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There should be a recognisable trend between the incidence of hypereosinophilia and the duration of tropical endomyocardial fibrosis (EMF), if the hypothesis, that EMF is the burnt out phase of eosinophil associated heart disease, is correct. We tested this hypothesis in a prospective study of 89 consecutive EMF cases over an 18 year period at two Nigerian locations (Ife in South West and Calabar in South East). We carefully dated the duration of EMF symptoms at first presentation and screened for hypereosinophilia (eosinophilia > or = 1500/mm3), and their causes. When no cause was identified for hypereosinophilia we gave a therapeutic trial with diethylcarbamazine to the patients. An eosinophil count > or = 1000/mm3 was recorded in 80% of 24 cases seen within 6 months; 55% of 46 cases seen 0-24 months; 54% of 18 cases seen 25-48 months and 21% of 25 cases seen more than 49 months of onset of symptoms: while the respective distribution of eosinophil count > or = 1500/mm3 for similar periods were 66, 44, 27 and 21%. This reflects a highly significant (P < 0.001) inverse relationship between hypereosinophilia and the duration of EMF and strengthens the concept that EMF (without eosinophilia) represents the late stage of eosinophilic heart disease. The localisation of endemic EMF to the low-lying tropical rain forest Zone and its predominant occurrence among rural dwellers and farmers suggest a vector borne etiologic agent. Microfilaria was the most likely cause of hypereosinophilia in the cases presented.

Over a two-year period, 44 patients had an eosinophil count above the 97th centile. Thirteen of these 44 had heart disease presenting within six months of the onset of symptoms. Microfilariasis was the most likely cause of the raised total eosinophil in these 13 patients. In all, the raised eosinophil count we returned to normal by the use of diethylcarbamazine (Banocide). Eleven of the 13 were followed up and eight of them (73%) developed clinical features of cardiac constriction and tricuspid regurgitation. The mean duration of follow-up was two years. Limited cardiac catheterisation studies in six of the patients showed evidence of constriction or of tricuspid regurgitation. The clinical features of these eight patients were indistinguishable from those found in chronic endomyocardial fibrosis. This disease was further suggested by recurrent cerebral embolism in one, and a large pericardial effusion in another; and it was also present in the one patient to come to necropsy. Thus, microfilaria-induced eosinophilia, when high, is frequently associated with heart disease which appears to be chronic endomyocardial fibrosis many months after the eosinophilia has returned to normal.