NEW YORK -- Scientists, unable to get a good handle on the incidence of Lyme disease in humans, are turning to domestic animals as surrogate indicators of its spread through populated areas of the United States.

Lyme disease, requiring as it does mice and deer to keep the cycle going, is most likely to occur in areas where brush and woodland abound. These are precisely the areas where domestic animals and human beings encounter Lyme-bearing ticks and come down with the disease.

Although Lyme is not known to spread directly from lower animals to humans or vice versa, both can get it from the bite of an infected tick, and both can become very sick.

Thoroughbred race horses and prize-winning show dogs have had to be destroyed because of the ravages of Lyme disease. Cows in Wisconsin dairy herds have also become infected, and while there is no direct evidence that their milk can carry the Lyme germ into the human food supply, the possibility worries public health experts.

Direct testing of large numbers of individual humans' blood for antibodies to Lyme disease -- as has been suggested in the AIDS epidemic -- is regarded as neither cost-effective nor feasible. Moreover, it is possible to get more information more quickly about a chronic disease by studying animals rather than humans because animals do not live as long as people do.