THE TOLL OF THE MOSQUITO 9 



of transmission is well understood. It is now definitely estab- 

 lished that the disease is conveyed in nature only through the 

 bite of an infected female Aedes calopu s mosquito. 



It is believed that the mosquito becomes infected by biting 

 persons suffering from yellow fever during the first 3 days of 

 the fever, experiments indicating that the infective principle 

 disappears from the blood after that period. The mosquito, 

 however, is unable to transmit the disease until about 12 days 

 after it has sucked the blood; from then on, it remains infected 

 all its life and may communicate the disease to several persons 

 successively. 



So far as is known, man is the only animal subject to yellow 

 fever, attempts to infect other animals having failed. 



The fact that the mosquito can be infected only during the first 

 3 days of the disease is an important factor in prevention of 

 yellow fever, since if the patient can be isolated from mosquitoes 

 during this period, no mosquitoes will be infected and, hence, 

 the disease cannot spread. Difficulty in diagnosing yellow fever 

 sometimes renders this impossible. 



Although yellow fever has been a scourge for centuries, it was 

 not until 1900 that the role of the mosquito in transmitting this 

 dread plague was ascertained and the preventive measures, 

 based thereon, developed. This epoch-making discovery was 

 made by a board of American army medical officers. Previously, 

 it had been believed that the infection was carried in clothing, by 

 the air, etc. 



MORTALITY AND MORBIDITY 



Although yellow fever in the United States today is virtually 

 eliminated, the terrible epidemics of former years in which panic 

 reigned throughout the South are not yet forgotten. In South 

 and Central America, the disease is still epidemic in many places, 

 as well as in other parts of the world. But modern medical and 

 engineering science is routing it all along the line. 



The following compilation from the U. S. Public Health Service 1 

 reports of cases occurring in various North, South and Central 

 American countries during the fiscal years indicated, is admit- 

 tedly incomplete and should be considered only as an indication 

 of the areas in which the disease is more or less endemic : 



1 Annual Reports, U. S. Public Health Service, 1918, 1919, 1920 and 1921. 





