Malaria and splenomegaly in the Punjab.

Splenomegaly and parasitaemia were correlated in 2891 children examined in outpatient clinics during 13 consecutive months in 4 Punjabi villages. The average monthly splenomegaly rate varied from 0.05-0.13 before the monsoon malaria transmission season to 0.18-0.27 during and after this season. Moderate splenic enlargement reached a peak during the malaria transmission season, while the highest proportion of very enlarged spleens occurred towards the end of, and after, the transmission season. Children with splenomegaly were 3 times more likely to have Plasmodium falciparum and 1.5 times more likely to have P. vivax parasitaemias than were children without palpable spleens. The larger the spleen the more likely a P. falciparum infection, whereas P. vivax was more commonly associated with minimal spleen enlargement. Although the probability of a child with splenomegaly having a malaria parasitaemia was highest (0.58-0.72) during and immediately following periods of malaria transmission, the odds ratio of malaria infections among those with splenomegaly to those without was at its lowest (1.41-2.11) during those months. Mean P. falciparum parasitaemias were significantly higher in infected children with moderately enlarged spleens than in infected children with nonpalpable spleens or in those with minimal or extensive splenomegaly. These results are compatible with splenomegaly being a result of both the malaria infection and the immune response. Early in infection many children had parasitaemia without splenomegaly; after the parasitaemia had cleared splenomegaly often persisted.