Key Points:

An unprecedented number of camels across North Africa and the Middle East died last year, researchers have discovered.

The several thousand deaths have baffled scientists who are probing toxins, antibiotic pollution, viruses and even climate change as possible causes.

In Saudi Arabia alone, between 2000 and 5000 perished inexplicably, it was revealed in Science last week.

There were several outbreaks of sudden deaths among camels with the worst occurring in Saudi Arabia. At least 2000 dromedaries perished in a region south of Riyadh, the Saudi capital. Unofficial estimates put the death toll as closer to 5000.

Initial reports blamed infectious disease, but after Saudi vets sent blood samples to international laboratories it was announced that the animals had been killed by contaminants in their fodder.

Two particular contaminants were pinpointed: the antibiotic salinomycin, a supplement used in chicken feed that is toxic to camels, and a fungal species with mycotoxins that can cause nerve damage.

However, the Saudi government has shared little information about its investigation.