Camel 'plague' puzzles scientists

• Robin McKie, science editor
• The Observer,

A camel lies dead at the side of a road near the Saudi capital Riyadh. Photograph: Issa Abdul Haq/AFP/Getty Images

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 2,000 and 5,000 perished inexplicably, it was revealed in Science last week. The ships of the desert are being sunk in unusual, and worrying, numbers, the journal warned.

'The numbers of deaths we are seeing at present are unprecedented,' said camel researcher Bernard Faye, who is based at the French Agricultural Research Centre for International Development (Cirad). 'A great many animals are dying and it is not at all obvious what is the cause. The problem is that there is a real lack of good epidemiological evidence, and until we can get that we will struggle to find the causes of these deaths and to find ways of stopping them.'

There were several outbreaks of sudden deaths among camels - which are exploited for their milk and meat and as beasts of burden in North Africa and Asia - in many countries last year. However, the worst occurred in Saudi Arabia. At least 2,000 dromedaries perished in a region south of Riyadh, the Saudi capital. Unofficial estimates put the death toll as closer to 5,000.

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 and evidence pinpointing fodder contaminants is disputed by experts. 'Neither mycotoxins nor any known disease could have killed 5,000 camels in that short span of time,' said Ulrich Wernery, scientific director of Dubai's Central Veterinary Research Laboratory.

Camels are associated with hardiness, their ability to survive on small amounts of drinking water and blood-cooling systems that let them work in intense heat. But recently reports of camel deaths across the region have increased dramatically - on top of the Saudi outbreak. Changes in types of fodder may be linked to immune problems, it is suggested. Other scientists argue that climate change may be increasing numbers of disease-bearing insects, while others argue that changes in the use of camels, which are exploited less for transport and more for milk and meat today, may be making them more susceptible to disease.

'It is a puzzle, and until we get more information we are not going to get close to finding an answer,' said Faye.