The susceptibility to praziquantel of Schistosoma haematobium in the baboon (Papio anubis) and of S. japonicum in the vervet monkey (Cercopithecus aethiops)

Research paper by C. James, G. Webbe, G. S. Nelson

Indexed on: 01 Jan '77Published on: 01 Jan '77Published in: Zeitschrift fur Parasitenkunde (Berlin, Germany)


Baboons infected with S. haematobium and vervet monkeys infected with S. japonicum were treated orally with different dosage regimens of praziquantel. The progress of the infections in the primates was followed by weekly faecal and urine egg counts before and after treatment. The response to treatment was also monitored by observing oogram changes in rectal snips. The baboons and vervet monkeys were autopsied and perfused 3–4 months after treatment.The results of the praziquantel treatments of baboons infected with S. haematobium show that a single administration of 100 mg/kg in one day was as effective as 50 mg/kg for five consecutive days in producing a complete cure. A single dose of 30 mg/kg failed to stop egg laying but retreatment with 50 mg/kg administered in one day resulted in cessation of egg laying 12 days after treatment and only one immature female worm and 33 male worms were recovered at autopsy. A baboon treated with 30 mg/kg administered at 10 mg/kg three times in one day was not cured, but when retreated with 75 mg/kg, administered in three separate doses of 25 mg/kg in one day, egg laying stopped 15 days afterwards and only three male worms were recovered at autopsy. The results suggest that a single oral dose of 75–100 mg/kg bwt is likely to be effective against S. haematobium in the baboon. An intramuscular injection of 200 mg/kg bwt was well tolerated by one animal.The results obtained with praziquantel against S. japonicum in the vervet monkey show that a complete cure was obtained in the animal given 50 mg/kg on five consecutive days, but the regimens of a single dose of 20 mg/kg followed by two separate doses of 10 mg/kg during one day, and of 10 mg/kg given three times during one day, resulted in only partial parasitological cures.The results based upon faecal egg output studies and the oograms taken after treatment suggested that praziquantel is more effective against S. japonicum than S. haematobium in the doses given, but the subsequent autopsies showed that some S. japonicum adult worms had survived treatment.A baboon naturally infected with S. mansoni, with a daily egg output of 150 eggs, was completely cured by a single oral dose of 50 mg/kg of praziquantel. This dose however failed to cure another naturally infected animal with a daily egg output of 1,800 eggs.It is considered that a predominant characteristic in the pathology of the animals given a curative dose of praziquantel was the total resolution of cellular reaction and fibrosis in the tissues containing known numbers of dead residual eggs. In the baboons with S. haematobium, the ureters and bladder had recovered their functional integrity and in the vervet monkeys infected with S. japonicum, a similar resolution of pathology in the liver and bowel was apparent.The results show that praziquantel is effective against patent S. haematobium and S. mansoni infections in baboons and against S. japonicum in vervet monkeys, in relatively low dosage regimens (100 mg/kg and < 100 mg/kg) applied in one day, as shown by suppression of egg laying and reduction or complete elimination of adult worms. Female worms of S. haematobium are apparently more susceptible to the compound than male worms. The classic hepatic shift of adult schistosomes was observed in all of the primates treated in the present series, but histopathological studies showed that numerous worms also died in situ, while only a few were found in the lungs.