Changed conditions in the area under observation, and the desire to check further the conclusions reached in the last annual report of this work (5), induced us to continue observations under the same plan as last year.
Monthly blood-parasite surveys in three groups treated with atabrine-plasmochin, quinine-plasmochin, both under adequate supervision, and with quinine sulphate under no supervision, gave average monthly rates for the year of 9.1, 12.3, and 18.5 per cent, respectively. The higher rate in the quinine control group was probably due to lack of supervision, and a higher percentage of children in this group (see table 2). As in the past years, the rates showed no correlation with monthly rainfall. The 12 months covered by this report were a period of low incidence, following the epidemic period of 1935, thus corroborating the views set forth in our fifth report concerning the cyclic nature of malaria incidence in Panama. The fact that our observations were made during a down-swing of the incidence curve must be considered in interpreting our results during the past year.
The parasite rate, cumulative for the 12 months, but limited to those examined at every monthly survey, shows that slightly more than half of this group had parasites in the blood during the year (table 5). The same table shows that a rather high annual parasite rate can exist in all age-groups of a relatively tolerant people. The same phenomena in connection with relapse occurred during the past year as were noted in our previous reports, and we believe that relapse, especially during a year of low incidence, is responsible for a great part of the malaria rate observed.
The influence of adequate treatment in lowering the blood parasite rate during an interepidemic period is well shown in table 7.
Individual monthly records of all persons examined in 12 consective surveys, who were found positive two or more times, are given in tables 8, 9 and 10.
Table 11 shows the incidence of species of malaria parasite found in the 811 positives discovered during the year. Estivoautumnal (subtertian) infections predominate, as in the past, and tertian infections are slightly more common in the control group. Few crescent-carriers were discovered in the surveys during the year. Heavy infections were somewhat more numerous in the two treated groups than in the control.
Sixty-six infants were examined at some time during their first year of life, some only once, some for a number of months. The combined rate was 9.1 per cent, which is comparatively low, and indicates a season of low transmission. During the previous year, in which an epidemic occurred, 28 infants examined an average of 5 times, gave an annual rate of 25.0 per cent.
We believe that infected adults, even though relatively tolerant to malaria infection, will not be able to support the strain of daily hard labor without the aid of medical attention. We believe this can be most economically given by supplying non-medical personnel in the field, to given immediate antimalarial treatment to those who become clinically ill; such non-medical personnel should be supervised by a qualified physician interested in tropical and industrial medicine, who should make weekly visits of inspection.
Our previous experience has shown the impossibility of eradicating malaria by reducing the “seed-bed” of infection in young children and adolescents by the use of drugs. However, we do not doubt that control of malaria to a point where it will interfere little with the supply of native labor is economically possible under our local conditions by the method outlined above.
Expenditures for such measures of control are economically justifiable, as they doubtless will result in increased labor efficiency, commensurable with the financial outlay involved.
Director, Gorgas Memorial Laboratory, Panama, R. de P.
Sanitary Engineer, United States Public Health Service.