Studies on the experimental transmission of Capillaria philippinensis in monkeys

Abstract

Embryonated eggs of Capillaria philippinensis fed to 3 species of freshwater fish from northern Luzon, Philippine Islands hatch in the digestive tract and the larvae increase in size becoming infective within 3 weeks. 34 monkeys were fed experimentally infected fish, digestive tracts from fish, or larvae recovered from the digestive tracts of fish, and 21 became infected. One monkey died 30 days after receiving 30 larvae and 926 worms were recovered at autopsy. Eggs were found in the faeces of 20 monkeys and the prepatent periods ranged from 22–96 days and averaged 46 days. The egg laying periods were also variable and ranged from 10 days to over one year. Daily egg counts were computer analysed and pooled data from 8 monkeys suggested that peak egg outputs occurred at 22 ± 6 days. Some monkeys died while others were killed and in most animals significantly more Capillaria philippinensis were recovered than originally introduced. All stages of the nematode were found including oviparous and larviparous females, adult males and various developmental stages of the parasite. These findings are consistent with those previously reported from humans and confirms that autoinfection is part of the life cycle of Capillaria philippinensis. None of the infected monkeys became ill or manifested symptoms of infection although several of the animals demonstrated patent infections for more than a year. The reasons for this are not known, nor can an explanation be offered for infections not developing in all monkeys that were exposed to larvae from experimentally infected fish. The 3 species of fish found to serve as experimental intermediate host were Eleotris melanosoma, Ambassis commersoni and Apogon sp. Eleotris melanosoma is always eaten cooked, Ambassis commersoni is always eaten raw and Apogon sp. is eaten either raw or cooked. Two specimens of Apogon sp. were found naturally infected with a capillarid larva. These species of fish should be considered as potential sources of the parasite in the capillariasis endemic areas of the Philippines.