Recovery of Schistosoma japonicum from Experimentally Infected Pigs by Perfusion of Liver and Mesenteric Veins

Abstract

An optimized procedure for perfusion of pigs infected with Schistosoma japonicum was developed. The technique involves insertion of a perfusion influx tube into the thoracic descending aorta, clamping vessels to parts of the body which did not need to be perfused (the kidneys, hind legs, etc.) and placing a collection tube directly into the portal vein. In addition, the clamping technique allows for separate perfusion of the liver and intestinal veins. The perfusion medium was a sodium citrate buffer (40°C) to which the vasodilator sodium nitroprusside was added. Furthermore, an experiment was conducted to investigate if the perfusion efficiency, measured by total worm recovery, could be increased if praziquantel was administered prior to perfusion. Twelve pigs were each infected with 1 000 S. japonicum cercariae and their schistosomes were collected 11 weeks later by separate perfusion of the liver and intestinal veins. Six of these pigs were treated orally with praziquantel one hour before perfusion. In general, the vessels of the livers and intestines of all pigs were well perfused, judging by the resulting pale colour of the tissues. Worms from praziquantel treated pigs were collected within 5 min of perfusion as opposed to approximately 20 min in the non-treated pigs. More worms were collected from the livers of the praziquantel treated pigs, indicating a hepatic shift of schistosomes from the intestinal mesenteries. However, comparable numbers of worms were retained in the mesenteric veins following perfusion in the 2 groups, indicating that manual recovery of schistosomes from the intestinal mesenteries is necessary in addition to perfusion for obtaining the total worm counts. Another experiment was conducted to determine if the intensity and/or duration of infection had an effect on the number of worms collected by the perfusion technique. Seventy-two pigs were allocated into 3 groups of 24 pigs each, which were infected with either 100, 500 or 2 000 cercariae per pig. The 3 groups were further divided into 4 subgroups of 6 pigs each which were perfused with our selective technique at 4, 11, 17 or 24 weeks post infection, respectively. All of the pigs received an oral praziquantel treatment prior to perfusion. The results indicated that increasing intensities and/or duration of infection resulted in trapping of schistosomes in intravascular inflammatory reactions which made it more difficult to collect the adult schistosomes by perfusion.

Sammendrag

En optimeret procedure til perfusion af den kinesiskc blodikte, Schistosoma japonicum, ud af mesenterialvenerne hos grise beskrives. Metoden bygger på, at så meget som muligt af influx-væskens tryk kanaliseres igennem mesenterialvenerne. Derudover indgives et parasit-paralyserende ormemiddel (Praziquantel) oralt inden den egentlige perfusion. En plastik-slange indsættes i den decenderende aorta, blodkar til dele af kroppen, som ikke skal perfunderes, aflukkes med en pean, og en opsarnlingsslange indsættes dirckte i portal-venen. Y dermere tilsættes det kardilaterende stof, natriumnitroprussid, til perfusionsmediet, som er 40°C varmt. Effektiviteten af den optimerede metode blev testet i to forsøg. Perfusionstiden kunne reduceres betydeligt, idet ormene passivt blev skyllet til leveren efter ormebehandlingen. Derimod kunne en efterfølgende manuel under-søgelse af venerne omkring tarmen ikke undgås på trods af den optimerede procedure, idet der stadig fandtes enkelte såkaldte residualorm i de eksperimentelle grupper. Dette skyldtes i nogen grad, at en del af blodikterne sent i infektionsforløbet var lokaliseret i intravaskulære inflarnmatoriske reaktioner, som gjorde perfusion af dem umulig.