BOSTON, Aug. 10— Growing numbers of wild animals in populated areas of the Northeast, the upper Middle West and the Pacific Coast are increasing the number of dangerous tick-borne diseases, a Harvard scientist has warned.
Thousands of cases of Lyme disease, Babesiosis, equine encephalitis and Rocky Mountain spotted fever are now being seen, Dr. Andrew Spielman, professor of tropical public health at the Harvard School of Public Health, said recently. There are also many cases of canine heart worm, which may be transmitted to humans by a mosquito.
''This is an extremely important problem in terms of numbers of people involved,'' he said. ''It causes thousands of cases a year, a small number of deaths and much disability. There's been an increase in transmission in both range and, in particular locations, in intensity.''
Lyme Disease Most Prevalent
The most prevalent is Lyme disease, named for an eastern Connecticut town where an epidemic occured in 1975.
Lyme disease begins with a red area of the skin that enlarges slowly around a darker central portion where the bite occurred. This phase is accompanied by fever, headache, pain in the joints and occasional chills. It also often causes long-term heart problems and arthritis.
Since 1974, when Dr. Spielman identified the tick in Lyme, Conn., he said, it has spread to 14 states in the Northeast, the upper Middle West and the Pacific coast. He said he suspected that migratory birds were responsible for the movement of the ticks into new regions. Lyme disease and Babesiosis are generally caught only between the months of April through early August.
Growth of Animal Population
''Lyme disease has spread rapidly from Massachusetts and Connecticut to other states,'' said a report by the school's in-house publication. ''Babesiosis, an ancient tick-borne scourge of animals and now afflicting humans, is also increasing alarmingly.''
The tick that transmits Lyme disease and Babesiosis is about the size of the head of a pin and spends its adult life on deer. As deer and other animals that carry the ticks increase in numbers and range, the incidence of animal-borne disease is rapidly increasing.
''Raccoons and skunks have become more numerous in the cities of the Northeast,'' the report said. ''Opossums, once seen only in the south, are becoming adapted to New England.
''Even the desert armadillo, host of leprosy, is extending its range into colder and moist regions. The new nonhuman residents of the Northeast threaten to share their pathogens with the human inhabitants.''