1234 



YELLOW FEVER 



It is also stated that before a stegomyia can lay eggs she must 

 have a feed of blood, the eggs being laid three days later, after which 

 she is said to feed only at night, while before this she feeds during 

 the day and during the night. 



From this it is argued that any stegomyia which bites in the day- 

 time can have only immature parasites, and therefore cannot 

 produce an infection. 



A mosquito can produce yellow fever some fifty-seven days after 

 infection, which appears to become more virulent the longer it 

 remains in the insect, especially if the air temperature is 27° to 28° C. 



Further, the contagium vivum can apparently only exist in man 

 and Stegomyia calopus, though it is true that a chimpanzee, after 

 an incubation of three days, suffered from a typical attack of yellow 

 fever, induced by experimental mosquito-bites, as was shown by 

 Thoriias in 1907. No other mosquito so far has been proved to 

 carry the infection. It appears, also, that the development in the 

 mosquito depends to some extent upon the air temperature, as in 

 the case of the malarial parasite. 



Thomas has succeeded in producing a reaction in a chimpanzee five days 

 after infection by the bite of an infected Stegomyia, and in guinea-pigs from 

 four and a half to thirteen days after being bitten by infected Stegomyia. 

 It must be remembered that in yellow fever epidemics it is stated that dogs 

 and fowls are supposed to be ill, but from what cause is unknown. Manson 

 has suggested that the disease rnay be kept up by animals. 



The aetiology may therefore be summarized by saying that the 

 causation is an animal parasite, living in the blood stream of man 

 and in the body of Stegomyia calopus Meigen, 1818 (S, fasciata 

 Fabricius, 1805, non O. F. Muller, 1764), by the bites of which it can 

 be transmitted to man and the chimpanzee. The blood of the in- 

 fected man is transmissive only during the first three to four days. 

 Stegomyia calopus begins to be infective fourteen days after the 

 transmissive feed, and remains infective for at least another forty- 

 three days, and it has been claimed that it can pass on the infection 

 to its young, which require a feed of blood before the virus becomes 

 infective. During this non-infective period they bite during the 

 daytime, but do not after their first feed and the deposition of their 

 first eggs. It is possible that other species of Stegomyia, in the 

 future, may be found to be carriers as well as 5. calopus. 



Unfortunately, according to Theobald, it is necessary to change the old 

 name Stegomyia fasciata Fabricius, 1805, to 5. frater Desvoidy, 1827, or to 

 5. calopus Meigen, 181 8, though there is some doubt as to whether the latter, 

 which is, of course, the older term, really applies to the insect we know as 

 S. fasciata. The reason for this change is because the term, fasciata was used 

 by O. F. Muller in 1764 (not by de Villers, often wrongly spelt Villiers) for a 

 Culex distinct from 5. fasciata Fabricius, 1805. More recently there seems 

 to be some doubt as to the correctness of the new term — that is, 5. calopus — 

 and a return to the old term, 5. fasciata, may be necessary. 



SpirochcBte. — In 1909 Stimson, reported the presence of a spiro- i 

 chaste in yellow fever (5. interrogans Stimson, 1909), but no im- 

 portance was given to this observation. Recently Noguchi has 

 cultivated from the blood of several cases a spirochsete somewhat 



