Follow the map

Another cow disease with a possible link to humans

United StatesOct 8th 2005 edition

CRITICS of America's cattle industry like to claim that its main problem with bovine spongiform encephalopathy (BSE—or mad-cow disease) is refusing to admit that it has a problem. That charge is perhaps even more pertinent when it comes to a lesser known ailment, Mycobacterium avium subspecies paratuberculosis, more commonly known as MAP.

This hardy bacterium has been found in soil and water, and it boasts qualities a cockroach dreams about. It survives extreme temperatures and can lie dormant for months before orally infecting its host. Most often, cows become infected with MAP at birth. If they do, it can develop into Johne's (pronounced Yo-nees), an incurable wasting disease which can reduce beasts to pitiable, diarrhoea-racked skeletal creatures in their last days.

MAP is extremely common: the last big survey, back in 1996, found that one in five dairy herds had the disease, with that proportion doubling among big herds with more than 300 cows. The numbers have probably risen since then. Johne's costs the dairy industry alone $250m a year in lowered production and early cow culling, according to the Agriculture Department.

Left at that, the sickness would probably be just another ghastly farming disease (cattle get anthrax as well). But researchers are investigating whether Johne's is linked to Crohn's disease in humans. The diseases share similar symptoms; Crohn's is an inflammatory bowel disease characterised by chronic, sometimes crippling, diarrhoea. Several scientists suspect that some people may have a genetic susceptibility to developing Crohn's—possibly by drinking milk infected with MAP.

The government and the industry both insist that pasteurisation—heating up milk to a high temperature for a short period—kills any MAP that gets into it. But a recent study of pasteurised whole milk in shops by researchers at Marshfield Clinic Laboratories in Wisconsin found traces of the bug in 2.8% of the samples. This has left the industry in an awkward position: it needs more government money to fight the disease, but kicking up a fuss about it sours milk's wholesome image.

The government officially launched a Johne's control programme three years ago. But the White House is preoccupied by bioterrorism and mad-cow disease: and it wants to trim the budget deficit. The current budget cut next year's allocation for Johne's disease from $19m to $3m.

This reflects the fact that few politicians have heard of Johne's, and the industry seems unsure how much to tell them about a disease which carries a stigma even in the cattle industry. “It's like you have the plague,” admits Jackie Menn, a Wisconsin farmer, whose herd of 85 Jersey cows is infected. Her herd is taking part in a joint federal-state programme to control the disease (which includes culling sick cows). Wisconsin has signed up for the national programme, which is voluntary; but several other cattle states, including Wyoming and Montana, have not.

The biggest problem may lie in California. The average dairy herd there had 806 cows in 2003; some farms boast thousands of animals and they are often kept in close proximity. The state has 55 dairy herds in its control programme, but that leaves another 2,070 to go—and that does not include beef farms.

This article appeared in the United States section of the print edition under the headline "Follow the map"

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