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Detection by Two Enzyme-Linked Immunosorbent Assays of Antibodies to Ehrlichia ruminantium in Field Sera Collected from Sheep and Cattle in Ghana

Lesley Bell-Sakyi,^1,2* Enoch B. M. Koney,¹ Otilia Dogbey,¹ Keith J. Sumption,^2, Alan R. Walker,² Alasdair Bath,^2, and Frans Jongejan³

Veterinary Services Department, Ministry of Food and Agriculture, Accra, Ghana,¹ Centre for Tropical Veterinary Medicine, University of Edinburgh, Easter Bush, Roslin, Midlothian EH25 9RG, United Kingdom,² Division of Parasitology and Tropical Veterinary Medicine, Faculty of Veterinary Medicine, Utrecht University, 3508TD Utrecht, The Netherlands, and Department of Veterinary Tropical Diseases, Faculty of Veterinary Science, University of Pretoria, Onderstepoort 0110, South Africa³

Received 4 March 2003/ Returned for modification 1 May 2003/ Accepted 27 June 2003

Two serological tests for detection of antibodies to Ehrlichia (previously Cowdria) ruminantium, the causative agent of heartwater, were compared by using field sera collected from sheep and cattle as part of serosurveys in Ghana. Sera selected as either negative or positive by a new polyclonal competitive enzyme-linked immunosorbent assay (PC-ELISA) were tested by the indirect MAP1-B ELISA. Cutoff values of 14 percent positivity (14 PP) for both ruminant species were obtained for the MAP1-B ELISA by using preseroconversion Ghanaian sera and were compared with previously recommended cutoff values of 29 PP for sheep and 38 PP for cattle. With the 14-PP cutoff, of 151 sheep sera which tested negative by PC-ELISA, 89% were also negative by MAP1-B ELISA, while of 419 sheep sera positive by PC-ELISA, 98% were also positive by MAP1-B ELISA. Of 261 bovine sera negative by PC-ELISA, 82% were also negative by MAP1-B ELISA. Of 511 bovine sera positive by PC-ELISA, only 47% were positive by MAP1-B ELISA; these included 168 sera collected from cattle following first seroconversion as detected by both tests, with 125 of these sera positive by PC-ELISA but only 59 and 5 positive by MAP1-B ELISA with the 14- and 38-PP cutoff levels, respectively. These results indicate that both assays are highly sensitive and specific for detection of E. ruminantium exposure in sheep but that the MAP1-B ELISA lacks sensitivity for postseroconversion bovine sera in comparison to the PC-ELISA. Both tests confirm E. ruminantium seroprevalence of at least 70% in Ghanaian sheep; levels of exposure among Amblyomma variegatum-infested Ghanaian cattle are likely to be higher than the seroprevalence value of 66% obtained with the PC-ELISA.

Present address: Food and Agriculture Organization of the United Nations, Via delle Terme di Caracalla, 00100 Rome, Italy.

Present address: 26 Merchiston Park, Edinburgh, United Kingdom.

This article has been cited by other articles:

• Faburay, B., Munstermann, S., Geysen, D., Bell-Sakyi, L., Ceesay, A., Bodaan, C., Jongejan, F. (2005). Point Seroprevalence Survey of Ehrlichia ruminantium Infection in Small Ruminants in The Gambia. CVI 12: 508-512 [Abstract] [Full Text]