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The Cattle Reservoir for Equine Trypanosomiasis in Panama

Additional Notes on the Subject

1. Native cattle of the Republic of Panama can act as an important reservoir for T. hippicum, the cause of equine trypanosomiasis. Our survey methods indicate that the cattle carrier index will range from 2 to 6 per cent where the horse disease is present.

2. Length of the carrier state. Thick blood films will reveal a scant number of trypanosomes from the time of inoculation for about two weeks. The six calves ranged from eleven to eighteen days. One film from calf 2 was positive on a day about six months after its inoculation but there were none positive between the twelfth day and that remote period.
Guinea pig tests show that the six calves failed to infect anywhere from two to six months after they acquired the infection. The complement fixation test applied to four of the calves showed a positive response at the end of six months in three and at the end of nine months in one. The calves were killed and we can not state with certainty when this response might have failed. We know it failed to respond in 16 horses cured of the disease in 1930 to 1931 and tested in August, 1934.

3. The complement fixation test should be of practical use in surveying a herd of cattle for carriers.

4. Physical condition of the calves. The calves grew in a normal manner and were fatter than cattle of a similar age left on the range.

5. The 5 strains of T. hippicum recovered from range cattle were injected into healthy horses. An acute trypanosomiasis developed similar in all respects to the strains formerly recovered from horses.

6. Three vampire bats (Desmodus rotundus murinus) were fed on cattle carriers. One acquired the disease and transferred it to a guinea pig. Two failed to acquire the disease. It is quite evident that the peripheral blood of an animal must contain a fair number of the trypanosomes at the time the bat feeds on it.

Received February 11, 1935.