CONTROL OF MALARIA IN PANAMA WITH DRUGS 
279 
TABLE VIII 
Species of Malaria Parasites Found in 
2,939 Positives 
Species of 
parasites 
Chagres 
New San 
Juan 
Madden 
Highway* 
Rio Pescadot 
Totals 
P. falciparum . 
782 
744 
528 
54 
2,108 
P. vivax . 
163 
86 
135 
21 
405 
P. malariae . 
21 
10 
52 
4 
87 
P. falciparum & 
P. vivax . 
90 
80 
99 
4 
273 
P. falciparum & 
P. malariae . 
15 
10 
16 
1 
42 
P. vivax and P. 
malariae . 
2 
1 
11 
0 
14 
P. falciparum, vi¬ 
vax & malariae 
3 
2 
5 
0 
10 
Totals . 
1,076 
933 
846 
84 
2,939 
* Five years records of Chilibre and Madden 
Highway schools. Infrequent surveys. 
t One survey, August 1940, in a town on Gatun 
Lake. A period of ten years for New San Juan 
and the Chagres villages. Monthly surveys. 
5 Chagres River villages. Of course this 
figure was obtained from the results of 
single examinations; if a series of exami¬ 
nations had been made in the same indi¬ 
viduals, probably more would have been 
found. However, it is not an easy task to 
find in any one survey a suitable crescent- 
carrier for mosquito infection experiments. 
This is true of the untreated control areas, 
as well as of the treated groups. The 
TABLE IX 
Incidence of P. Falciparum Crescents in Five 
Chagres River Villages and in Madden 
Highway Control Groups 
Years 
Chagres 
Villages 
Madden 
Highway 
Rio 
Pescado 
1931-32 
13.2 
28.7 
1932-33 
29.2 
34.6 
1933-34 
22.8 
17.9 
1934-35 
28.2 
25.3 
1935-36 
26.5 
18.3 
1936-37 
39.8 
31.7 
1937-38 
44.0 
27.2 
1938-39 
37.9 
25.6 
1939-40 
45.1 
54.8 
38.9 
crescent rate is apparently higher in these 
treated groups, but this may be only the 
result of more frequent examinations. The 
gametocyte carrier is still a great problem 
in areas where drug control is attempted. 
Table X shows the interesting and im- 
TABLE X 
Annual Percentage of Heavy Malarial In¬ 
fections During the Past Ten Years 
Years 
Five Chagres 
River villages 
(treated) 
Madden High¬ 
way and Dam 
(controls) 
1930-31 
16.7 
6.5 
1931-32 
11.6 
8.8 
1932-33 
21.8 
19.6 
1933-34 
15.0 
12.2 
1934-35 
20.0 
17.4 
1935-36 
15.0 
11.3 
1936-37 
19.3 
10.5 
1937-38 
17.3 
10.0 
1938-39 
20.4 
12.9 
1939-40 
23.1 
10.3 
portant fact that a greater percentage of all 
malarial infections were “heavy” among 
the eases found in the treated Chagres 
River groups than in the untreated control 
groups. Heavy infections were more nu¬ 
merous in the treated groups after 10 years 
of treatment than they were in the early 
years of our work. Yet the average annual 
malarial parasite rate in the treated groups 
in 1939—40 was only 12.1 per cent, while in 
the initial survey made in 1929 the rate was 
46.5 per cent. 
We believe that a partial explanation of 
this otherwise discouraging fact lies in the 
possibility that treatment of all parasite¬ 
positive cases rids so many of them of 
parasites that immunity is lost. When 
such individuals with lowered immunity 
become newly infected, they are more 
likely to be clinically ill, with many para¬ 
sites in the blood, than are others who 
retain a few parasites at all times but 
rarely become actively ill. 
Of the 20 infants found positive in the 
control areas, the first infection of at least 
one was found in each month of age from 
