Xl] MODE OF INFECTION I95 



way on the cattle. In India, Martialis has noticed that the 

 cows and horses are sometimes attacked by dengue, often 

 presenting a temporary paralysis of one or more legs, but 

 usually recovering after three or four days. Also, Duchateau, 

 during an epidemic in the Senegal, noticed that it coincided 

 with a high mortality amongst the wild birds and fowls. 



None of these theories has received any support from 

 experiments, for up to the present all attempts to infect 

 animals have remained negative. 



Finally, in 1903, Graham propounded the theory that 

 Culex fatigans is responsible for the transmission of this disease 

 and supported his theory by experiments. Ashburn and 

 Craig, however, are the only investigators who have actually 

 succeeded in transmitting the disease by the bites of infected 

 Culex fatigans. It should be noted, however, that they only 

 succeeded on one occasion and their results have not been 

 confirmed. 



The details of Ashburn and Craig's experiments are as 

 follows : 



On September 12th, a non-immune soldier was placed 

 under a mosquito net with about 20 Culex fatigans that had 

 fed on a dengue patient the previous night. The man was 

 bitten on the night of the 12th, approximately one day after 

 the mosquitoes had fed. About three and a half days later he 

 shewed a distinct rise of temperature and a day later developed 

 a typical attack of dengue. 



It is evident that in this experiment the parasite causing 

 the disease had no time to undergo any cycle of development 

 in the mosquito, except a very short one. As all attempts to 

 infect persons by the bites of mosquitoes after an interval of 

 more than one day gave negative results, Ashburn and Craig 

 are of the opinion that the parasite of dengue is merely capable 

 of living in the stomach of the mosquito and does not need to 

 undergo any cycle of development before becoming infective. 



It must be admitted that the experimental evidence in 

 support of the mosquito transmission theory is very incomplete, 

 but a consideration of its epidemiology leaves no doubt as to 

 the usual mode of infection. 



13—2 



