Studies on Transmission of Experimental Yellow Fevery by Mosquitoes other than Aëdes
Cornelius B. Philip
From the West Africa Yellow Fever Commission of the International Health Division, Rockefeller Foundation, Lagos, Nigeria
1. Experiments with Taeniorhynchus (Mansonioides) africanusTheo. showed that this species is capable of acting in the capacityof insect host for the yellow fever virus. Transmission to monkeyswas accomplished in ten instances with eight fatalities, bothby the bites of mosquitoes and by the injection of their ground-upbodies. Five of the deaths resulted from the inoculation ofground-up insects, and three from infection by bites. A recoveryalso occurred after each method of exposure. One insect wassufficient to cause typical fatal infection.
2. Similar experimentswith Anopheles gambiae Giles (= costalisLw.) failed to produceinfection in test animals through bitesor by injection of theground-up insects after a period equivalentto that requiredby A. aegypti to become infective by bite.
3. To test thepersistence of the virus in A. gambiae, injectionsof theirground-up bodies were made on alternate days afterthey hadfed on infected animals. Fatalities occurred, afterlengthenedincubation periods in the test monkeys, after thetwo and four-dayinjections in one experiment in which unitsof 5 insects wereused each time. In the other experiment, asevere immunizingfever developed following the inoculationof 10 insects twenty-fourhours after their initial blood-meal.Injections after longerintervals were negative, all animalslater proving susceptible.
4. Attempts to determine the incubation period of the virusin T. africanus failed because of an apparently low percentageof infection among the insects, the shortest positive transmissionby biting occurring at sixteen days. Parallel tests with controllosts of A. aegypti in small numbers proved positive in eightdays twice and in nine days once from the time of the originalfeeding.
5. It appears that A. gambiae is not concerned inyellow fevertransmission in West Africa. On the other hand,T. africanusmust be definitely considered in the developmentof a controlcampaign for this disease, as it is an importantdomestic mosquitoin the adult stage, biting humans readily,and is capable ofproducing an experimental infection similarto that producedin M. rhesus by the normal insect host, A.aegypti.