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Rift Valley fever in the Sudan
TRANSXTIONSOF THE ROYALSOCIETY OF TROPICAI.MEDICINE AND HYGIENE(1990)
Rift Valley fever in the Sudan Veterinay Research Laboratory, P.O. F. G. Davies Kabete, Kenya
Clinical Rift Valley fever (RVF) was first identified in domestic r uminants in epizootic form in the Sudan in 1973 (EISA et al., 1977). The epizootic was remarkable for the high mortality encountered in the local breeds, with 90% deaths in lambs, 70% in older sheep, 50% in goats and 20% in calves. Such severe diseaseis seen in RVF epixootics in East and South Africa only in the highly susceptible imported breeds. The indigenous sheep, goats and cattle throughout most of the Ethiopian faunal region are relatively insusceptible to RVF (DAVIES, 1975; FAGBAMI et al., 1975). In Kenya most indigenous zebu type cattle and the local hair sheepbreeds-showonly a short period of nvrexia and viraemia after RVF infection. * -The epizootic occurred in the Upper and Blue Nile Provinces, south of Khartoum, close to the extensive irrigation schemes of the Gezira. Disease was first seen in the low lying swampy areasclose to the Nile and its tributaries. The origin of the virus in this 1973 epixootic was not established. RVF may be endemic in the region, although the investigators considered that it had been introduced (EISA et al., 1977). The existence of foci endemic for RVF in the Sudan was suggestedby the finding of RVF antibody in 4 human sera from Kordofan Province, south of the Nubian mountains (31”7’E; 10’8’N) and west of the White Nile (31”E; lO”25’N) (FINDLAY et al., 1936). A biotype peculiar to- the Sudan is the tuich (ANDREWS. 1948). seasonallv flooded erasslands in
the catchment &ea of the White Rile and its tributaries, which form a large part of the south-east of the country. These grasslandsare flooded annually for a period of 6-12 weeks, after which they are extensively grazed by cattle of the Dinka tribe. Studies in Kenya (DAVIES, 1975; LINTHICUM et al., 1985) have shown that flooding of grasslands may be
important in the generation of epixootics of RVF. One of -the commonest floodwater breeding species of Aedes was canable of transmittine RVF virus transovarially (LI~THICUM et al., 1981;1).
141
84, 141
About 2400 cattle sera were collected in 1979-1981 from the t&h region near Wau (7”42’N; 28”E), Gogrial (8”2l’N; 28”5’E), and Aweil (8”45’N, 27”15’E). The sera were inactivated at 56°C for 30 min and were examined for neutralizing antibody to the Kabete strain of RVF virus. Sera were diluted from 1:40 to 1:160 and were tested in duplicate against 50-75 tissue culture 50% infective doses (TCIDS~) of virus. The assaywas performed in Vero cells. Sera neutralizing 80% or more of the challenge virus at 1:40 or higher dilutions were considered positive; 14% of the 2400 examined were positive and nearly all had titres of 1:160 or greater. This percentage of positive sera suggests that the cattle may have been exposed to a low level of virus-vector activity each year, such as occurs in RVF enxootic areas elsewhere in Africa (unpublished observations). Alternatively they may have been involved in the regional epizootics which occurred in 1977-1979. This survey has shown that the cattle in the toich have experienced some contact with RVF virus. The possibility exists that epizootics may occur and involve the many homeless people at present in this region. Further RVF enzootic areasmay exist in the Sudan in the higher rainfall grasslands with gallery and depression forests in Equatoria Province and in the riverine marshlands in Upper and Blue Nile Provinces. References Andrews, G. (1948). In: Agriculture in the Sudan, Tothill, J. D. (editor). Oxford: Oxford University Press. Davies, F. G. (1975). Observations on the epidemiology of Rift Valley fever in Kenya. Journal of Hygiene, 75, 219-230. Eisa, M., Obeid, H. M. A. & El Sawi, A. S. A. (1977). Rift Valley fever in the Sudan. Bulletin of Animal Health and Production in Africa,
25, 343-347.
Fagbami, A. H., Tomori, O., Fabiyi, A. & Isoun, T. T. (1975). Experimental Rift Valley fever in West African dwarf sheep. Research in Veterinay Science, 18,334-335. Findlay, G. J., Stefanopoulo, G. M. & Mac&Bum, F. (1936). Presenced, anticorps contre la fihre de la Valke du Rift dartsle sangdes Africains. Bulletin de la So&d de Pathologic Ewotique, 29, 986996.
Lintbicum, K. J., Davies, F. G.? Kairo, A. & Bailey, C. L. (1985). Rift Valley fever vrrus (family Bunyaviridae, genus Phkbmim). Isolations from Diptera collected during an interepizootic period. Journal of Hygiene, 95, 197-209.
Received 17 August 1989; accepted fm publication 4 September 1989
Rift Valley fever in the Sudan Veterinay Research Laboratory, P.O. F. G. Davies Kabete, Kenya
Clinical Rift Valley fever (RVF) was first identified in domestic r uminants in epizootic form in the Sudan in 1973 (EISA et al., 1977). The epizootic was remarkable for the high mortality encountered in the local breeds, with 90% deaths in lambs, 70% in older sheep, 50% in goats and 20% in calves. Such severe diseaseis seen in RVF epixootics in East and South Africa only in the highly susceptible imported breeds. The indigenous sheep, goats and cattle throughout most of the Ethiopian faunal region are relatively insusceptible to RVF (DAVIES, 1975; FAGBAMI et al., 1975). In Kenya most indigenous zebu type cattle and the local hair sheepbreeds-showonly a short period of nvrexia and viraemia after RVF infection. * -The epizootic occurred in the Upper and Blue Nile Provinces, south of Khartoum, close to the extensive irrigation schemes of the Gezira. Disease was first seen in the low lying swampy areasclose to the Nile and its tributaries. The origin of the virus in this 1973 epixootic was not established. RVF may be endemic in the region, although the investigators considered that it had been introduced (EISA et al., 1977). The existence of foci endemic for RVF in the Sudan was suggestedby the finding of RVF antibody in 4 human sera from Kordofan Province, south of the Nubian mountains (31”7’E; 10’8’N) and west of the White Nile (31”E; lO”25’N) (FINDLAY et al., 1936). A biotype peculiar to- the Sudan is the tuich (ANDREWS. 1948). seasonallv flooded erasslands in
the catchment &ea of the White Rile and its tributaries, which form a large part of the south-east of the country. These grasslandsare flooded annually for a period of 6-12 weeks, after which they are extensively grazed by cattle of the Dinka tribe. Studies in Kenya (DAVIES, 1975; LINTHICUM et al., 1985) have shown that flooding of grasslands may be
important in the generation of epixootics of RVF. One of -the commonest floodwater breeding species of Aedes was canable of transmittine RVF virus transovarially (LI~THICUM et al., 1981;1).
141
84, 141
About 2400 cattle sera were collected in 1979-1981 from the t&h region near Wau (7”42’N; 28”E), Gogrial (8”2l’N; 28”5’E), and Aweil (8”45’N, 27”15’E). The sera were inactivated at 56°C for 30 min and were examined for neutralizing antibody to the Kabete strain of RVF virus. Sera were diluted from 1:40 to 1:160 and were tested in duplicate against 50-75 tissue culture 50% infective doses (TCIDS~) of virus. The assaywas performed in Vero cells. Sera neutralizing 80% or more of the challenge virus at 1:40 or higher dilutions were considered positive; 14% of the 2400 examined were positive and nearly all had titres of 1:160 or greater. This percentage of positive sera suggests that the cattle may have been exposed to a low level of virus-vector activity each year, such as occurs in RVF enxootic areas elsewhere in Africa (unpublished observations). Alternatively they may have been involved in the regional epizootics which occurred in 1977-1979. This survey has shown that the cattle in the toich have experienced some contact with RVF virus. The possibility exists that epizootics may occur and involve the many homeless people at present in this region. Further RVF enzootic areasmay exist in the Sudan in the higher rainfall grasslands with gallery and depression forests in Equatoria Province and in the riverine marshlands in Upper and Blue Nile Provinces. References Andrews, G. (1948). In: Agriculture in the Sudan, Tothill, J. D. (editor). Oxford: Oxford University Press. Davies, F. G. (1975). Observations on the epidemiology of Rift Valley fever in Kenya. Journal of Hygiene, 75, 219-230. Eisa, M., Obeid, H. M. A. & El Sawi, A. S. A. (1977). Rift Valley fever in the Sudan. Bulletin of Animal Health and Production in Africa,
25, 343-347.
Fagbami, A. H., Tomori, O., Fabiyi, A. & Isoun, T. T. (1975). Experimental Rift Valley fever in West African dwarf sheep. Research in Veterinay Science, 18,334-335. Findlay, G. J., Stefanopoulo, G. M. & Mac&Bum, F. (1936). Presenced, anticorps contre la fihre de la Valke du Rift dartsle sangdes Africains. Bulletin de la So&d de Pathologic Ewotique, 29, 986996.
Lintbicum, K. J., Davies, F. G.? Kairo, A. & Bailey, C. L. (1985). Rift Valley fever vrrus (family Bunyaviridae, genus Phkbmim). Isolations from Diptera collected during an interepizootic period. Journal of Hygiene, 95, 197-209.
Received 17 August 1989; accepted fm publication 4 September 1989