Evaluation of serological assays available in a biosafety level 2 laboratory and their application for survey of Middle East respiratory syndrome coronavirus among livestock in Ethiopia

TERAMICHI, Takurou; FUKUSHI, Shuetsu; HACHIYA, Yuma; MELAKU, Simenew Keskes; OGUMA, Keisuke; SENTSUI, Hiroshi

All camel sera that were positive in any one of the tests-the S1-ELISA, cELISA, or neutralization tests using live MERS-CoV-were positive in the neutralization test using VSV-MERS/GFP. One cow serum was positive for cELISA and another cow was positive in the neutralization test using VSV-MERS/GFP, but negative in all other tests. Because the neutralization test using live MERS-CoV is considered the most accurate serological test and because the two positive reactions were observed in only one serological test among the four, these two bovine sera should be considered as nonspecific reactors. The exact reason of nonspecific reaction of these sera remains unclear. The nonspecific reaction may result from differences in immunological conditions of animals or in the degree of hemolysis during the preparation of samples. For example, a nonspecific reaction sometimes appears in cattle after injection with a certain inactivated vaccine in the ELISA kit for Johne's disease diagnosis in Japan. Some rhabdovirus cross react with VSV [6] and such a virus might be subclinically infected in Ethiopian cattle. There are reports that MERS-CoV specific antibodies were not detected in sera from cattle, goat and sheep in Jordan and Saudi Arabia, the MERS-CoV prevalence region [11, 13] . However, they were kept indoor or did not share the pastureland. Present results indicate that MERS-CoV infects only dromedary camels and is unlikely to infect other domestic animals even sharing the pastureland. Since the antibody positive rate and antibody titer of MERS increased with age, it is considered that MERS-CoV establishes an infection cycle and inapparently present only among dromedary camels [11] . In present studies, the limited numbers of samples were tested because the import of animal sera from the foot-and-mouth disease endemic region is regulated in Japan. Further studies using additional samples from other countries would be required to clarify the role of other animal on the ecology and epidemiology of MERS-CoV.