Thursday, February 26, 2015

Deconstructing the 90% Of Camels Have MERS Meme

Photo: ©FAO/Ami Vitale

Credit FAO


# 9757


Earlier this week a big story hit the Arabic press – and has caused heavy (and very concerned)  traffic on Arabic Twitter – stating that 90% of Saudi Camels have the MERS virus.  I mentioned it briefly two days ago in Postcards From The MERS Twitterverse, but have been unable to find any paper, or study to back up this assertion. 


First a media report on this story, after which I’ll be back with reasons why I think this report is off base.


Almost all Gulf camels have MERS, warns Saudi health official

By Courtney Trenwith

Wednesday, 25 February 2015 1:50 PM

Almost all camels in the Gulf are infected with the Middle East Respiratory Syndrome (MERS), a Saudi Health Ministry official has been reported as saying.

The fatal virus, which already has infected more than 1000 and killed at least 376 patients, is believed to have spread from camels to humans.

The high rate of camel infection – 90 percent, according to Saudi Arabia’s undersecretary for preventative health Abdullah Asiri – raises a serious issue for the Gulf, where camels are a deep part of daily life for many locals.

Asiri said exterminating the animals was not an acceptable solution and instead research on a vaccine needed to be accelerated, Arab News reported.

(Continue . . . )

Obviously, if 90% of Saudi Camels are actively infected, this would pose major infectious disease risk. 


But it is makes far more sense that 90% of Saudi Camels have been infected with the MERS coronavirus (i.e. have serum antibodies) sometime in the past. Not that 90% are currently infected (and capable of spreading the disease) as intimated by this report.

It is a small, but important difference.


The idea that camels are a repository for the MERS coronavirus gained traction in August of 2013 when we saw a study in the  Lancet: Camels Found With Antibodies To MERS-CoV-Like Virus, which found specific antibodies to the MERS coronavirus in all 50 (100%) of the dromedary camel samples gathered (from multiple locations) in Oman.


Much lower levels of antibodies were detected in 14% of camels from two dromedary herds tested from the Canary Islands.


The following January (2014) in EID Journal: MERS-Like Antibodies In Camels, UAE 2003-2013, we saw a report showing  97% of  dromedary camel serum samples collected in 2003 and 2013 in the United Arab Emirates (UAE) showed specific antibodies for the MERS coronavirus.


Again in August, in EID Journal: Three Decades Of MERS-CoV Antibodies In Camels, we saw serological evidence showing an infection rate of 81%  going back over 30 years.


But none of these studies were designed to show that these camels were actively infected and shedding the virus.


While we’ve limited reports from the field on active infection with MERS virus in camels, we’ve one study that found 10 of 35 (27%) camels tested during the 2013–14 calving season (see EID Journal: MERS Coronavirus In A Saudi Dromedary Herd) actively shedding the virus. From the report:


At farm A, we detected MERS-CoV in 1 of 4 dromedaries sampled on November 30, none of 11 sampled on December 4, nine of 11 sampled on December 30, and none of 9 sampled on February 14 (Table 1). Of the 10 dromedaries that tested positive for MERS-CoV, 9 had parallel nasal and fecal specimens tested, with virus detected in the nasal swab specimens from 8 and the fecal specimen from 1.

At the December 30 sampling, 7 of 8 calves and 2 of 3 adults tested positive for MERS-CoV, indicating that when MERS-CoV circulates on a farm, both calves and adults can be infected (Technical Appendix[PDF - 81 KB - 3 pages] Table). Because all 12 adults with serum collected before December 30 were seropositive (titers >320), it is likely, though not certain, that the MERS-CoV infections in the 2 adults (nos. 21, 19Dam) sampled on December 30 were reinfections, as has been reported for other CoVs.


And last year (see EID Journal: MERS Coronaviruses in Dromedary Camels, Egypt) we saw a sampling from Egypt that found  4 (3.6%) of nasal swabs (out of 110 tested) were positive for the MERS-CoV virus (via RT-PCR testing). A positive PCR test is indicative of a current infection, with active viral shedding.


Obviously nowhere near the 90% range.


Perhaps even more on point, in EID Journal: Replication & Shedding Of MERS-CoV In Inoculated Camels we saw a study showing that camels intentionally inoculated with the human MERS strain shed copious amounts of the virus via nasal discharge for at least a week.


While there is some evidence that a camel can become re-infected with the MERS coronavirus, we don’t know how often that really happens.  But whether the first infection, or a subsequent one, the `window’ of opportunity for passing on the virus to humans (or other camels) appears limited to a week or two. 

As young camels have the least exposure to the virus, they appear the most susceptible to infection. And that has been postulated as a factor in the spring surge of MERS infections across the Middle East.

Camels appear to be an important conduit for the virus to move into the human population, but we’ve seen estimates that only 3% of cases are caused by direct zoonotic infection (see Dr. Tariq Madani: 97% Of MERS Cases From Human-to-Human Transmission).

If camel-to-human transmission could be eliminated, it might stop the reseeding of the virus into the human population. 


And until a camel vaccine can be developed, and deployed, exercising caution and good infection control practices around camels is certainly advisable.

But as far as the claim that 90% of camels have MERS, that appears to be more than a little overstated.

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