Isolation of a new flavivirus related to cell fusing agent virus (CFAV) from field-collected flood-water Aedes mosquitoes sampled from a dambo in central Kenya.

Cell fusing agent virus (CFAV) is an RNA insect virus that was isolated from a line of Aedes aegypti mosquito cells and has been assigned to the family Flaviviridae, genus Flavivirus. We report here the first isolation of a CFA-like virus from field-collected mosquitoes. Mosquito larvae and pupae were sampled from flooded dambos in Central Province, Kenya during the short rain season of 1999. Specimens were reared to adults, identified and pooled by species and were tested for the presence of virus. Two virus isolates were obtained from two pools of Aedes macintoshi mosquitoes. The virus isolates replicated only in invertebrate cells in culture and not in vertebrate cells or in mice. The virus isolates did not antigenically cross-react with known arboviruses but were identified to family by reverse-transcriptase polymerase chain reaction (RT-PCR) performed using primers specific to alphaviruses, bunyaviruses and flaviviruses; only the flavivirus-specific primers produced a DNA fragment of the expected size. Nucleic acid sequencing of this fragment showed the two isolates to be nearly identical. Comparison of sequences to the GenBank database using BLAST identified the virus as most closely related to CFAV. Results from cross-neutralization tests suggested that, although the BLAST search indicated homology to CFAV, the virus isolated represented a new insect flavivirus. Detailed characterization of this new virus, described in Crabtree et al. [7], further supports this finding. We propose this new flavivirus be designated Kamiti River virus (KRV). This is the first isolation of a CFA-like virus from field-collected mosquitoes and indicates the presence of this group of viruses in nature.

Viral haemorrhagic fever surveillance in Kenya, 1980-1981.

Following two cases of Marburg virus disease in Kenya in 1980, viral haemorrhagic fever surveillance was undertaken in western Kenya. Over a 21-month period investigations, including virus isolation attempts, patient and contact serology, visits to areas where suspected cases occurred, interviewing family members and neighbours of suspected cases and following up any additional illnesses in these areas, were carried out. During the study two cases were found that were likely to have been Ebola haemorrhagic fever based on rising antibody titres or positive serology in contacts. Diagnoses of hepatitis A, hepatitis B, malaria, bacterial septicaemia or other causes were arrived at in 24 cases. No diagnosis could be made in 26 instances. 741 human sera were tested for antibodies against Marburg, Ebola, Congo haemorrhagic fever, Rift Valley fever or Lassa fever viruses by indirect fluorescence. Eight sera were positive for Ebola virus antibodies, all of which were from suspected cases or contacts of suspected cases. Two sera were antibody positive to Congo virus and one had antibodies against Rift Valley fever virus. No Marburg or Lassa virus antibodies were detected.

Antibodies against haemorrhagic fever viruses in Kenya populations.

Human sera from Lodwar (77 sera), Nzoia (841 sera), Masinga (251 sera), Laisamis (174 sera) and the Malindi/Kilifi area (556 sera) in Kenya were tested by indirect immunofluorescence for antibodies against Marburg, Ebola (Zaire and Sudan strains), Congo haemorrhagic fever, Rift Valley fever and Lassa viruses. Antibodies against Ebola virus, particularly the Zaire strain, were detected in all regions and were, over-all, more abundant than antibodies against the other antigens. Ebola and Marburg antibody prevalence rates were highest in the samples from Lodwar and Laisamis, both semi-desert areas. Antibodies against Rift Valley fever virus were also highest in the Lodwar sample followed by Malindi/Kilifi and Laisamis. Congo haemorrhagic fever virus antibodies were rare and no antibodies against Lassa virus were detected in the 1899 sera tested.

Marburg, Ebola and Rift Valley Fever virus antibodies in East African primates.

Sera from 464 primates held at four institutes in Kenya were tested by indirect immunofluorescence for the presence of antibodies against Marburg, Ebola, Congo haemorrhagic fever, Rift Valley fever and Lassa viruses. Four of 136 vervet monkeys were positive for Marburg virus antibodies and three of 184 baboons had antibodies against Ebola virus. One baboon was positive for Marburg virus antibodies. Two vervet monkeys, three baboons and one grivet monkey (of 56 tested) had antibodies against Rift Valley fever virus. No Congo or Lassa virus antibodies were detected. A sample of 88 sera of more arboreal primates (Sykes, blue and colobus monkeys) were negative against all five antigens, as were sera from 58 staff members of the institutes who worked with or near the animals.

Recovery of o'nyong-nyong virus from Anopheles funestus in Western Kenya.

O'nyong-nyong (ONN) virus first appeared nearly 20 years ago and was responsible for one of the largest arbovirus outbreaks ever documented. Since the original outbreak ended, ONN activity, as determined serologically, gradually declined on the Kano Plain in western Kenya. In June, 1978, a virus similar or identical to ONN was isolated from a pool of Anopheles funestus Giles captured at Ahero on the Kano Plain. The possible implications of this isolation are discussed.