MERS Coronavirus Among Dromedary Camels, Africa
MERS Coronavirus Among Dromedary Camels, Africa
Since the discovery of MERS-CoV in 2012, accumulating serologic and molecular evidence demonstrates that the virus in dromedaries is genetically very similar to MERS-CoV in humans and points to the conclusion that dromedary camels are reservoirs for human infection. MERS-CoV genomic fragments have been detected in dromedaries in Qatar and Saudi Arabia; near full-genome sequences have been generated from dromedaries in Egypt and full-genome sequences have been generated from dromedaries in Saudi Arabia. Here, we show serologic evidence for circulation of MERS-CoV or MERS-like CoV in dromedaries in countries in East, West, and North Africa, with possible herd-specific differences in prevalence in Tunisia. The lower seropositivity observed in herds raised for meat production in Tunisia might reflect a high turnover of camels with a continuous introduction of animals unexposed to the MERS-CoV into these herds. No camels imported from neighboring countries were found at the meat-producing farms in Sidi Bouzid and Sousse, only camels purchased from other farms in the same area or other areas in Tunisia. However, animals are frequently moved between Libya and Kebili for trade.
Samples in this study were collected during 2009–2011, confirming observations by us and others that the virus circulated well before March 2012, which is the estimated time of identification of the most common ancestor for the MERS-CoV strains found in humans to date. The earliest serologic indication for circulation of MERS-CoV or MERS-like CoV in dromedaries was observed in 1992; however, this result was based on results of a whole-virus ELISA with undescribed specificity. On the basis of well-validated array and neutralization tests, the study of dromedaries in the United Arab Emirates showed the presence of MERS-CoV or MERS-Cov-like antibodies as early as 2003. The accumulated data on MERS-CoV serology in dromedaries (Figure 2; Table 1) show circulation of MERS-CoV or MERS-like CoV in dromedaries in Africa and the Arabian Peninsula well before 2012, when the first cases in humans were identified, and show overall high levels of seropositivity, including in animals from countries without reported human cases.
(Enlarge Image)
Figure 2.
Geographic distribution of serologic evidence for Middle East respiratory syndrome coronavirus (MERS-CoV) or MERS-like CoV circulation in dromedaries in Africa and the Arabian PeninsulaGray shading indicates countries with seropositive dromedaries; solid black outline indicates countries with primary human cases; dotted outline indicates countries with secondary human cases. For each country with affected dromedaries, the year of sampling, % seropositive, total number tested, and age group are indicated. A, adult, >2 years of age; J, juvenile, ≤2 years of age. Details on serologic tests used and references are in Table 1.
A question raised by these findings is whether human cases occur outside the Arabian Peninsula and if such cases are currently underdiagnosed in Africa. In addition, for the whole region, the possibility exists that MERS-CoV illness occurred before its discovery in 2012 and that such infection has been overlooked in the areas with evidence for virus circulation among animals during the past 10 years. Retrospective studies of cohorts of humans with respiratory illnesses of unknown etiology should address this notion.
Alternative explanations for the lack of cases in Africa could be the following: a different risk profile, for instance, related to demographics and local practices; or subtle genetic differences in the circulating virus strain. Full-genome sequencing, virus isolation, and phenotypic characterization of viruses circulating outside the Arabian Peninsula will resolve this issue. Meanwhile, awareness of MERS-CoV infections should be raised among clinicians in Africa.
Conclusions
Since the discovery of MERS-CoV in 2012, accumulating serologic and molecular evidence demonstrates that the virus in dromedaries is genetically very similar to MERS-CoV in humans and points to the conclusion that dromedary camels are reservoirs for human infection. MERS-CoV genomic fragments have been detected in dromedaries in Qatar and Saudi Arabia; near full-genome sequences have been generated from dromedaries in Egypt and full-genome sequences have been generated from dromedaries in Saudi Arabia. Here, we show serologic evidence for circulation of MERS-CoV or MERS-like CoV in dromedaries in countries in East, West, and North Africa, with possible herd-specific differences in prevalence in Tunisia. The lower seropositivity observed in herds raised for meat production in Tunisia might reflect a high turnover of camels with a continuous introduction of animals unexposed to the MERS-CoV into these herds. No camels imported from neighboring countries were found at the meat-producing farms in Sidi Bouzid and Sousse, only camels purchased from other farms in the same area or other areas in Tunisia. However, animals are frequently moved between Libya and Kebili for trade.
Samples in this study were collected during 2009–2011, confirming observations by us and others that the virus circulated well before March 2012, which is the estimated time of identification of the most common ancestor for the MERS-CoV strains found in humans to date. The earliest serologic indication for circulation of MERS-CoV or MERS-like CoV in dromedaries was observed in 1992; however, this result was based on results of a whole-virus ELISA with undescribed specificity. On the basis of well-validated array and neutralization tests, the study of dromedaries in the United Arab Emirates showed the presence of MERS-CoV or MERS-Cov-like antibodies as early as 2003. The accumulated data on MERS-CoV serology in dromedaries (Figure 2; Table 1) show circulation of MERS-CoV or MERS-like CoV in dromedaries in Africa and the Arabian Peninsula well before 2012, when the first cases in humans were identified, and show overall high levels of seropositivity, including in animals from countries without reported human cases.
(Enlarge Image)
Figure 2.
Geographic distribution of serologic evidence for Middle East respiratory syndrome coronavirus (MERS-CoV) or MERS-like CoV circulation in dromedaries in Africa and the Arabian PeninsulaGray shading indicates countries with seropositive dromedaries; solid black outline indicates countries with primary human cases; dotted outline indicates countries with secondary human cases. For each country with affected dromedaries, the year of sampling, % seropositive, total number tested, and age group are indicated. A, adult, >2 years of age; J, juvenile, ≤2 years of age. Details on serologic tests used and references are in Table 1.
A question raised by these findings is whether human cases occur outside the Arabian Peninsula and if such cases are currently underdiagnosed in Africa. In addition, for the whole region, the possibility exists that MERS-CoV illness occurred before its discovery in 2012 and that such infection has been overlooked in the areas with evidence for virus circulation among animals during the past 10 years. Retrospective studies of cohorts of humans with respiratory illnesses of unknown etiology should address this notion.
Alternative explanations for the lack of cases in Africa could be the following: a different risk profile, for instance, related to demographics and local practices; or subtle genetic differences in the circulating virus strain. Full-genome sequencing, virus isolation, and phenotypic characterization of viruses circulating outside the Arabian Peninsula will resolve this issue. Meanwhile, awareness of MERS-CoV infections should be raised among clinicians in Africa.