Thursday, November 21, 2013

ProMED: MERS-CoV - Eastern Mediterranean (89): animal reservoir, camel susp

Published Date: 2013-11-19 17:24:58
Archive Number: 20131119.2064239
Date: Mon 18 Nov 2013
Source: CIDRAP [summarised, edited]
http://www.cidrap.umn.edu/news-perspective/2013/11/who-confirms-kuwaits-mers-cases-spain-cites-new-case


The World Organisation for Animal Health (OIE) said on [15 Nov 2013] that there was still no convincing evidence that camels are a source of MERS-CoV infections in humans, despite recent findings pointing in that direction. "Currently, there is no strong evidence to consider that camels are a source of infection for human cases of MERS," the OIE said in an update of its questions and answers about the virus.

In serologic studies reported in recent months, camels in Egypt, Oman, and the Canary Islands were found to have antibodies to MERS-CoV or a closely related virus. Further, last week, Saudi health officials reported finding the virus in a sick camel that belongs to a 43 year old case-patient from Jeddah.

Saudi officials said the camel tested positive for the virus by polymerase chain reaction. They said they were sequencing the genomes of the camel and patient's isolates to see whether they match; the results have not yet been reported.

The OIE statement focused on the serologic findings and did not refer to the report of the infected camel. "Currently, there is no strong evidence to consider that camels are a source of infection for human cases of MERS," the statement said. "Based on available epidemiological data, it is difficult to explain the relationship between positive serological results in camels and cases of human infections with MERS CoV.

"Indeed, to date, there is no potential similarity between the strain of MERS CoV isolated in humans and the suspicions shown in camels. It is important to remain open minded about all potential sources of exposure for human cases until more information is available."

The agency went on to say that, thanks to cross-reactivity, serologic tests may not distinguish between antibodies to different viruses that have genetic or antigenic similarities. "Serology tests for MERS CoV have not yet been validated in animals and may not be reliable," the OIE added. "If these tests, which may not be sufficiently specific, are used in animals, there is a risk that 'false positive' results will occur because it may not be possible to differentiate antibodies to MERS CoV from antibodies to other coronaviruses, commonly found in animals. This is why tests in animal should focus on isolating and identifying the virus itself," the agency said.

The OIE voiced a similar view back in July [2013] in an earlier version of the question-and-answer statement. At that point, there were no reports of serologic or virologic findings pointing to camels as a source of the virus, but at least one MERS patient had been reported to have had contact with a sick camel before he got sick.

[byline: Robert Roos]

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[OIE's "Questions and Answers MERS coronavirus (CoV)," updated on 15 Nov 2013, are available at http://www.oie.int/for-the-media/press-releases/detail/article/questions-and-answers-mers-coronavirus-cov/.

The following 2 passages may be of particular interest:

"1. What about serological tests in animals?

Serology tests aim to detect antibodies produced by the animal against the virus and not to search for the presence of the virus itself. Often, it is difficult and sometimes impossible to distinguish antibodies to different viruses having genetic or antigenic similarities, due to what is known as serological 'cross reactivity'.

Serology tests for MERS CoV have not yet been validated in animals and may not be reliable. If these tests, which may not be sufficiently specific, are used in animals, there is a risk that 'false positive' results will occur because it may not be possible to differentiate antibodies to MERS CoV from antibodies to other coronaviruses, commonly found in animals.

That is why tests in animals should focus on isolating and identifying the virus itself.

2. What would happen if MERS CoV is identified in animals?

If information from public health investigations identifies a possible animal source, OIE will support further joint investigations.

OIE Member Countries would be obliged to report a confirmed case of MERS CoV in animals to OIE, as an 'emerging disease' in accordance with article 1.1.3 of the OIE Terrestrial Animal Health Code. If MERS CoV was identified in an animal, this would not necessarily mean that the animal is a source of human infection. Detailed investigations would then be needed to understand the relationship between any animal cases and human cases and whether a finding in animals would be significant for human infection."

On 12 Nov 2013, Saudi Arabia's Ministry of Health notified the 1st time that a camel related to a human case tested positive for MERS-CoV by PCR (posting 20131112.2051424). Reportedly, further testing was ongoing to sequence the patient and the camel virus and compare genetic similarity levels to conclude causality. The results of these tests are not yet available.

If the camel strain is found homologous to the human strain, OIE's requirements, as spelled out above, will have to be fulfilled, namely notification of the case as an 'emerging disease'. In the meantime, precautionary measures, including the isolation of in-contact animals on the suspected farm, have been undertaken by the Saudi authorities (posting 20131113.2053932).

For a recent response from neighbouring Dubai, see http://gulfnews.com/news/world/usa/mers-link-to-camels-opens-a-pandora-s-box-1.1255185. - Mod.AS

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