Counter-regulatory anti-parasite cytokine responses during concurrent Plasmodium yoelii and intestinal helminth infections in mice

Malaria and helminth infections are two of the most prevalent parasitic diseases globally. While concomitant infection is common, mechanisms contributing to altered disease outcomes during co-infection remain poorly defined. We have previously reported exacerbation of normally non-lethal Plasmodium yoelii malaria in BALB/c mice chronically infected with the intestinal trematode Echinostoma caproni. The goal of the present studies was to determine the effect of helminth infection on IFN-gamma and other key cytokines during malaria co-infection in the P. yoelii-E. caproni and P. yoelii-Heligmosomoides polygyrus model systems. Polyclonally stimulated spleen cells from both E. caproni- and H. polygyrus-infected mice produced significantly lower amounts of IFN-gamma during P. yoelii co-infection than malaria-only infected mice. Furthermore, the magnitude of IFN-gamma suppression was correlated with the relative amounts of IL-4 induced by these helminths (E. caproni=low; H. polygyrus=high), but not IL-10. Concurrent malaria infection also suppressed helminth-associated IL-4 responses, indicating that immunologic counter-regulation occurs during co-infection with malaria and intestinal helminths.

Exacerbation of Plasmodium yoelii malaria in Echinostoma caproni infected mice and abatement through anthelmintic treatment

The effect of chronic intestinal trematode infection on malaria was examined in a murine model of co-infection using Echinostoma caproni and Plasmodium yoelii. BALB/c mice (n = 32) infected with a low dose of E. caproni (approximately 10 cysts) 25-35 days before malaria infection displayed significantly increased malaria parasitemia (P = 0.01), extended patency of malaria (P = 0.03), and increased fatality (47%; P < 0.001) compared to mice infected only with P. yoelii (17X nonlethal strain) (n = 18). Further analysis revealed that differences in malaria parasitemia between fatal co-infections and infections with P. yoelii only were highly significant (P < 0.0001), whereas nonfatal co-infections were not statistically different. Exacerbation of malaria was demonstrated to be reversible through clearance of E. caproni worms by praziquantel treatment administered 10 days before malaria infection. No deaths were observed during malaria infection in mice cleared of their E. caproni infection (n = 10), and parasitemia was significantly reduced from that of untreated co-infected mice (P = 0.03) and was not different from that of mice infected with P. yoelii only. Further studies examining parasite-parasite interactions and host immune response in the echinostome model are warranted to understand the mechanisms affecting the course and outcome of malaria infection during concomitant helminth infection.

Effects of a diet deficient in the B complex vitamins on infectivity, growth and distribution of Echinostoma caproni in ICR mice

The effects of a diet deficient in the B vitamins on infectivity, growth, and distribution of Echinostoma caproni in ICR mice were studied. The vitamin-deficient diet (experimental) was isocaloric to the control diet but lacked the B vitamins. Thirty-six female, 6- to 8-week-old ICR mice were each infected with 25 metacercarial cysts. From the day of infection to the day of necropsy, 18 mice were fed the experimental diet and the remaining mice received the control diet. Equal numbers of experimental and control mice were necropsied at 2, 3 and 4 weeks postinfection (p.i.). Mice on the experimental diet showed a significant loss in body weight between 2 and 4 weeks p.i. There was no significant difference in worm recovery at 2 to 4 weeks p.i. from mice on either diet. Worms from hosts on the experimental diet were more dispersed and located more posteriad in the small intestine than those from mice on the control diet. Worm dry weight was significantly less in hosts on the experimental diet at all weeks p.i. compared with that of hosts on the control diet. The body area of worms on the experimental diet was significantly less at 2 and 3 weeks p.i. than that of worms on the control diet. An isocaloric diet deficient in the B vitamins had a detrimental effect on the growth of E. caproni in ICR mice.

Antibody responses against Echinococcus multilocularis antigens in naturally infected Rattus norvegicus

Two Norway rats, Rattus norvegicus, were found to be naturally infected with Echinococcus multilocularis in Japan. One of them was simultaneously infected with at least three different sized metacestodes of Taenia taeniaeformis. These two R. norvegicus rats and another R. norvegicus naturally infected with T. taeniaeformis and Capillaria hepatica were examined to see if they showed any antibody responses against these two cestode parasites with the view to obtaining more information on the importance of rats as the intermediate host for E. multilocularis. These R. norvegicus showed very poor antibody responses against the two cestode species, although the Wistar rats, R. rattus, experimentally infected with a single smaller sized metacestode of T. taeniaeformis showed stronger responses not only against T. taeniaeformis but also against E. multilocularis. Therefore the three R. norvegicus naturally infected with E. multilocularis and/or T. taeniaeformis demonstrated virtually no immune response, at least against these cestodes.

A comparison of the adult and miracidial stages of Echinostoma paraensei and E. caproni

Adult Echinostoma paraensei and Echinostoma caproni were grown in outbred mice and golden hamsters to compare size, growth rates, infectivity, and habitat selection. Antagonistic responses between the 2 species were investigated by concurrent infections in mice. Miracidial stages were compared for developmental stages, hatching responses, and behaviour to light and gravity. Size differences and growth rates were significantly different in both mice and hamsters. Mice proved to be better hosts for E. caproni and hamsters for E. paraensei. In mature infections, E. paraensei adults localized in the duodenum and E. caproni in the ileum of both mice and hamsters. In concurrent infections of mice, E. paraensei adults were significantly smaller than in single species infections beyond 14 days post-infection, while E. caproni adults were either equal to or larger than those in single species infections. On the other hand, E. paraensei were recovered in larger numbers in concurrent infections than in single species infections, while the reverse was found for infectivity of E. caproni adults. Miracidia of E. paraensei developed at the same rate as those of E. caproni in both light and dark cultures, but E. paraensei hatched much sooner when exposed to light. No miracidia hatched from cultures kept in the dark, indicating light is needed to stimulate the hatching process. All light-stimulated cultures exhibited a circadian hatching pattern from 1100 to 1600 hours. Cultures maintained in the dark past 11 days did not hatch when exposed to light. Miracidia of E. paraensei showed a positive phototaxis but no response to gravity. This comparison of life cycle stages leads us to conclude that E. paraensei and E. caproni are distinct species.

A case of echinostomiasis with ulcerative lesions in the duodenum

Echinostomiasis is an endemic intestinal trematodiasis of humans in Korea. We observed a human case of Echinostoma hortense infection who had ulcerations on the duodenal mucosa. A 55-year old man living in Hamyang-gun, Kyongnam, complained of epigastric pain with hematemesis in April 1994. Endoscopy revealed lesions of early gastric cancer and duodenal ulcerations. A penetrating parasite into the duodenal mucosa was picked out, and identified as E. hortense. As the patient was treated with praziquantel 10 mg/kg single dose, 3 more E. hortense and 7 Metagonimus worms were recovered. This case demonstrates that echinostomiasis causes gross ulcerations in the duodenum.

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.

Concurrent infections of the trematode Echinostoma caproni and the tapeworms Hymenolepis diminuta and Hymenolepis microstoma in mice

Superimposing the intestinal tapeworm Hymenolepis diminuta on an established infection with the trematode Echinostoma caproni or simultaneous infection of mice with H. diminuta and Hymenolepis microstoma caused destrobilation and expulsion of H. diminuta, whereas establishment and growth of H. microstoma under the same infection regimes were not affected. In contrast, simultaneous superimposition of H. diminuta and H. microstoma on an established E. caproni infection caused destrobilation and expulsion of both H. diminuta and H. microstoma.

Single and concurrent infections of the golden hamster, Mesocricetus auratus, with Echinostoma revolutum and E. liei (Trematoda: Digenea)

Single or concurrent infections of the intestinal trematodes Echinostoma revolutum and E. liei were studied in the golden hamster (Mesocricetus auratus). In single infections, some hamsters were fed 25 +/- 5 metacercarial cysts and others 100 +/- 25 cysts of either E. revolutum or E. liei. In concurrent infections, hamsters were fed simultaneously 20 +/- 5 metacercarial cysts of E. revolutum and 20 +/- 5 cysts of E. liei or 100 +/- 25 cysts each of both trematodes. All hamsters exposed singly to E. revolutum or E. liei were infected. In concurrent infections, 9 of 10 hamsters were infected with both species of echinostomes, and the ratio of E. revolutum to E. liei was 3:1. In single infections, 80% of the E. liei and 60% of the E. revolutum were in the posterior third of the small intestine. In concurrent infections, 80% of the E. liei were in the posterior third and 57% of the E. revolutum in the middle third of the small intestine. The histopathological response of E. liei and E. revolutum in single and concurrent infections showed erosion of intestinal villi with lymphocytic infiltration as the primary response. Extraintestinal echinostomiasis occurred in 2 of the infection groups. Differences in hemoglobin and packed cell volume occurred in the different infection groups.

Heterologous synergistic interactions in concurrent experimental infection in the mouse with Schistosoma mansoni, Echinostoma revolutum, Plasmodium yoelii, Babesia microti, and Trypanosoma brucei

Primary infections with Plasmodium yoelii and Echinostoma revolutum in the mouse induced a significant increase in the heterologous Schistosoma mansoni challenge worm establishment, whereas S. mansoni worm establishment remained unaffected by primary infections with Trypanosoma brucei and Babesia microti. Concurrent infection in the mouse with P. yoelii or T. brucei, but not with B. microti, blocked the resistance to homologous E. revolutum challenge infection, and primary P. yoelii and T. brucei infections and corticosteroid treatment made naive, innately resistant mice susceptible to E. revolutum infection. Innate resistance to infection with E. revolutum, the pattern of expulsion of low-level E. revolutum infections, and resistance to homologous S. mansoni challenge infection remained unaffected by concurrent B. microti infection. Primary, heavy E. revolutum infections in the mouse resulted in the enhancement of subsequent infection with B. microti, whereas primary infection with S. mansoni suppressed subsequent B. microti infection in some but not all experiments. In a single experiment, P. yoelii infection was suppressed markedly by primary S. mansoni infection, whereas the enhancement of P. yoelii infection in concurrently E. revolutum-infected mice was seen in only one of the several experiments conducted. However, no interference with resistance to homologous B. microti and P. yoelii challenge infection was induced by concurrent infection with S. mansoni and E. revolutum. We suggest that the synergistic interactions demonstrated between protozoans and helminths in concurrent experimental infection in the mouse are induced by immunosuppression.

Impairment of primary expulsion of Echinostoma revolutum in mice concurrently infected with Schistosoma mansoni

The spontaneous expulsion of low-level Echinostoma revolutum infections was markedly impaired in mice harbouring 4-week-old Schistosoma mansoni infections at the time of infection with the echinostome.

Trypanosoma brucei-induced blockage of expulsion of Echinostoma revolutum and of homologous E. revolutum resistance in mice

Experiments were designed to study the effect of Trypanosoma brucei on the expulsion of Echinostoma revolutum and on the development and maintenance of homologous E. revolutum resistance in the mouse. T. brucei given 3, 2, and 1 wk before and 1 wk after infection with E. revolutum completely inhibited the expulsion of the E. revolutum worm burden for a period of at least 6 wk following infection, and T. brucei given 2 or 3 wk after infection with E. revolutum conferred a significant delay in the expulsion of the E. revolutum worm burden. T. brucei given 1 wk before and 1 wk after a primary E. revolutum infection blocked completely the resistance of the mouse to a homologous E. revolutum challenge given 2 wk after the primary infection. A similar blockage of resistance to a homologous challenge was experienced by mice given T. brucei 3 wk after the primary E. revolutum infection and challenged following another 2 wk. The mechanisms underlying the T. brucei-induced interference with the expulsion of E. revolutum and with the development and maintenance of homologous E. revolutum resistance in mice are presumably immunologically mediated.

Homologous immunotolerance and decreased resistance to Schistosoma mansoni in Echinostoma revolutum-infected mice

Homologous immunotolerance was demonstrated in Echinostoma revolutum infections in the mouse. High-level infections of about 15 worms were not expelled for a period of at least 61 days following infection, whereas low-level infections of about 10 to 12 worms or below were eliminated completely between day 47 and 61 after infection. A primary, 20- to 33-day-old, heavy E. revolutum infection in the mouse produced a statistically significant increase in the number of Schistosoma mansoni recovered in challenge infections. Worm burdens increased by 65.7 to 90.6% as compared with those of the respective S. mansoni challenge control groups.