A daily chronicle of ongoing events pertaining to infectious diseases
Wednesday, August 28, 2013
ProMED: MERS-COV - EASTERN MEDITERRANEAN (61): ANIMAL RESERVOIR, BAT, COMMENT
Published Date:2013-08-28 Archive Number:20130828.1907567
Date: Tue 27 Aug 2013 Source: European Centre for Disease Prevention and Control (ECDC) - Scientific advice - review, comment [edited] http://tinyurl.com/o88lmlx
MERS-CoV isolated in a bat -------------------------- A study published in the Centers for Disease Control and Prevention journal Emerging Infectious Diseases by Memish et al, analyzed the presence of coronaviruses (including MERS-CoV) in 1003 samples from wild bats collected in October 2012 and April 2013 in Saudi Arabia [see ProMED-mail posting 20130822.1895035]. Samples were collected in Bisha, Saudi Arabia, close to where the 1st patient with MERS-CoV was identified in September 2012 and in other regions where MERS-CoV cases have been found. Multiple alpha and beta coronavirus sequences were identified in 220 out of 732 roost feces samples and 7 of 91 rectal swab samples or fecal pellets. One amplified sequence of MERS-CoV from a _Taphozous perforatus_ bat captured in October 2012 in Bisha matched 100 percent with the MERS-CoV cloned from the index case-patient in Bisha.
The authors conclude that bats might play a role in human infection although this does not exclude the possibility of other hosts.
ECDC comment, 26 Aug 2013 ------------------------- Identifying the host/s and source of MERS-CoV is urgently needed to prevent further infections and spread of the disease. Bat species are a well-known reservoir of coronaviruses and the study of Memish et al confirms this.
While the results from the study are intriguing, there are several limitations that might limit a conclusion that bats are the direct source of MERS-CoV in humans. In this study a total of 1003 different samples were collected from 110 bats captured during 2 samplings (October 2012 and April 2013); of those 227 samples tested positive for coronavirus, only one was found positive for the human MERS-CoV. The information about the viral load of the MERS-CoV positive sample is missing and the failure of further sequencing might lead to the speculation of a very low virus load in the sample. The amplified bat MERS-CoV sequence was very short and lies within a conserved region of the genome, however a divergence within other genomic regions cannot be ruled out. Furthermore the MERS-CoV sequence amplification product of this positive sample was retrieved only from newly established generic MERS-Coronavirus (nested RdRp) assay, while the World Health Organization recommended MERS-CoV specific assays were negative.
All coronavirus sequences were detected in fecal pellets or from roost feces but not from serum, throat swab samples, or urine. It is unclear if other samples from this particular MERS-CoV positive animal were also available and tested in this study. The possibility of transmitting virus via faeces from bats to humans has been discussed for rabies (Gibbons 2002, Johnson, Phillpotts et al 2006) and might also been a route of transmission for MERS-CoV. Just as people have been infected with hantavirus while sweeping-up dried mouse droppings humans (and camels) could be infected by inhaling dust mixed with dried contaminated bat, or other animal, excrement (Jonsson, Figueiredo et al 2010, Richardson, Kuenzi et al 2013).
This, and the study of Reusken et al (Reusken, Haagmans et al 2013) cited in the ECDC Public Health Development of 12 Aug 2013 (http://tinyurl.com/pgfja9a) provide evidence that MERS-CoV might be a zoonotic disease but it is still not clear how the disease progresses from animals to humans. The epidemiological investigations excluded so far direct animal contact of most of the MERS-CoV patients as the probable route of infection but indirect mechanisms could be involved.
The previously published ECDC risk assessment is still valid.
[In case bats are eventually shown convincingly to play a role in the epidemiology of MERS-CoV as a virus reservoir, the route by which humans get infected is still to be clarified. One hypothesis, cited by ECDC, is infection by inhaling dust mixed with dried contaminated bat, or other animal, excrement.
Involvement of other animal species within the cycle, as well as other routes (such as contaminated food) are still to be excluded. In addition to camels, which have already been subject to some investigation with serological findings, other potential species, including sheep, goats, cattle, and cats, are to be addressed. According to previous reports, such animals have been sampled earlier in Saudi Arabia but no information on the tests -- in case performed -- has become available.
[The essence of this research is that out of a total of 1003 different samples collected from 110 bats captured over a 2-year period, 227 samples tested positive for bat coronavirus sequences, but only one, the latter, was positive for MERS-CoV infection. Information about the abundance of the MERS-CoV sequence in this sample is lacking. The amplified bat MERS-CoV sequence was very short and lies within a highly conserved region of the genome. Consequently, sequence divergence in other regions of the genome cannot be discounted. From the data available it could equally well be concluded that the human victims, and this particle bat, were infected from a similar source, such as an insect or arachnid vector for example. The fact that the MERS-CoV sequences were detected only in faecal pellets or from faeces in roosts, and not from serum, throat swab samples, or urine, would favour such an interpretation. Nonetheless, these findings cannot be ignored and further supportive evidence is awaited. - Mod.CP]