MERS-CoV in Africa—an enigma with relevance to COVID-19
Authors: Stanley Perlman, Alimuddin Zumla
Journal: The Lancet Infectious Diseases (2020)

Three novel zoonotic coronaviruses that have jumped the species barrier and caused lethal disease in humans have focused global public health attention in the past two decades: severe acute respiratory syndrome coronavirus (SARS-CoV) in 2003, Middle East respiratory syndrome coronavirus (MERS-CoV) in 2012,1Memish ZA Perlman S Van Kerkhove MD Zumla A Middle East respiratory syndrome.Lancet. 2020; 395: 1063-1077Summary Full Text Full Text PDF PubMed Scopus (301) Google Scholar and SARS-CoV-2 in late December 20192—the cause of the ongoing COVID-19 pandemic.2Perlman S Another decade, another coronavirus.N Engl J Med. 2020; 382: 760-762Crossref PubMed Scopus (600) Google Scholar All these coronaviruses are featured in the WHO Blueprint list of priority pathogens for research and development, because they threaten global health security, they have epidemic potential, and there are no effective treatments or vaccines.3WHOPrioritizing diseases for research and development in emergency contexts. World Health Organization, 2020https://www.who.int/activities/prioritizing-diseases-for-research-and-development-in-emergency-contextsDate accessed: June 27, 2020Google Scholar In Africa, only SARS-CoV-2 has caused significant outbreaks and disruption to health services. While African governments implement national mitigation and containment strategies4Nachega JB Grimwood A Mahomed H et al.From easing lockdowns to scaling-up community-based COVID-19 screening, testing, and contact tracing in Africa—shared approaches, innovations, and challenges to minimize morbidity and mortality.Clin Infect Dis. 2020; (published online May 31.)https://doi.org/10.1093/cid/ciaa695Crossref Scopus (48) Google Scholar to control the spread of COVID-19, MERS-CoV continues to circulate in the Middle East causing intermittent outbreaks with up to 34% mortality.1Memish ZA Perlman S Van Kerkhove MD Zumla A Middle East respiratory syndrome.Lancet. 2020; 395: 1063-1077Summary Full Text Full Text PDF PubMed Scopus (301) Google Scholar MERS-CoV is highly prevalent in dromedary camels on the Arabian peninsula and, they are the main sources of primary human MERS-CoV infections.5El-Kafrawy SA Corman VM Tolah AM et al.Enzootic patterns of Middle East respiratory syndrome coronavirus in imported African and local Arabian dromedary camels: a prospective genomic study.Lancet Planet Health. 2019; 3: e521-e528Summary Full Text Full Text PDF PubMed Scopus (45) Google Scholar However, there have not been any reported clinical cases from Africa of confirmed human MERS, despite 70% of the world's dromedaries residing in Africa (with high MERS-CoV infection rates) and frequent occupational and domestic contact between dromedaries and humans.6Farag E Sikkema RS Mohamedani AA et al.MERS-CoV in camels but not camel handlers, Sudan, 2015 and 2017.Emerg Infect Dis. 2019; 25: 2333-2335Crossref PubMed Scopus (21) Google Scholar Little serological evidence of human infection exists.7Ka Pun Mok C Zhu A Zhao J et al.T-cell responses to MERS coronavirus infection in people with occupational exposure to dromedary camels in Nigeria: an observational cohort study.Lancet Infect Dis. 2020; (published online Oct 6.)https://doi.org/10.1016/S1473-3099(20)30599-5Google Scholar, 8Zhao J Alshukairi AN Baharoon SA et al.Recovery from the Middle East respiratory syndrome is associated with antibody and T-cell responses.Sci Immunol. 2017; 2aan5393Crossref Scopus (211) Google Scholar This anomalous disparity between human MERS-CoV infections in the Arabian peninsula and Africa has not been easily explained and there has been a longstanding need for further studies of MERS-CoV at the animal–human interface. In The Lancet Infectious Diseases, Chris Ka Pub Mok and colleagues7Ka Pun Mok C Zhu A Zhao J et al.T-cell responses to MERS coronavirus infection in people with occupational exposure to dromedary camels in Nigeria: an observational cohort study.Lancet Infect Dis. 2020; (published online Oct 6.)https://doi.org/10.1016/S1473-3099(20)30599-5Google Scholar present data that indicate that human MERS-CoV infection is an occupational hazard in dromedary abattoir workers in Nigeria. They focus our attention on the potential for MERS-CoV transmission and human infection and consequent threat to people living in Africa and to public health services. Their observational cohort study of people working at a slaughterhouse in Kano, Nigeria, identified MERS-CoV-specific CD4+ or CD8+ T cells in PBMCs obtained from 61 workers with close contact to dromedaries, but not in 20 other workers from the same slaughterhouse with no dromedary contact. These results agree with others showing that MERS-CoV virus-specific T-cell responses are more sensitive than serological tests for detecting past infection.8Zhao J Alshukairi AN Baharoon SA et al.Recovery from the Middle East respiratory syndrome is associated with antibody and T-cell responses.Sci Immunol. 2017; 2aan5393Crossref Scopus (211) Google Scholar Thus, zoonotic MERS-CoV infections of dromedary-exposed individuals are probably taking place in Nigeria, and, by extrapolation, the incidence of human MERS infections in all regions of Africa with dromedaries has probably been underestimated. Further studies are required to determine the extent of human MERS-CoV infections across Africa. Genetic and phenotypic differences in west African viruses might also be relevant to zoonotic outbreak potential. The great diversity of MERS-CoV lineages, and the large number of MERS-CoV infected dromedaries in Africa,5El-Kafrawy SA Corman VM Tolah AM et al.Enzootic patterns of Middle East respiratory syndrome coronavirus in imported African and local Arabian dromedary camels: a prospective genomic study.Lancet Planet Health. 2019; 3: e521-e528Summary Full Text Full Text PDF PubMed Scopus (45) Google Scholar might, with time, lead to MERS-CoV adapting and transmitting more efficiently, with epidemic potential. The findings of Ka Pub Mok and colleagues7Ka Pun Mok C Zhu A Zhao J et al.T-cell responses to MERS coronavirus infection in people with occupational exposure to dromedary camels in Nigeria: an observational cohort study.Lancet Infect Dis. 2020; (published online Oct 6.)https://doi.org/10.1016/S1473-3099(20)30599-5Google Scholar also have implications for ongoing efforts on COVID-19 diagnostics development, testing, and tracing in Africa and for vaccine development in general.4Nachega JB Grimwood A Mahomed H et al.From easing lockdowns to scaling-up community-based COVID-19 screening, testing, and contact tracing in Africa—shared approaches, innovations, and challenges to minimize morbidity and mortality.Clin Infect Dis. 2020; (published online May 31.)https://doi.org/10.1093/cid/ciaa695Crossref Scopus (48) Google Scholar Mild cases of MERS and COVID-19 induce antibody responses that are transient or wane rapidly.8Zhao J Alshukairi AN Baharoon SA et al.Recovery from the Middle East respiratory syndrome is associated with antibody and T-cell responses.Sci Immunol. 2017; 2aan5393Crossref Scopus (211) Google Scholar Specific diagnostic tests for MERS-CoV and SARS-CoV-2 infected individuals based on relevant antigen-specific CD4+ or CD8+ T-cell responses could allow for more sensitive detection of past or present infection than serological tests and identify additional human MERS and COVID-19 cases. T-cell responses appear to be more stable and useful for detection of previous infection or vaccine response in settings where virus-specific antibody titres are absent. It would also be interesting to know if dromedary-exposed workers with MERS-CoV-specific T-cell responses are protected from developing severe MERS on rechallenge, and by extrapolation, whether T-cell responses are protective against severe COVID-19 disease, even if virus-specific antibody is not detectable. To confirm these results, these studies should be repeated at other sites in Africa and with larger numbers of samples. Furthermore, no MERS-specific T-cell responses were detected in abattoir workers with no dromedary exposure. By contrast, low numbers of SARS-CoV-2-specific T cells have been detected in uninfected individuals.9Grifoni A Weiskopf D Ramirez SI et al.Targets of T cell responses to SARS-CoV-2 coronavirus in humans with COVID-19 disease and unexposed individuals.Cell. 2020; 181: 1489-1501Summary Full Text Full Text PDF PubMed Scopus (2526) Google Scholar These apparent differences in pre-existing immunity to the two coronaviruses are unexpected and need to be reconciled. The results also suggest that COVID-19 and MERS vaccines should be formulated to induce T-cell responses to maximise the likelihood of long-term protection. COVID-19 and MERS provide unique opportunities for African and Middle Eastern countries with relevant stakeholders to align and synergise ongoing COVID-19 and MERS surveillance, diagnostics, vaccine development, and evaluation, with basic science and translational research activities.1Memish ZA Perlman S Van Kerkhove MD Zumla A Middle East respiratory syndrome.Lancet. 2020; 395: 1063-1077Summary Full Text Full Text PDF PubMed Scopus (301) Google Scholar, 10Perlman S Azhar EI Memish ZA Hui DS Zumla A Confronting the persisting threat of the Middle East respiratory syndrome to global health security.Lancet Infect Dis. 2020; 20: 158-160Summary Full Text Full Text PDF PubMed Scopus (6) Google Scholar African and Middle Eastern countries must invest more in surveillance and urgent priority research to fill major knowledge gaps in the epidemiology, transmission, pathogenesis, and evolution of MERS-CoV and SARS-CoV-2, especially because they are co-circulating. The need for an effective One Human-Environmental-Animal Health multidisciplinary consortium across Africa, Middle East, and Asia to tackle the ever-present threat of lethal coronaviruses and other emerging infections remains a global priority.10Perlman S Azhar EI Memish ZA Hui DS Zumla A Confronting the persisting threat of the Middle East respiratory syndrome to global health security.Lancet Infect Dis. 2020; 20: 158-160Summary Full Text Full Text PDF PubMed Scopus (6) Google Scholar We have a special interest in coronaviruses and infectious diseases with epidemic potential. We declare no competing interests. T-cell responses to MERS coronavirus infection in people with occupational exposure to dromedary camels in Nigeria: an observational cohort studyZoonotic infection of dromedary-exposed individuals is taking place in Nigeria and suggests that the extent of MERS-CoV infections in Africa is underestimated. MERS-CoV could therefore adapt to human transmission in Africa rather than the Arabian Peninsula, where attention is currently focused. Full-Text PDF