Re-emergence of Plasmodium malariae in Trinidad, West Indies

A focus of Plasmodium malariae infection has recently occurred on the islan d of Trinidad, some 30 years after a successful eradication programme. Exam ination of bloodsmears revealed 22 cases of P. malariae in the Nariva-Mayar o area of Trinidad between August 1994 and September 1995. Most (77%) of th e cases were male and, as seven were aged <25 years of age, it appeared tha t transmission had been renewed, probably by the vector Anopheles bellator. However, none of the 3000 mosquitoes tested by ELISA for the circumsporozo ite protein of P. malariae proved positive. Use of IFAT to check blood samples for P. malariae appeared more sensitive than direct examination of bloodsmears, indicating that 42 (13%) of the 325 samples tested were seropositive (at titres of 1:256 or greater). The leve ls of transmission of the parasite may therefore be even higher than indica ted by examination of bloodsmears. The surveillance measures adopted to und erstand the epidemiology of this outbreak of P. malariae in Trinidad are de scribed. The need to maintain malaria surveillance in all the countries whe re P. malariae parasites once existed (prior to eradication) is emphasised.