Retinal changes in uncomplicated and severe Plasmodium knowlesi malaria

Plasmodium knowlesi causes severe malaria, however its pathogenesis is poorly understood. Retinal changes provide insights into falciparum malaria pathogenesis, but have not been studied in knowlesi malaria. An observational study was conducted in Malaysian adults hospitalized with severe (n=20) and non-severe (n=24) knowlesi malaria using indirect ophthalmoscopy (n=44) and fundus photography (n=29). Median age was 44 (range 18-74) years. No coma or deaths occurred. Photography detected retinal changes in 11/12 (92%) patients with severe and 14/17 (82%) patients with non-severe knowlesi malaria. Non-specific retinal whitening occurred in 3 (35%) and 5 (29%) patients with severe and non-severe disease, respectively; haemorrhages in 2 (17%) and 3 (18%); loss of retinal pigment epithelium in 1 (8%) and 4 (24%); and drusen in 9 (71%) and 12 (75%). All changes were mild, with no differences between severe and non-severe disease. Patients with retinal haemorrhages had lower platelets than those without (median 22 vs 43x10(9)/L, p=0.039). The paucity of specific retinal findings associated with disease severity in knowlesi malaria contrasts with the retinopathy of severe adult falciparum malaria with and without coma, suggesting that falciparum-like microvascular sequestration in the brain is not a major component in severe knowlesi malaria pathogenesis.