53 



24. Probable Effect of Anti-Mosquito Measures on 

 Mosquito-borne Disease. Yellow fever consists of a 

 single illness followed by more or less immunity from sub- 

 sequent attacks. Hence we may expect that the disease 

 will immediately disappear in a given town as soon as we 

 extirpate the mosquitoes there ; and this has actually 

 happened in Havana, where the chief sanitary officer, 

 Major GORGAS, reports that the disease has been practically 

 stamped out as the result of the vigorous campaign against 

 mosquitoes.* 



But the case will be somewhat different with elephan- 

 tiasis and malarial fever. Both these diseases are lingering 

 ones, in which the parasites remain alive for years after the 

 first moment of introduction by the mosquito. In malaria, 

 relapses continue for a very long time after the patient has 

 removed to a completely healthy climate, such as that of 

 Britain. Elephantiasis is a permanent disease due to 

 mischief caused by the parasite. It is obvious, then, that 

 even after we destroy all the infective agents in a town, 

 still people who became infected before we took this action 

 will continue to suffer from elephantiasis, and from relapses 

 of malaria, long afterwards. In other words, while yellow 

 fever will die out at once, malaria and elephantiasis will 

 die out much more slowly. Hence the extirpation of mos- 

 quitoes will not produce as sudden and marked an effect 

 on the two latter diseases as on the first Indeed, except 

 in the case of newcomers and children born after the 

 operation, not much effect is likely to be manifest in the 

 case of malaria under several years, and in the case of 

 elephantiasis under many years (that is, until the majority 



* Report for September, 1901 Appendix. 



