circular to elliptical in shape and measure 20 micrometres in diameter at day 6 and 40–60 micrometres at day 14. The cytoplasm stains pale blue. The nucleus is about 1 micrometre in diameter. There are no morphological features to distinguish them from any other Plasmodium species. The life cycle in the mosquito has been studied in several species. Although the details differ somewhat between species the outline is broadly similar. The oocysts have a maximum diameter between 30 and 100 micrometres (mean 60 micrometres). Sporozoites appear in the salivary glands about day 14. Transmission to human volunteers has not been successful. Vectors Anopheles (Nyssorhynchus) albimanus Anopheles (Anopheles) argyropus Anopheles (Anopheles) atroparvus Anopheles (Cellia) balabacensis balabacensis Anopheles (Cellia) balabacensis introlatus Anopheles (Cellia) dirus Anopheles (Anopheles) donaldi Anopheles (Anopheles) freeborni Anopheles (Cellia) hackeri Anopheles (Cellia) kochi Anopheles (Anopheles) letifer Anopheles (Cellia) maculatus Anopheles (Anopheles) peditaeniatus Anopheles (Cellia) philippinensis Anopheles (Anopheles) quadrimaculatus Anopheles (Anopheles) sinensis Anopheles (Cellia) stephensi Anopheles (Cellia) vagus Hosts P. fieldi infects the kra monkey (Macaca irus or Macaca fascicularis ), the rhesus monkey (Macaca mulatta), the pig-tailed macaque (Macaca nemestrina), the bonnet macaque (Macaca radiata) and the baboon (Papio doguera). References fieldi Parasites of primates