Australia and yellow fever.

Date:
[1915?]
Catalogue details

Licence: Public Domain Mark

Credit: Australia and yellow fever. Source: Wellcome Collection.

    31/124 (page 21)
    as possible that certain other allied species of mosquito will so act until the contrary has been proved. The Yellow Fever Bureau Bulletin directs attention to this aspect, as follows (42) :— In view of the fact that Stegomyia fasciata has never been proved to be the only mosquito capable of transmitting yellow fever, it would be very interesting to know whether yellow fever cases are ever observed where Stegomyia fasciata cannot be found, and whether in such cases other mosquitoes, especially other species of Stegomyia, are found. The transmission of infection by the Stegomyia (or other) mosquito is not, however, a haphazard one, but is subjcct to certain limiting factors. For example, in the present state of knowledge on the subject, it must be stated that the person already ill with yellow fever must be bitten by the mosquito during the first three days of his illness, in order that the mosquito may be a source of danger to others. In other words, numerous susceptible mosquitoes may bite a yellow fever patient after the first three days of the illness without becoming able to infect any other person. It has been said that this is the present state of knowledge on the subject, and the same must be said regarding the widely accepted idea that a mosquito after sucking blood from a person suffering from yellow fever does not become infective for another person until twelve days have elapsed. This must be accepted at the present time, but it may become necessary to modify this idea later on. The position in this regard is reviewed by Seidelin (43) :— That yellow fever is transmitted in nature by no other means than by mosquitoes has never been proved, but is extremely probable in view of our knowledge of protozoal diseases. The yellow fever germ is supposed to undergo a development in the mosquito of twelve days’ duration. This is made probable by the negative results of experiment in which a period of less than twelve days had elapsed after the mosquito had sucked blood from an infected patient, until it was allowed to bite a non-immune individual. This theory corresponds well with the observations of Carter and others on the extrinsic incubation period, and is likely to be correct, but cannot be considered conclusively proved, as the negative experiments referred to were not numerous and, on the other hand, there is a comparatively large number of negative results in cases in which all conditions for obtaining positive results were fulfilled. Yellow fever blood is considered infectious during the first three days of the disease only, but on very scanty evidence, as I have previously pointed out. My argument has been objected to, but not shown to be erroneous, and I must again assert emphatically that we here have to do with a theory which is without adequate foundation, The negative experiments of the Army Commission prove nothing in this respect. In Carroll’s table of twenty-two cases, with thirty-two negative inoculations, we find two inoculations only in which the patient bitten was in a later period than the third day, whilst the interval allowed in the mosquito was more than twelve days (thirteen and fourteen respectively). In ten inoculations, both conditions for favorable results were fulfilled (patient bitten during first three days of disease, and intervening period in mosquito twelve days or more). In the remaining 20 inoculations the interval in the mosquito was less than twelve days, which circumstance alone would explain the negative result. It really surprises me that anybody can take this table as an argument in favour of the three days’ infectiousness. The responsibility for this dogma rests with Marchoux and Simond, and theirs should be the honour for having enunciated it, should it finally prove to be correct, but proved it they have not. I have, in a former paper, analyzed the four experiments which sustain their argument, and shall not go irto details here. All four experiments are with infection of blood or filtered serum, and in only one was the infected individual proved, by subsequent mosquito inoculation, susceptible to yellow fever. The experiments are, therefore, both very few and of very relative value. Never has a dogma in medicine been established on evidence poorer than this. Taking the facts as they are known at present, then, it appears that a mosquito may become infected at a port—Guayaquil, for example—and that mosquito will not become dangerous until twelve days have elapsed.