Spleen and Parasite Rates as Measures of Malaria in the Caribbean Area

Abstract
Summary 1. The parasite rate, employing the thick blood film method, on 11,000 adult Haitian negroes was 23.5 per cent, while the same test on 1102 of their children showed a rate of 41.9 per cent. 2. The spleen rate on these same adults was 3.05 per cent and on the same children was 22.78 per cent. 3. Of the 2585 adult negroes whose blood films were positive for the parasites of malaria, only 110 had palpable spleens. Therefore, 2475 men with malaria would have been overlooked had the spleen index alone been employed. Of the 462 children whose blood films were positive for malaria, 175 had palpable spleens. Therefore, 287 children with malaria would not have been considered infected if we had used only the spleen index. 4. Of the 335 adult negroes who had palpable spleens, 225 did not have malarial parasites in their blood films. Of the 251 negro children who had palpable spleens, 76 failed to reveal parasites in their blood films. Two hundred and sixty-four, or 78.7 per cent, of the palpable spleens found in the adult negroes were barely palpable; while 131, or 52.2 per cent, of the palpable spleens in the children were of the same type. It is possible that all the palpable spleens recorded, even though not associated with parasites in the blood films, represented latent or recent malaria. Nevertheless, the error in the spleen rate was so much greater than in the parasite rate that it has great significance for those of us who wish to treat the active cases of malaria in an adult male labor force, or even in the general inhabitants of a community. The thick blood film examination of a large labor force or community on a single day does not, of course, disclose all of the individuals who may be positive for malaria. Interval surveys are indicated. The combined application of the blood and the spleen surveys would have greater value in the Latin-American labor forces, because the spleens of this race seem to show a greater degree and more permanent reaction to malarial infections than the spleens of the West Indian negroes show. I think, however, that the thick blood film survey, even in the Latin Americans, will include nearly all of the malarial infections that are active. 5. The application of both the parasite and spleen survey methods will fail to detect all cases of malarial infections, as can be easily proved by the routine examination at autopsy of films prepared from the rib marrow and splenic pulp. 6. Of the 335 palpable spleens found in these adult negroes, only 71, or 21.2 per cent, were below the costal margin. Of the 251 palpable spleens found in the negro children, 120 or 47.8 per cent were below the costal margin. The spleens which extended below the costal margin were not associated, in any regular manner, with the group of individuals showing “heavy parasite” infections in their blood films. These large spleens were very likely due to malarial chronicity rather than to one or two acute attacks. 7. Extreme cases of splenic enlargement, 1000 grams or more in weight, were commonly found in the Latin American labor class of the autopsy series; and were very rarely encountered in the negro, even though he had lived for a number of years on the mainland under the same environment as the Latin Americans. 8. Analysis of the autopsy series of cases indicates that acute enlargement of the spleen in negroes is more significant and constant in typhoid fever and lobar pneumonia than in malaria of the estivo-autumnal type. 9. The approximate range in weight of the normal spleen in these negroes is, apparently, 140 to 160 grams. See tables 7, 11 and 16. 10. It would appear, from analysis of the clinical records associated with the weights of the spleen at autopsy, that in adults this organ must exceed 300 grams in size before palpation can score a very high rate of success. See table 9. 11. The series of lobar pneumonia cases in the negro (table 8) revealed spleens with a weight in excess of 300 grams in 20 cases; yet in 6 instances, or 30 per cent, these spleens were not palpable. A disease of this nature may interfere with a low excursion of the diaphragm, which would ordinarily force the spleen down; and an inflated stomach and intestine could further handicap efforts in palpation. 12. These series of cases, in the autopsy records on cases dying from some of the various causes of external violence, indicate that the approximate normal weight of the spleen in the West Indian negro is 130 to 150 grams; while in two groups of 7 and 8 cases of the Latin Americans, it was for Panama and Honduras respectively 325 and 456 grams. A group of twelve white people from the United States gave an average weight of 122 grams. Two adult Chinese men revealed an average weight of 80 grams. The body weight and height do not have as much relation to the size of the spleen as one might think. Race seems to play a more important rôle than the size of the body. See tables 7, 11, 12, 13 and 16. It is not considered safe to assume that the average spleen weight given here for the Latin American labor class is their normal spleen weight, even though the cases recorded were persons who were apparently in good health prior to the time that they lost their lives due to some form of external violence. It seems probable that there is a more permanent reaction of the spleen to former or latent diseases in this race than in the other races mentioned. It may be true that the descendants of the African race do not respond to the malarial stimulus to the same degree that the natives of Central America do. Perhaps, this feature tends to show that malaria was imported to the Caribbean area during the days of slavery.

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