Attempted Reversal of Filarial Periodicity in Dirofilaria Immitis

Abstract

Since Manson 1 discovered the phenomenon of filarial periodicity in China numerous investigators have sought to elucidate its mechanism. Mackenzie 2 was the first to reverse this periodicity by inverting the period of sleep and activity and his success led him to the belief that the sleeping and waking states are primary factors in its production. Manson successfully repeated and varied Mackenzie's experiment and since then a number of investigators have confirmed it, including Low, Manson-Bahr and Walters. 3 , 4 These workers pointed out, on the basis of very careful 2-hour sampling, that true reversal did not occur but an irregular periodicity resulted from the patient's changing his daily routine.

In an endeavor to shed some light on the mechanism of periodicity an attempt was made to reverse the cycle by changing the daily routine of filaria-infected dogs. Two animals were chosen for this experiment, one with a relatively high number of microfilariae (minimum of 40,000 per cu. cm.) and the other with only one-tenth this number. The animals were placed in separate cages, small enough to prevent much exercise, in a basement room without windows but ventilated by a fan system, run continuously throughout the experiment. Filarial counts were always made in duplicate, using 2 calibrated pipettes, which in the case of the dog with the heavy infection removed 8 cu. mm. of blood and in the one with the lighter infection 20 cu. mm. The blood sample was obtained by cutting the margin of the ear of the dog so that the blood ran freely and after duplicate samples were taken, bleeding was immediately stopped by pressure. It is essential that no clotting occur during the securing of the sample. The thick film technique was utilized for staining.