MERS Coronavirus Neutralizing Antibodies in Camels, Eastern Africa, 1983–1997

Abstract

To analyze the distribution of Middle East respiratory syndrome coronavirus (MERS-CoV)-seropositive dromedary camels in eastern Africa, we tested 189 archived serum samples accumulated during the past 30 years.We identified MERS-CoV neutralizing antibodies in 81.0% of samples from the main camel-exporting countries, Sudan and Somalia, suggesting long-term virus circulation in these animals.S ince 2012, a newly emerged human pathogenic coro- navirus (CoV) has caused an ongoing epidemic on the Arabian Peninsula.The designated Middle East respiratory syndrome (MERS)-CoV belongs to the Betacoronavirus genus lineage C and causes severe respiratory disease in humans (1).As of July 2, 2014, MERS-CoV has caused ≈842 human infections, including 322 deaths (2).Dromedary camels are a putative source for MERS-CoV infection in humans.Dromedaries from countries in Africa (Egypt, Tunisia, Nigeria, Sudan, Ethiopia, and Kenya) and Arabia (United Arab Emirates, Saudi Arabia, Oman, Qatar, and Jordan) have shown high rates of MERS-CoV seropositivity in serum samples collected during the past 2 decades (3-9).In addition, MERS-CoV nucleotide sequences and virus were detected in respiratory swab samples, predominantly from juvenile dromedaries (5,10).Transmission between humans and camels has been described in Qatar and Saudi Arabia (11,12).No autochthonous MERS-CoV infections in humans have been reported in Africa.Most dromedary camels traded in the Middle East are bred in the Greater Horn of Africa, primarily in Ethiopia, Sudan, Somalia, and Kenya (13).To further analyze the spatial and temporal distribution of MERS-CoV-seropositive camels, we tested archived camel serum samples originating in Egypt, Sudan, and Somalia, accumulated during the past 30 years, for MERS-CoV antibodies. The StudyA serum sample from each of 189 dromedary camels was collected by trained personnel as previously described ( 14).Blood samples were taken by jugular vein puncture.The blood was allowed to clot and subsequently centrifuged to obtain serum, or serum was separated from the coagulated blood during slaughter.All serum samples were heat-inactivated at 56°C for 30 min (14).Serum from Somalia was collected during 1983 and 1984; samples from Sudan were collected during June and July 1984, and samples from Egypt were collected during June and July 1997.All camels from Sudan were female (>6 years of age) and belonged to the Anafi breed.They were kept locally and used as a means of transport and a source of milk.The camels from Somalia were sampled at slaughterhouses in Afgoi and Mogadishu.Most camels were adults; however, detailed information about sex and age was not available.The camels from Somalia were bred predominantly for milk and meat.No background information was available for the camels from Egypt.Our study fully complied with national regulations and was approved by the ethics committee of the International Livestock Research Institute accredited by the National Council of Science and Technology in Kenya (approval no.ILRI-IREC2013-12).We tested all serum samples for MERS-CoV antibodies at a 1:100 dilution by a recombinant MERS-CoV spike protein subunit 1-based ELISA (rELISA) as previously described (3,12).To determine the assay-specific cutoff value, we tested 124 confirmed MERS-CoV antibody-negative and 106 MERS-COV antibody-positive camel serum samples from previous studies (3).For inter-assay calibration, we used the same selected positive serum samples in all applications.The optical density (OD) was measured at 450/605 nm.We determined the OD ratio by dividing the OD of each sample by the OD of the positive serum.The cutoff was defined as the 3-fold mean OD ratio of all tested MERS-CoV antibody-negative serum samples (online Technical Appendix Figure 1, http://wwwnc.cdc.