V. Evaluation of Cross-Immunity against Type 1 Dengue Fever in Human Subjects Convalescent from Subclinical Natural Japanese Encephalitis Virus Infection and Vaccinated with 17D Strain Yellow Fever Vaccine
Twelve attempts at man to man transmission by bites of Anopheles freeborni infected with Plasmodium cynomolgi, seven with the M strain and five with the B strain, were successful. These results suggest that normal, i. e. mosquito, transmission of these two strains from man to man can occur with a high degree of frequency.
Observations for the B strain infections were: (1) the prepatent periods ranged from 15 to 20 days (av. 17.6); (2) maximum parasitemia was 150 per cmm of blood; (3) the first day of recorded fever ranged from 15 to 20 days; (4) maximum temperature was 104°F; (5) only one infection began with a tertian fever pattern; and (6) gametocytes were demonstrable in three infections.
Observations for the M strain infections were: (1) the prepatent periods ranged from 16 to 37 days (av. 19.9); (2) maximum parasitemia was 300 per cmm of blood; (3) the first day of recorded fever ranged from 16 to 19 days; (4) maximum temperature was 104.6°F; (5) tertian fever patterns developed in four infections; and (6) gametocytes were demonstrable in three infections.
The predominant symptoms for all infections were cephalgia, anorexia, nausea, and myalgia. Splenomegaly was more frequent and extensive in the M strain infections. Clinical manifestations did not correlate with the degree of parasitemia. The disease syndrome is considered to be mild.
Sporozoite induced M strain infections appeared to be more “virulent” than sporozoite induced B strain infections.
Characteristics of infections induced by blood inoculation of the B strain (5 cases) and the M strain (6 cases) are described.
A. freeborni can become infected when fed on human beings with low P. cynomolgi gametocyte levels. Relatively few bites of these mosquitoes can produce simian malaria infections in man.