A reassessment of the artificial infection of three predominant mosquito species with Plasmodium vivax in Shandong Province, China

Background & objectives: Under certain ecological circumstances, pathogens are able to rapidly adapt to new vectors. The great capacity of Plasmodium spp. to adapt to new anopheline mosquito vectors on different continents and the continuous ecological changes attributed to humans might promote their adaptation to culicine vectors, which are known to infect humans. Based on our current knowledge, it is difficult to predict whether such adaptations will occur. This study was aimed to determine the infection susceptibility of Anopheles sinensis, Culex tritaeniorhynchus and Cx. pipiens pallens to Plasmodium vivax in Shandong Province of China. Methods: The susceptibility of the three predominant species of mosquitoes -An. sinensis, Cx. tritaeniorhynchus and Cx. pipiens pallens in Shandong Province was compared with a direct membrane feeding assay with 15 batches of Shandong strain mono-infected gametocyte-containing blood collected from Plasmodium vivax-infected patients. Infectivity was measured by dissecting the midguts and salivary glands of the mosquitoes. The presence of oocysts and sporozoites was determined by microscopy at 6 and 22 days post-blood feeding. Results: From the 15 batches of mosquitoes that were fed infected blood, oocysts and sporozoites were detected only in 7th, 13th and 15th batches of infection for An. sinensis, and no oocysts or sporozoites were detected in Cx. tritaeniorhynchus or Cx. pipiens pallens. The positive rate of An. sinensis infection was 21.2, 13 and 36.3% in the three batches of mosquitoes, with an average infection rate of 23.5%. Interpretation & conclusion: The susceptibility of An. sinensis to P. vivax was very high in Shandong Province. Cx. tritaeniorhynchus and Cx. pipiens pallens failed to exhibit susceptibility to P. vivax.