it appears, lies in the fact that early animal deaths from the disease usually go unnoticed and do not, even when the numbers grow, greatly impress upon agriculture officials their significance as a reportable disease until human cases are diagnosed. Certainly, notifications from both Saudi Arabia and Yemen to the Office International des Epizooties in Paris on Rift Valley Fever in animals (19 September and 21 September, respectively) were not made until there were over 40 human deaths in Saudi Arabia and over 20 in Yemen.

The total number of animal deaths is difficult to ascertain - complicated by deaths in remote areas and greatly increased by wholesale slaughter to control the spread and prevent more human cases. In late September, before the slaughter had begun, the Saudi Minister of Agriculture and Water said the virus had killed almost 11,000 sheep, cows and camels in the Jizan port area alone. At about the same time, Yemen reported 6000 dead animals. It is reasonable to expect total livestock mortalities, including animals that have been destroyed and aborted fetuses, to be in the range of 40,000.

Rift Valley Fever is part of the sand fly fever group(Phleborivus genus, Bunyaviridae family), but the only fever of this group vectored by mosquitoes. It is transmitted from animals to humans, by bite or by exposure to infected animal tissues. It is, however, important to note that while some Western experts claim to have found the reservoir of the virus in wild rodents in the 1970s in Egypt, African scientists contend that the reservoir is not yet known. Thus, there is significant research still pursued.

Initial clinical signs of the disease in animals are not precisely described. It is often the case that the disease is suspected by a confluence of events - spontaneous abortions, human deaths - after animals die 24-36 hours from the first observance of their appetite loss and listlessness. The mortality rate in animals less than a week old is 90%.