World Health Organization

Emerging and other Communicable Diseases (EMC)

28 January 1998 - revised 28 January

Rift Valley fever and haemorrhagic disease in Kenya and Somalia

Although Rift Valley fever has been confirmed in the current outbreak affecting humans and livestock in Kenya and Somalia, it is evident that other causes have contributed to the high rate of haemorrhagic symptoms and deaths among both humans and animals. Laboratory investigations at the WHO Collaborating Centres at Kenya Medical Research Institute in Nairobi, National Institute for Virology in Johannesburg and at Centers for Disease Control and Prevention in Atlanta have tested specimens from Kenya and Somalia for a wide range of infectious agents but so far the only clear diagnosis is RVF which has been confirmed by virus isolation or implicated through the demonstration of specific IgM antibodies in 30-40% of samples from humans that have been tested.

Preliminary epidemiological studies have shown all areas in Kenya where the RVF infections have occurred in previous years and have recently had heavy rainfall are most likely to have virus ciruclating in both animals and humans. Infections began in November-December 1997. The disease is widespread but presenting with typical RVF symptoms which are in general mild in humans but causing abortions in sheep, goats and camels. Animal vaccination, which would be the most efficient control measure for RVF, is not considered feasible under the current conditions in the affected areas.

Severe haemorrhagic disease is not common for RVF and the absence of RVF virus antibody in about two-third of viral haemorrhagic fever cases tested in the laboratory is a further indication that another infectious or toxic agent is involved. Contrary to the RVF outbreak, the severe cases of haemorrhagic illness have occurred in localized clusters. Unfortunately, these clusters have been reported in remote flooded areas in the north-east near the border with Somalia which are very difficult to reach. WHO and the Task Force in Nairobi are now establishing a base in Garissa for further investigations of the cases of haemorrhagic fever. The international team coordinated by WHO will include members from Epiet, Paris, Epicentre of Médecins Sans Frontières, the National Institute for Virology in Johannesburg, Centers for Disease Control and Prevention and the United States Army. The team will be equipped with a locally rented helicopter to access areas otherwise difficult to reach. The establishment of the team has been made possible thanks to financial support of WHO and the Department for International Development, United Kingdom. Additional funds are being solicited from donors to support an intensive one-month investigation that will begin within the next week.

 

Rift Valley Fever in Kenya and Somalia

Press Release WHO/13 - 26 January 1998

RIFT VALLEY FEVER WIDELY DISTRIBUTED IN KENYA AND SOMALIA

Rift Valley Fever (RVF) is widely distributed in Kenya and Somalia, primarily in animals but also in humans, World Health Organization (WHO) officials investigating the disease outbreak in the two countries say. The estimated number of deaths in Kenya is now 350-400. These deaths are concentrated in Kenya's Northeastern Province and in southern Somalia, where after a critical review of the data from Somalia, a revised count indicates that 80 deaths are suspected to be due to haemorrhagic fever.

RVF is widely distributed throughout Kenya and Somalia, a pattern expected as virus-infected eggs of floodwater breeding mosquitoes hatch from many endemic sites. With the heavy rainfall in East Africa during November, December and January, emergence of RVF can be expected from areas that have had infections in previous years. Health and veterinary officials in neighbouring countries affected by the heavy rains have been alerted to increase their vigilance for reports of disease.

A Task Force consisting of representatives from the Kenyan ministries of health and agriculture, international organizations and nongovernmental organizations involved in fighting the outbreak has been established. WHO, secretariat of the Task Force, has implemented a surveillance system for haemorrhagic fevers in Kenya and Somalia. Specimens from both humans and animals are being collected and referred to the African Medical Research Foundation (AMREF) and the Kenya Medical Research Institute (KEMRI) in Nairobi for testing.

In addition, the secretariat is regularly receiving reports about suspected cases. A Rumour List containing this information has been established and is the basis for follow-up investigation. Response teams comprising health and veterinary staff have been organized and are travelling to sites where cases are reported.

Representatives from the Kenyan Ministries of Health and Agriculture, the WHO offices in Geneva, Kenya and Somalia, the Food and Agriculture Organization, the World Food Programme, the International Federation of Red Cross and Red Crescent Societies, Médecins Sans Frontières, and a coordinator for nongovernmental organizations in Somalia have attended meetings of the Coordinating Group of the Task Force. Reports were presented by team members, including Ministry of Health officials, who had recently travelled to affected areas, including Garissa in the Northeastern Province. The vast majority of the deaths are in this remote province and in Southern Somalia.

Epidemiologic analysis of the available information indicates that while RVF infections are occurring in the inhabitants in these areas and may be responsible for some cases of haemorrhagic fever, RVF is not the only cause of disease that is being observed in this outbreak. The Coordinating Group recognizes the need for comprehensive and well-designed studies and will request technical assistance and materials from international institutions. This will occur immediately.

Prompt investigation of active cases is required to determine the other causes of disease in this complex outbreak. Lack of the appropriate air transport needed to gain access to remote or flooded areas has been the single greatest impediment to the investigation. An appeal for helicopter transport is being made to other agencies.

Recommendations for the prevention of RVF, avoidance of insect bites and contact with sick livestock are still in effect. WHO recommends that travellers do not cancel their journeys to Kenya but they should be aware that Rift Valley fever is transmitted by mosquitoes. If they travel to areas near where outbreaks have been reported, they should take appropriate anti-insect measures. These include wearing long-sleeved shirts and long trousers and using mosquito repellant and bednets. Barrier nursing precautions are advised when caring for patients who are bleeding. More specific recommendations will be issued after the causes of other diseases involved in the epidemic are known.

 

16 January 1998

Rift Valley Fever in Kenya and Somalia

An outbreak similar to that reported in north-eastern Kenya has been reported in Somalia in the flooded area delimited by the towns of Belet Weyne and Johar on the Shabelle River. Four of 13 blood samples from suspected human cases have been positive for RVF.

The WHO team assembled in Kenya has established a small coordinating group for the Rift Valley Fever Task Force. It will comprise representatives from the Kenyan Government and from participating agencies and international organizations in Somalia and Kenya. This group will facilitate the rapid planning, coordination and implementation of surveillance and control activities. The surveillance system in both countries will be extended and strengthened in order to detect and confirm suspected cases. Standardized clinical case definitions and reporting methods will be used allowing for a better understanding of the epidemiology of the outbreak.

The WHO Collaborating Centre at the National Institute for Virology in Johannesburg has confirmed RVF virus infection in a second batch of 41 blood specimens. The virus was isolated in three specimens from human cases and six other specimens had IgM antibody indicating recent RVF virus infection. RVF virus was detected by PCR in one of seven blood specimens collected from goats.

Further details are given in the press release below.

Press Release WHO/9 - 16 January 1998

RIFT VALLEY FEVER OUTBREAK WIDESPREAD IN KENYA

The outbreak of Rift Valley fever, which had previously been reported in the North-eastern Province of Kenya, appears to be present in other parts of the country, according to WHO experts now in the country. Moreover, the outbreak is also equally serious in neighbouring Somalia.

Approximately 300 deaths from this outbreak have been reported to the Government in Nairobi. The World Health Organization (WHO) has received estimates of an approximately equal number of deaths due to the outbreak in Somalia.

The first reports came from the North-eastern Province in December 1997. In recent days, reports of humans and animals suffering from a disease with the symptoms of Rift Valley fever (RVF) have now been reported in Kenya's North-Eastern, Eastern, Rift Valley, Central and Coast provinces. These areas include some national parks and reported cases have also come from near Nairobi and Mombasa.

"At this point, we would not recommend that travellers cancel their journeys to Kenya but they should be aware that Rift Valley fever is transmitted by mosquitoes. If they travel to areas near where outbreaks have been reported, they should take proper anti-insect measures. These include wearing long-sleeved shirts and long trousers and using mosquito repellant and bednets," said Dr David Heymann, Director of WHO's Division of Emerging and other Communicable Diseases Surveillance and Control (EMC).

A second team of WHO experts arrived in Kenya on 15 January and, in collaboration with the Kenyan Ministry of Health, has elaborated a provisional plan to combat the outbreak. Elements of the plan include case-based, clinical surveillance in hospitals throughout Kenya to detect new cases and investigate the increased spread of the disease, and a systematic sampling and testing of specimens taken from humans and animals which have contracted the disease.

WHO is participating in a coordination group which has been established among the Kenyan ministries, international organizations and nongovernmental organizations involved in fighting the outbreak. Testing capacity for Rift Valley fever in humans at the WHO Collaborating Centre, the Kenya Medical Research Institute (KEMRI), has been established in collaboration with the WHO Collaborating Centre at the Centers for Disease Prevention and Control in Atlanta, USA.

For the moment, information on the outbreak from northeastern Kenya is still sparse and WHO and its partners will be working in coming weeks to increase surveillance of and testing for Rift Valley fever and other diseases potentially associated with this outbreak. Rift Valley fever may not be the sole cause of the outbreak, but recent evidence suggests that malaria and cholera are not playing as great a role as has been previously reported. Famine, on the other hand, has been a significant cause of death.

WHO will also be working with national and international partners to improve access to the northeast of Kenya, which has been largely cut off because of floods, and to develop a plan for control of the disease adapted to local conditions.

15 January 1998

Rift Valley fever in Kenya

Press Release WHO/7 - 15 January 1998

SECOND TEAM DEPARTS FOR KENYA TO INVESTIGATE AND CONTROL RIFT VALLEY FEVER OUTBREAK

The World Health Organization (WHO) has sent a second team to Kenya to work with the national authorities and international agencies, such as the Food and Agriculture Organization, the International Federation of Red Cross and Red Crescent Societies, the International Livestock Research Institute (ILRI), Médecins Sans Frontières and Epicentre (Paris), to further investigate the outbreak of Rift Valley fever (RVF) in north-eastern Kenya and develop control measures.

WHO has had a team working in Kenya since the outbreak was first announced. The second team arrived in Nairobi on Thursday, 15 January. This team, which consists of public health specialists in Rift Valley fever, will coordinate activities in Kenya in the health field, further assess the extent of the outbreak, strengthen control measures among humans and animals, and explore the feasibility of immunizing livestock to prevent further spread.

Specimens have been obtained from sick humans and animals at two different times by local WHO teams and these have been tested at the WHO Collaborating Centres at the National Institute of Virology, Johannesburg, South Africa, and the Centers for Disease Control and Prevention, Atlanta, USA. The human tests indicate that at least 13 of the first 36 people examined were infected with the RVF virus and study of animal specimens has confirmed that animals are likewise infected.

Access to the outbreak area has been difficult due to the current floods and the initial WHO investigation was unable to completely clarify the extent to which other causes have contributed to the high mortality among both humans and animals. Estimates of human fatalities due to the current outbreak currently range as high as 450 and it is suspected that other diseases such as malaria, and possibly cholera, are also contributing to the high number of deaths.

 

14 January 1998

Rift Valley fever in Kenya

Investigation of the specimens with ELISA test at the WHO Collaborating Centre at Centers for Disease Control and Prevention, in Atlanta detected IgM antibody which indicates recent RVF infection in 13 of 36 cases. In addition to the 3 RVF virus isolates reported in the first week of January by the WHO Collaborating Centre at the National Institute of Virology, Johannesburg the virus has been isolated from another case tested in the first batch of 36 specimens and in 3 cases tested in a second batch which was received on 9 January. These results all concerned human cases affected by the outbreak which may have killed over 300 people and many animals in the Garissa District, North-Eastern Province, Kenya since early December. Laboratory investigations of specimens from animals are in progress in South Africa.

Access to the outbreak area has been difficult and the initial WHO investigation was unable to completely clarify the extent to which other causes have contributed to the high mortality among both humans and animals. WHO is sending a follow-on team to work with the national authorities and international agencies, such as the Food and Agriculture Organization, the International Federation of Red Cross and Red Crescent Societies, Médecins Sans Frontières, and Epicentre (Paris) to further investigate the outbreak and develop control measures. The main objectives are to coordinate activities, assess the extent of the outbreak and strengthen control measures among humans and animals and explore the feasibility of immunization of livestock.

 

6 January 1998

Rift Valley fever, in Kenya

Rift Valley fever has been confirmed in an outbreak which affected humans and domestic animals (goat, sheep, cattle and camels) in Garissa District, a remote area of north-eastern Kenya. The outbreak area is difficult to access and the full extent of the outbreak is not yet known but reports indicate that up to 300 people may have died from the disease.

The first evidence that Rift Valley fever was responsible for the outbreak was obtained on 31 December in the WHO Collaborating Centre at the National Institute for Virology, Johannesburg, South Africa. In testing the first sera available from the outbreak (from 36 human cases and one calf), four sera were PCR-positive and RVF was subsequently confirmed when the virus was isolated from three of them. Antibody to RVF virus was detected in 17 sera by either indirect immunofluorescence or IgG or IgM ELISA tests. Eight of 12 sera which could be retested had haemagglutination inhibition antibody to RVF.

Because the population affected is undernourished and subject to various diseases, particularly those associated with a lack of clean drinking water and of health services, other severe diseases that normally occur in the area, such as shigellosis and malaria, may partially explain the large number of deaths in the region.

Additional epidemiological studies using a uniform case definition are needed to better understand the scope and nature of the epidemic as well as the support and control measures required. Laboratory investigations, including on samples taken from animals, are continuing at NIV and another WHO Collaborating Centre, the Centers for Disease Control and Prevention (CDC) in Atlanta, USA.

Rift Valley fever virus is a member of the family Bunyaviridae and is in the Phlebovirus genus. The virus was first isolated in 1931 during a disease outbreak in livestock on a farm located in the Rift Valley of Kenya. The virus is endemic to Africa, south of the Sahara desert, but infections have periodically extended into Egypt. During epizootics (epidemics in animals), the virus causes spontaneous abortion in ewes and cows and deaths in lambs and calves. In humans, the virus produces a usually non-fatal dengue-like illness. Less frequently, infection results in retinitis, encephalitis and haemorrhagic disease, the latter condition being consistent with the present outbreak. Rift Valley fever virus is transmitted by mosquitoes and many different species can serve as vectors. Humans can also be infected by contact with blood or body fluids from infected animals which may occur during slaughtering of the animals or handling of aborted foetuses. The risk of human-to-human infection through direct contact appears to be very low.

WHO does not recommend any restrictions on travel to Kenya as the area affected is remote and far from the tourist centres of Nairobi, Mombassa and the game parks.

 

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