"Having just returned from Kenya and Ethiopia, I am now in a position to provide some information. I am grateful to the Kenyan Veterinary and Medical Services, the Tanzanian Department of Livestock Development, the Ethiopian Veterinary Team, members of the WHO team in Kenya and many individuals who have provided the information on which the analysis is based.
This brief summary deals primarily with the livestock disease situation; reports from WHO will provide the human disease dimension. In addition to attempting to describe the existing situation. I have added some indication of the possible developments in the near future.
THE SITUATION IN KENYA AND SOMALIA Rift Valley Fever Historically, within the Horn of Africa, RVF epidemics have occurred in Rift Valley and Central Provinces of Kenya at prolonged intervals over 70 years or more. Northern Tanzania forms part of this disease zone but RVF occurrence in north-eastern Kenya has been a rare event in the past. The climatic factors favouring its emergence from the area in which the infection persists have been well studied and it is known that epidemics follow heavy and prolonged, often unseasonal, rainfall. Examination of remote sensing data at FAO for the past five months indicates that such conditions had prevailed in Kenya at the end of 1997. In appreciation of the risk the Kenya Veterinary Service (KVS) warned farmers of the risk and advised vaccination of high potential livestock. Livestock vaccinated in December appear to have been protected. The remote sensing data also indicate that suitable conditions for the explosive multiplication of mosquito vectors existed and persist over extensive areas of Kenya, southern Somalia, south-eastern and southern Ethiopia, eastern Uganda, southern Sudan and northern Tanzania. Reports and investigations by the KVS, backed up by laboratory confirmation, are consistent with the understanding that RVF has been occurring in December 1997 and January 1998, primarily in sheep, cattle and camels, in Central and Rift Valley Provinces and the west of Eastern Province of Kenya. The disease pattern here has been typical with fever, abortion (the predominant feature), early neonatal death, jaundice and death predominantly in young animals, and a fall in milk yield in dairy cattle. Humans have generally suffered an influenza-like disease with few complications.
From mid-December 1997, a fatal haemorrhagic fever of humans has been affecting people in Wajir, Garissa and Tana River Districts of North-eastern and Eastern Provinces of Kenya and in southern Somalia. Rift Valley fever (RVF) virus has been identified as a causal agent in this epidemic. RVF-associated human haemorrhagic disease has also been confirmed west of Magadi in Rift Valley Province of Kenya. Reports of similar human disease in the north of Somalia (Erigavo, Bosaso, Hargeisa) have not been confirmed; investigations are in progress.
At the same time the presence of RVF associated with livestock disease has been confirmed in north-eastern Kenya and southern Somalia. The abortions reported in camels and goats are consistent with the diagnosis of RVF, as could also be some reports of disease and mortality, some associated with blood stained discharges. Abortions of livestock have also been reported from southern Kenya associated temporally with confirmed RVF in humans. However, other reports of high morbidity and mortality in camels, small ruminants and cattle (the last in a limited area of Lower and Middle Juba Regions of Somalia), and the few descriptions of clinical signs, are not consistent with RVF. I am not aware of any reports of unusual livestock morbidity in the northern part of Somalia.
Other Livestock Diseases The conditions prevailing in the affected area favour the generation of large populations of mosquitoes, midges and biting flies and, therefore, an increase in incidence of many of the diseases they transmit was to be expected. Not surprisingly disease with signs typical of bluetongue is reported to be affecting improved breeds of sheep (wool sheep, Dorpers and their crosses) in Kenya away from the northeast and in northern Tanzania. As expected indigenous sheep and goats do not feature in reports.
Initial suspicions of anthrax have not been borne out by subsequent investigations, albeit limited. However, the disease could still be a component of the animal mortality reported and merits consideration, especially later as the land dries out.
Investigations in NE Kenya and Somalia have been severely hampered by flooding but investigations are proceeding. The aetiology of the livestock diseases is not fully established. The understanding presented here will certainly be amended as more information becomes available. The peak of the RVF epidemic may now have passed in Kenya and Somalia.
Superimposed on the effects of RVF, other aetiological components which are likely to be contributing are, by species and disease:
Small Ruminants
resulting from environmental factors: heavy mortality of small ruminants was associated with the flooding, peaking in NE Kenya in December. "Foot rot" appears to be widespread as a consequence of long immersion of the feet in water and mud; loss of the hooves is reported and ventral dermatitis. Secondary bacterial infection and pain preventing movement to find food probably resulted in high mortality. It is to be expected that the stress of heavy rainfall following drought conditions and combined with malnutrition predisposed them to disease conditions such as pneumonic pasteurellosis.
Contagious caprine pleuropneumonia (CCPP) was confirmed by the KVS to have been the cause of respiratory disease and mortality in goats near to Garissa in early January. It is endemic to the pastoral communities of northern Kenya, southern Ethiopia and southern Somalia and is suspected to be causing significant mortality.
Peste des petits ruminants (PPR) is considered by the Ethiopian Veterinary Team to be endemic in south-west Ethiopia and was confirmed to be present in 1997 in the Somali and Oromiya Regional States of Ethiopia. During 1997, clinical reports from field operatives in central and southern Somalia described a disease syndrome highly suggestive of PPR. Although clinical PPR has never been identified in Kenya, the Kenya Agricultural Research Institute detected antibodies to PPR in sera collected from 1981 to 1985 in the border areas of western and northern Kenya. Consequently, the risk of PPR introduction and/or spread must be considered to be high.
Helminthosis, primarily the stomach worm causing haemonchosis, develops rapidly in suitable conditions of soil moisture and high ambient temperature. Severely anaemic sheep with bottle jaw were indeed found to have heavy burdens of Haemonchus in Kenya. An increase in incidence with high mortality could be expected to occur as pastures dry out.
Cattle
Cattle have not featured highly in disease reports from the affected areas except for some reports of unusual mortality from Middle and Lower Juba Regions of Somalia in January. A clear clinical case description is lacking. In 1996 the KVS reported the presence of rinderpest in the Mandera district of North-east Province and since then the disease has been under surveillance and intensive control activities. There was an unconfirmed report of a clinical syndrome suggestive of rinderpest in Gedo Region of Somalia in March/April 1997. It is important that veterinary services, including those of NGOs, be alerted to the significance of occurrence of a clinical syndrome which could be suggestive of rinderpest. Any suspicious signs must be reported to the official veterinary service in order that prompt action can be taken.
Foot-and-mouth disease (FMD) was present in the Somali Regional State of Ethiopia, near the border with Kenya, in mid 1997. Clearly, there exists a risk of dissemination of this infection.
Camels
Many reports of high mortality in camels have been received from throughout the affected area. The abortion storms described are consistent with RVF being a cause as is some mortality in young animals. Other descriptions of morbidity and mortality are highly suggestive of camel pox (or the rarer parapox) - swelling of the labia and head, lesions on the inside (overlain by a diphtheritic membrane) and outside of the labia, blockage of the nares. A "camel respiratory disease syndrome" is a relatively new disease which spread in epidemic form in recent years from Sudan through Eritrea, Ethiopia and Djibouti into Somalia and NE Kenya. Its cause is unknown. One group of researchers has suggested that PPR virus might be involved whilst others favour an aetiology involving mycoplasma and/or pasteurellosis because of suggestive pathology and response to antibiotic therapy. After the initial epidemic abated, a resurgence of this disease is known to have been occurring in the Afar and Somali Regional States of Ethiopia in 1997 and it was also present in Somalia. It is possible that this disease could be contributing to the morbidity; mortality can be high.
Wildlife The disease which killed some 200 Gerenuk in northern Kenya in December 1997 to January 1998 was characterised by oral hyperaemia and coronitis raising suspicions that BT or EHD could be responsible. Examinations are still pending but no further wildlife mortalities have been reported even in game in close contact with livestock.
Other Considerations/Risks:
With high populations of biting flies and midges, it is likely that lumpy skin disease and ephemeral fever will become prevalent in the near future.
Tick burdens are likely to increase considerably as the land dries, causing an increase in direct damage (-tick worry- including foot abscessation ). Nairobi sheep disease epidemics could be experienced, causing abortion storms and mortality in indigenous sheep and goats, resembling RVF. East Coast fever could extend well outside its normal range.
Contagious bovine pleuropneumonia (CBPP) is endemic in the area and mixing of cattle herds with crowding provides ideal conditions for transmission.
Several different leptospiral serovars (L. grippotyphosa and L. icterohaemorrhagiae, for example) cause disease in a broad range of livestock species, primarily in humid conditions. This is usually marked by fever, abortion in pregnant females, haemoglobinuria, jaundice with moderate to high mortality, closing resembling RVF. Leptospirosis needs to be considered in differential diagnosis.
Tse-tse fly transmitted trypanosomosis of cattle is normally present in southern Somalia and neighbouring Kenya; it is thought to have been increasing in incidence in NE Kenya before the recent events. Favourable conditions for tse-tse fly multiplication could be provided as the land dries out and infection rates could increase. An increase in incidence could also occur from mechanical transmission by biting flies which are prevalent. Surra (Trypanosoma evansi infection) is prevalent in camel populations in the region in normal times and an increase in incidence would be expected to follow the increase in the numbers of biting flies favoured by high soil moisture.
TANZANIA
On 5/1/98 a team from the Veterinary Investigation Centre, Arusha, visited a ranch in western Kilimanjaro Region of northern Tanzania to investigate reported mortality, from December 1997, in cattle and Black-headed Persian sheep. In the sheep particularly, their findings were strongly indicative of an outbreak of BT. Samples have been taken and confirmation is awaited.
ETHIOPIA
Investigations by the Ethiopian veterinary services in South Omo district of south-west Ethiopia from 11 to 17 Jan concluded that there was no unusual morbidity of livestock or people although there has been extensive flooding and conditions for vector multiplication are ideal.
The Ethiopian veterinary services are actively investigating the possibility that the same disease epidemic conditions as were experienced in Kenya and Somalia could have extended to include the south-eastern part of Ethiopia. Reports of human illness are also being followed up by the medical services. --Peter Roeder, FAO EMPRES, <Peter.Roeder@fao.org> on ProMED-mail <promed@usa.healthnet.org>.