Identification of potential vectors of and detection of antibodies against Rift Valley fever virus in livestock during interepizootic periods

Melinda K. Rostal Department of Veterinary Biomedical Sciences, College of Veterinary Medicine, and the School of Public Health, University of Minnesota, Saint Paul, MN 55108.

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Alina L. Evans Department of Veterinary Biomedical Sciences, College of Veterinary Medicine, and the School of Public Health, University of Minnesota, Saint Paul, MN 55108.

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Rosemary Sang Kenya Medical Research Institute, Nairobi, Kenya.

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Solomon Gikundi International Emerging Infections Program, Centers for Disease Control and Prevention—Kenya, Unit 64112, APO, AE 09831, Nairobi, Kenya.

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Lilian Wakhule International Emerging Infections Program, Centers for Disease Control and Prevention—Kenya, Unit 64112, APO, AE 09831, Nairobi, Kenya.

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Peninah Munyua International Emerging Infections Program, Centers for Disease Control and Prevention—Kenya, Unit 64112, APO, AE 09831, Nairobi, Kenya; and Directorate of Veterinary Services, Central Veterinary Laboratories, Kabete, Nairobi, Kenya.

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Joseph Macharia Directorate of Veterinary Services, Central Veterinary Laboratories, Kabete, Nairobi, Kenya.

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Daniel R. Feikin International Emerging Infections Program, Centers for Disease Control and Prevention—Kenya, Unit 64112, APO, AE 09831, Nairobi, Kenya.

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Robert F. Breiman International Emerging Infections Program, Centers for Disease Control and Prevention—Kenya, Unit 64112, APO, AE 09831, Nairobi, Kenya.

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M. Kariuki Njenga Department of Veterinary Biomedical Sciences, College of Veterinary Medicine, University of Minnesota, Saint Paul, MN 55108; and International Emerging Infections Program, Centers for Disease Control and Prevention—Kenya, Unit 64112, APO, AE 09831, Nairobi, Kenya.

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DOI:
https://doi.org/10.2460/ajvr.71.5.522
Volume/Issue:
Volume 71: Issue 5
Online Publication Date:
01 May 2010
Restricted access
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Abstract

Objective—To evaluate the prevalence of Rift Valley fever virus (RVFV) antibodies in livestock and presence of competent mosquito vectors of RVFV during an interepizootic period (IEP) in Kenya.

Animals—208 sheep and 84 goats ranging in age from 4 months to 15 years, from 2 breeding herds.

Procedures—Blood specimens were collected from the sheep and goats during the 1999–2006 IEP in Rift Valley Province, and serum was harvested. Serum specimens were tested for IgG and IgM antibodies against RVFV by use of an ELISA. In addition, 7,134 mosquitoes were trapped in Naivasha, Nairobi, and Northeastern Province, and speciation was performed.

Results—No animals were seropositive for IgM against RVFV. Of the animals born after the 1997–1998 epizootic, 18% (34/188) of sheep were seropositive for IgG against RVFV, compared with 3% (2/75) of goats. Seventy percent (8,144/11,678) of the mosquitoes collected were of the Culex subgenera; 18% (2,102/11,678) were Aedes spp.

Conclusions and Clinical Relevance—Detection of IgG in the sera of sheep and goats born after the 1997–1998 epizootic and before the 2006 epizootic indicated that virus activity existed during the IEP. Detection of Aedes mosquitoes, which are competent vectors of RVFV, suggested that a cryptic vector-to-vertebrate cycle may exist during IEPs.

Abstract

Objective—To evaluate the prevalence of Rift Valley fever virus (RVFV) antibodies in livestock and presence of competent mosquito vectors of RVFV during an interepizootic period (IEP) in Kenya.

Animals—208 sheep and 84 goats ranging in age from 4 months to 15 years, from 2 breeding herds.

Procedures—Blood specimens were collected from the sheep and goats during the 1999–2006 IEP in Rift Valley Province, and serum was harvested. Serum specimens were tested for IgG and IgM antibodies against RVFV by use of an ELISA. In addition, 7,134 mosquitoes were trapped in Naivasha, Nairobi, and Northeastern Province, and speciation was performed.

Results—No animals were seropositive for IgM against RVFV. Of the animals born after the 1997–1998 epizootic, 18% (34/188) of sheep were seropositive for IgG against RVFV, compared with 3% (2/75) of goats. Seventy percent (8,144/11,678) of the mosquitoes collected were of the Culex subgenera; 18% (2,102/11,678) were Aedes spp.

Conclusions and Clinical Relevance—Detection of IgG in the sera of sheep and goats born after the 1997–1998 epizootic and before the 2006 epizootic indicated that virus activity existed during the IEP. Detection of Aedes mosquitoes, which are competent vectors of RVFV, suggested that a cryptic vector-to-vertebrate cycle may exist during IEPs.

Contributor Notes

The authors thank Drs. Kathryn Diehl, Marguerite Pappaioanou, and Jeff Bender for technical assistance.

Supported by the CDC, the Morris Animal Foundation, the University of Minnesota Judd Fellowship, the University of Minnesota Dr. J Arthur Meyers Endowment for International Experience in Public Health, and the University of Minnesota College of Veterinary Medicine Travel Grant and Summer Scholars program.

Address correspondence to Dr. Njenga (Knjenga@ke.cdc.gov).
Cover American Journal of Veterinary Research
American Journal of Veterinary Research
Publication Date:
01 May 2010
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