Field of Science

We should continue to study camels if we care about zoonotic diseases

Dromedarian camel
Inspired by the latest evidence suggesting that camels may have been infected with a close relative of the MERS-CoV (read this from CIDRAP for a nice coverage of the paper) , here's a few top camel facts regarding their relationship with viruses, other wildlife and humans.  Draw your own conclusions from these points.

1) They are found on three continents (Africa, Eurasia and Australia - only here for 150 years) and used to be found on many more (North/South America) but were driven to extinction there probably by climate change or by the actions of humans. Their current wide distribution across the world would allow contact with many other wild (or domestic) animals, and of course this means their viruses. One of the species that camels would undoubtable interact with are humans, but that's because we domesticated them.

They are also found on the Canary islands (brought their by the Moors). Here they are the most important livestock animal and are heavily adapted to that particular environment. This population has been shut off from the other camel populations in Africa for 20 years, so just how is the positive  antibody results explained? Even the canary island bats are unique.

2) Thousands of years (3-6)  ago humans domesticated the camel (Romans used them for military uses). They have been domesticated by humans for food (milk and meat) and work. Oh, and fun. The only wild camel populations left are left are in the Gobi desert. There are feral herds in Australia however. You can milk a camel and get milk and then make cheese or yoghurt. You can see why they would be so popular. Think of them as movable larders. Also, a dead camel is a lot of meat as well and roasted camel has been used for feasts. They are also considered very high value ($250,000 each) and thus their potential worth would probably prevent common slaughtering of the animals.

They are deemed unclean by Islam (however you can easily circumvent this law) and Judaism.

3) They can live until they are 50 - that's a long time if you consider how many infections you pick up over a year. So interpreting antibody evidence may not tell you much. Could this explain the antibodies in Canary island camels?

4) Camel antibodies (single chain 'nanobodies') have interesting properties when compared to human antibodies. This could potentially have implications for immunity to viral infections if you consider how potent they are, their half life or their tissue permeability and hence access to barrier sites.

5) There are a lot of camels out there. Over 14 million to be precise. They show an uneven distribution with the highest concentration is in the horn of Africa, a hot spot of biological diversity, economic disparity and a major trade hub (including with Saudi Arabia - in the past this exchange has already lead to Rift Valley fever epidemics.) . "On an average day, 300-400 heads of goats and sheep, 120-150 heads of cattle and about 50-60 camels are sold," Farah said."  This album speaks volumes.  The kind of place an emerging virus thrives in. Two pictures in this Flickr album highlights why you should watch this area. 1 and 2. This is even more interesting with the discovery of diverse coronaviruses in African bats.

" Cash is received at town markets for male camels sold for slaughter at the age of six to seven years. They are collected at regular intervals into large herds and driven to the meat markets in Egypt, where they bring in profits ranging from LSd 7 000 to LSd 12 000, i.e. approximately US$600 to US$1000, per head. "from wikipedia.

6) They get disease (unlike what we thinks happens with bats) from infections and can pass these on to humans and other animals. There has even been an example of camel to human plague transmission. 

It looks to me that camels are in a fairly rare position of being so numerous and found across so much of the world that they could easily have picked up any number of potentially zoonotic viruses. Even these population densities could even support endemic transmission of camel-adapted viruses. Until MERS-CoV is isolated from camels and shown to be maintained in the populations we should keep this theory in mind that MERS could be a camel-specific virus. The close contact between humans and camels also would facilitate a relative fluid movement of microbes and thus camels could easily act as a amplification host for these kinds of zoonotic viruses. What is worrying is that camel trade and movements between diverse ecologies (tropical central/East Africa and the Middle East) via unique trading hubs could rapidly sample and spread a large swathe of microbial diversity out there, from bats, other mammals or birds. Or even from humans in a reverse zoonosis kind of way. I feel that this antibody work is only a small piece in the MERS puzzle and that camels may act as a virus indicator species in this area of world. If you study camels intensely you may find more viral surprises and could rapidly inform public health policy.

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