The resistance to re-infection of cats repeatedly inoculated with infective larvae of Brugia pahangi.

Seven microfilaraemic and five amicrofilaraemic cats which had been repeatedly infected with Brugia pahangi were challenged along with normal cats 28, 14 and 1 day before autopsy. The lymphatics of the amicrofilaraemic cats contained no female adult worms originating from the repeat infections and only two adult males (both from the same cat). Only 5.2% of the worms in the control cats were recovered from the amicrofilaraemic cats. Most of the challenge worms were killed in the first 24 h. The microfilaraemic cats all contained fertile adult male and female worms derived from the repeated infection but in such low numbers as to indicate considerable resistance to infection. Compared to their controls 26.4% of the challenge worms were recovered. Analysis of the life-cycle stages recovered showed that in both groups there was attrition of all stages and that although a number of worms reached L5 these were all killed later in the amicrofilaraemic cats.