The electronic fight against the schistosomes.

A DOS-compatible model for use on personal computers has been constructed for teaching in parasite epidemiology. The program is based on the Macdonald model of schistosome dynamics and enables simulation of the effect of a control campaign on a human worm load by reducing four transmission factors in the parasite life-cycle: (1) egg contamination, (2) snail lifetime, (3) exposure to cercariae and (4) adult worm lifetime.

Studies on the reproductive capacity of Echinostoma caproni (Trematoda) in hamsters and jirds.

Total egg output per infective stage inoculated was used as a measurement of the reproductive capacity in Echinostoma caproni infections in hamsters and jirds. Egg production per adult E. caproni recovered was comparable in the hamster and in the jird, but the reproductive capacity of E. caproni in infections with 6 metacercariae in the hamster markedly exceeded that in the jird. This was due mainly to the expulsion of worms from the jird. Eggs per gram faeces produced was shown to be an invalid parameter in comparing the reproductive capacity in E. caproni infections in jirds and hamsters due to differences in amounts of faeces produced, and evidence was obtained that uterine egg counts may not be a useful parameter in assessment of overall reproductive potentials. In the hamster, the reproductive capacity of infections with 25 or 6 metacercariae of E. caproni was comparable. This reflected a density independent recovery and egg production of the adult worms. The reproductive capacity, being an expression of the importance of a particular host species for the reproduction of a parasite population, is suggested as a convenient and useful quantitative parameter in the establishment of standardized criteria for evaluating host-parasite relationships in definitive host models.

Worm kinetics and serum IgE in hooded lister rats infected with the acanthocephalan Moniliformis moniliformis and the nematode Nippostrongylus brasiliensis.

After infection with the intestinal helminths Moniliformis moniliformis or Nippostrongylus brasiliensis, worm-specific IgE first appeared in the serum rats between days 10 and 24 p.i., varying with host age, worm species and worm dose used. The rate of increase in specific IgE was comparable regardless of the worm species, infection dose or host age and a peak response was observed about 1 month after the sera turned positive. In the M. moniliformis infections, these events took place long before the beginning of worm expulsion on day 63 in high-dose (50 worms) infections, and potentiation of heterologous IgE was not observed. In contrast, IgE stimulation by N. brasiliensis infections was detected as potentiation of anti-ovalbumin IgE, anti-M. moniliformis IgE and total IgE. Most of the total IgE in the serum of M. moniliformis-infected rats was likely to be the worm-specific IgE. Anthelminthic removal of M. moniliformis revealed that the presence of residual worms was necessary to maintain worm-specific IgE production.

The influence of stocking rate on transmission of helminth parasites in pigs on permanent pasture during two consecutive summers.

This study was made to elucidate the transmission of nematode infections in outdoor pigs at different stocking rates during two consecutive seasons. Five pigs (Group 1A) inoculated with low doses of Oesophagostomum dentatum, Ascaris suum, and Trichuris suis and five helminth-naïve pigs (Group 1B) were turned out together in June 1996 on each of four pastures at stocking rates of 100, 240 (two pastures) and 576m(2) per pig, respectively. The pigs were slaughtered in early October, and pasture infectivity was subsequently measured using helminth-naïve tracer pigs (Tracer). In 1997, 10 helminth-naïve pigs were turned out on each pasture in May (Group 2) and again in August (Group 3), and allowed to graze for 12 weeks. The percentage of grass cover was reduced considerably at the high stocking rate in comparison to the other stocking rates. Transmission of all three helminths was observed on all pastures. In 1996, the O. dentatum faecal egg counts and worm burdens were significantly higher in pigs at the high stocking rate compared to pigs at the other stocking rates. O. dentatum did not survive the winter and pigs of Group 2 were inoculated with 3000 larvae each to reintroduce this parasite. Ascaris suum ELISA values and worm counts were highest at the high stocking rate in 1997 (Group 3). Transmission of T. suis was not significantly influenced by stocking rate. The results indicate that transmission of O. dentatum, and to some extent A. suum is influenced by stocking rate. However, both A. suum and T. suis eggs are still expected to constitute a high risk of infection on intensively used pastures where eggs may accumulate for years. The relationship between host density and helminth transmission seems more complex for grazing/rooting pigs than for grazing ruminants. This may be due to the differences in behaviour of the animals and the resulting differences in microclimate of the developing eggs/larvae.

Prevalence and distribution of gastro-intestinal helminths and haemoparasites in young scavenging chickens in upper eastern region of Ghana, West Africa.

We conducted a cross-sectional study to determine the prevalence and species of gastro-intestinal helminths and haemoparasites in 100 chickens kept under extensive management systems in Ghana, West Africa. All the examined chickens (100%) were infected with gastro-intestinal helminths; a total of 18 species were detected. The species and their prevalences were: Acuaria hamulosa (25%), Allodapa suctoria (20%), Ascaridia galli (24%), Capillaria spp. (60%), Choanotaenia infundibulum (13%), Gongylonema ingluvicola (62%), Heterakis gallinarum (31%), H. isolonche (16%), Hymenolepis spp. (66%), Raillietina cesticillus (12%), R. echinobothrida (81%), R. tetragona (59%), Strongyloides avium (2%), Subulura strongylina (10%), Tetrameres fissispina (58%), Trichostronygylus tenuis (2%), and finally one unidentified acanthocephalan (1%) and one unidentified trematode (1%). Thirty-five per cent of the chickens were infected with the haemoparasites Aegyptinella pullorum and Plasmodium juxtanucleare (prevalences 9% and 27%, respectively). Association between chicken sex and prevalences was not significant. An over-dispersed distribution was seen for most of the helminth species.

Infectivity of Trichinella spp. recovered from decaying mouse and fox muscle tissue.

The tolerance to degradation processes in meat of nine Trichinella genotypes was studied in mouse and fox tissue, respectively. Minced muscle tissue with Trichinella larvae of different age was stored at room temperature at 100% relative humidity. During storage weekly sub samples of the minced meat were digested and released larvae were inoculated in mice to evaluate the Reproductive Capacity Index (RCI). The RCI decreased with the length of storage, but the larvae from older infections appeared better adapted to tolerate the degradation processes. The African species T. nelsoni had a relative higher tolerance to elevated temperature during storage and the unencysted species T. pseudospiralis was the most vulnerable genotype.

Nose-rings and transmission of helminth parasites in outdoor pigs.

Five growing pigs experimentally infected with low doses of Oesophagostomum dentatum, Ascaris suum, and Trichuris suis were turned out with 5 helminth-naïve pigs on each of 3 pastures in June 1996 (Group 1). On one pasture all pigs received nose-rings. After slaughter of Group 1 in October, pasture infectivity was monitored using helminth-naïve, unringed tracer pigs. In 1997, helminth-naïve young pigs were turned out on the contaminated pastures in May (Group 2) and again in August (Group 3). Again all pigs on one pasture received nose-rings. All pigs and pastures were followed parasitologically and reduction in grass cover was monitored. Based on the acquisition of infection by the naïve pigs in Group 1, the estimated minimal embryonation times for eggs deposited on pasture were 23-25 days for O. dentatum, 5-6 weeks for A. suum and 9-10 weeks for T. suis. Results from tracer pigs and grass/soil samples indicated that pasture infectivity was light both years. Free-living stages of O. dentatum did not survive the winter. The nose-rings reduced rooting considerably, resulting in three-fold more grass cover on the nose-ring pasture compared to the control pastures by the end of the experiment. Nevertheless, the nose-rings did not significantly influence parasite transmission.

Age-dependent occurrence of the intestinal ciliate Balantidium coli in pigs at a Danish research farm.

A cross sectional study of the prevalence and intensity of Balantidium coli in pigs was carried out on a Danish research farm. The prevalence of B. coli infection increased from 57% in suckling piglets to 100% in most pig groups > or = 4 weeks old. The mean number of cysts per gram faeces (CPG) of pigs aged 12 weeks and younger were < or = 206, whereas pigs aged 28 weeks and > 52 weeks had significantly higher counts of > or = 865 CPG. Although some lactating sows had very high CPG's, no significant differences in CPG could be detected between the intensities of pregnant sows, lactating sows and empty and dry sows. No human cases of B. coli infection have been published in Denmark though it is zoonotic.

The effect of temperature on the survival and infectivity of the free-living larvae of Nippostrongylus brasiliensis.

The development, survival and infectivity of larvae of Nippostrongylus brasiliensis at 10 and 21 degrees C have been studied. In cultures developed for 1 week at 21 degrees C but stored at either 10 or 21 degrees C the mean recovery of larvae in 1.5 h Baermann sediment (46% and 42% of total eggs, respectively) and their infectivity (66% and 70% day 8 p.i. recovery, respectively) at 4 weeks of cultivation were similar. However, at 20 weeks of cultivation only a few larvae survived storage at 21 degrees C (1.4%) and the survivors showed very low infectivity (4.1%), whereas larvae stored at 10 degrees C retained most of their survival and infectivity rates (41% and 44%, respectively). In cultures developed and stored at 10 degrees C a lower mean proportion (17%) of the eggs was recovered as larvae at 4 weeks of cultivation. The mean infectivity rate of these larvae increased from 4 to 12 weeks of cultivation (18% and 42%, respectively) but was reduced at 20 weeks of cultivation (27%). An increased proportion of adult female worms was recovered from rats infected with larvae from cultures showing poor development or survival and the fecundity of the adult females decreased in all groups as the storage time of the cultures was increased. Eggs from low fecundity adult worms showed normal development of larvae. The relation between survival, temperature in the habitat and the geographical distribution of the larvae of N. brasiliensis is discussed.

Immunological and histopathological reactions of the rat against the tapeworm Hymenolepis diminuta and the effects of anti-thymocyte serum.

Anti-thymocyte-serum (ATS) treated Wistar rats infected with 100 cysticercoids of the rat intestinal cestode Hymenolepis diminuta showed a delayed destrobilation and expulsion of the worms compared with saline-treated infected rats. This result strengthens previous evidence of an immunological nature of the destrobilation and expulsion in lumen-dwelling cestodes--even in their most susceptible hosts. The migration of the worms in the small intestine during the first 20 days of a primary 100-worm infection is described and the anterior migration of the destrobilated worms to the first 10% of the pylorus is emphasized and compared with similar migrations of the nematode Nippostrongylus brasiliensis in the rat. No serum antibodies were detected using passive cutaneous anaphylaxis and the indirect immunofluorescence test, although the thymus-independent areas of the mesenteric lymph nodes showed an increase in pyroninophilic cells. In the small intestine, no response to the tapeworm infection could be detected in pyroninophilic cells and globule leucocytes, but mast cell and eosinophilic cell numbers were increased in the saline-treated infected rats. Although the host responses to H. diminuta are shown to be thymus-dependent, the possibility of thymus-independent activity in the host reactions cannot be ruled out.

Effects of temperature and host density on the snail-finding capacity of cercariae of Echinostoma caproni (Digenea: Echinostomatidae).

The effect of temperature (19-36 degrees C) and snail host density (0.014-10 snails/l) on the snail-finding capacity of Echinostoma caproni cercariae is described. The initial swimming speed increased whereas the length of the infective period decreased with increasing temperature. The combined effect resulted in the E. caproni cercarial snail-finding capacity being temperature independent in the range 19 to 36 degrees C at a snail density of 0.014 snails/l. A moderate temperature dependency was, however, seen at a lower snail density. The cercarial snail-finding capacity was snail-host density dependent in the density range 0.014 to 1 snail/l. The findings from this study show that a relatively low and biologically realistic snail host density must be used in experimental studies if realistic estimates of the dynamics of cercarial transmission are to be obtained.

Echinostoma caproni in rats: worm population dynamics and host blood eosinophilia during primary infections with 6, 25 and 50 metacercariae and resistance to secondary and superimposed infections.

Hooded-Lister rats were inoculated with 6, 25, 50 or 100 metacercariae of the intestinal trematode Echinostoma caproni. Worm establishment and the pattern of egg excretion were followed during the course of primary infections with 6, 25 and 50 metacercariae. Peripheral blood eosinophilia was followed at all infection levels. After 1 month, worm recovery and faecal egg output showed a gradual decline with increasing duration of infection. High worm burdens were expelled later than smaller worm burdens, and egg output persisted longer in animals exhibiting a high initial egg output. The level of blood eosinophilia increased with increasing degree of infection and with the level of egg output. A marked concomitant resistance to superimposed infection was observed on the challenge of rats harbouring 21- and 49-day-old infections with 50 metacercariae. In addition, rats were partially resistant to secondary infection at challenge day 14 following anthelmintic removal of primary 7-day-old infections with 50 metacercariae and were completely resistant at challenge day 7 following elimination of a primary 14-day-old primary infection.