Camels are like edible cargo vans, as useful for their sturdy backs as for their milk and meat. But a new study by Iranian researchers suggests the health of that country's fleet is in jeopardy.

Nearly 84 percent of male camels in eastern Iran may be infected with helminths (parasitic worms) that can cripple reproduction and afflict other organs, the scientists report in the journal Parasitology Research. The mosquito-borne helminths, Dipetalonema evansi, have long been known to beset camels and other species of livestock.

The latest finding, however, is the most thorough estimate of their prevalence in Iranian camels, a key stock species in that country. The parasites can cause filariasis, a disease that infects both sexes of a host species but is particularly destructive to the male genitalia, causing often grotesque deformities of the testes.

The researchers looked for evidence of D. evansi in samples of blood and tissue from 1,070 dromedaries—camels with a single hump—slaughtered for meat between 2003 and 2006. Blood tests from more than one fifth of the animals showed signs of infection with the worms; further study revealed that 83.7 percent of the male camels had parasites in their lungs and reproductive organs.

"The high prevalence rate of this infection surprised me," says Ahmad Oryan, professor of veterinary pathology at Shiraz University in Iran, who led the research. "Due to the effects of this nematode [a type of roundworm] on breeding of the male camels, this infection, if not treated or controlled, could have adverse outcomes and will affect the calving rate of this animal."

D. evansi had previously been found in camels from southern and central Iran by Oryan and others. "It seems this infection is reported in most areas of this country that normally rear camels," he says.

Saudi Arabia's camel population has been severely hurt by a mysterious die-off that has claimed thousands of animals over the past year. The cause of those deaths is unknown, with theories ranging from viral infections to toxic chemicals in camel feed, but Oryan says filariasis probably is not to blame.

"This disease will affect the fertility of male animals, but the rate of mortality due to this disease is low and no clinical symptoms are present in the low-infected camels," he says. "So we cannot correlate the deaths of the camels in Saudi Arabia to this disease."

The U.N. puts the world's camel population at about 20 million. That number has been falling in many countries, as camels are increasingly used for food rather than as "ships of the desert". The recent surge in oil prices, however, has been a boon to camels, making them an economical alternative to trucks and tractors for transporting cargo. In Iran, at least, endemic filariasis among the creatures "constitutes an important health problem to camels in this area," the study authors wrote, "resulting in high morbidity, impaired working capacity and lowered productivity."