Peter Nansen

Heterologous antagonistic and synergistic interactions between helminths and between helminths and protozoans in concurrent experimental infection of mammalian hosts.

Experimental concurrent infection with two or more parasite species in mammalian host models may result in heterologous antagonistic and synergistic interactions ranging in magnitude from reduced/enhanced growth and fecundity to blockage/enhancement of establishment/expulsion. With some exceptions only, there is a reasonable correlation between the levels of interaction monitored by parasitological and by clinico-pathological parameters. Heterologous antagonistic interactions mediated by functional and specific immunological cross-reactivity occur between closely related parasite species exhibiting a marked immunobiological similarity. In contrast, antagonistic interactions between antigenetically more remote species of helminths, protozoan-induced resistance to helminth infection and helminth-induced suppression of concurrent protozoan infection generally appear mediated by immunologically non-specific factors like macrophage activation and inflammatory reactions. Synergistic heterologous interactions between helminths, helminth-induced enhancement of concurrent protozoan infection and interference with the development and maintenance of resistance to helminth infection in response to concurrent protozoan infection are generally thought to be mediated by non-specific parasite-induced immunosuppression. Concurrent experimental infection is very complex. There are problems and limitations in extrapolating from experimental studies on concurrent infection in laboratory animals to natural polyparasitism. This fact, coupled with the complex influence of ecological factors on the pattern and frequency of concurrent natural infection means that major consequences of natural concurrent parasite infection have not been definitively demonstrated. Appropriately planned and controlled field studies and further laboratory experiments on primate and domestic animal models are imperative for elucidation of the importance of heterologous interactions in concurrent parasite infection for the disease pattern in man and domestic stock. Experimental studies hitherto conducted on concurrent parasite infection pointing to natural heterologous interactions may be a valuable starting point for further studies.

In vitro stress selection of nematophagous fungi for biocontrol of parasitic nematodes in ruminants.

Laboratory experiments were designed to select nematophagous fungi that were able to survive in vitro conditions simulating passage through the gastro-intestinal tract of cattle. All of the tests were conducted at 39 degrees C. In a primary stress selection step in diluted rumen fluid, 21 isolates were obtained. Each of the primary stress selected isolates was tested in synthetic saliva, rumen fluid simulating the activity in the rumen, rumen fluid followed by pepsin-hydrochloric acid treatment simulating the additional effect of ruminal and abomasal activity, pepsin-hydrochloric acid solution simulating conditions in the abomasum and finally in a trypsin solution as an example of enzyme activity in the gut. The effect of the rumen fluid alone, or rumen fluid followed by pepsin-hydrochloric acid treatment, were responsible for the reduction in surviving fungal isolates. Only six of thirteen isolates belonging to the genus Arthrobotrys survived while seven of eight isolates of the genus Duddingtonia survived. Fourteen isolates were tested for their predatory capacity in a dung pat bioassay. Fungi of the genera Arthrobotrys and Duddingtonia reduced the development of Ostertagia ostertagi third stage larvae by approximately 75% and 96% respectively compared to the number of larvae that developed from fungus-free control pats.

Effect of papaya latex against Ascaris suum in naturally infected pigs

An experiment was carried out to investigate the anthelmintic activity of papaya latex (Carica papaya) against natural infection of Ascaris suum in pigs. Sixteen naturally infected pigs were, on the basis of faecal egg counts and body weight, allocated into four groups, each of four pigs. Three groups (groups B, C, and D) were given papaya latex per os at dose levels of 2, 4, and 8 g of papaya latex per kg body weight, respectively. The fourth group (group A) served as a non-treated control. Results of post mortem counts on day 7 post treatment revealed worm count reductions of 39.5, 80.1 and 100% in groups B, C, and D, respectively. Some of the pigs receiving the highest dose of the latex showed mild diarrhoea on the day following treatment. Otherwise, no clinical or pathological changes were observed in the treated animals. The possible future use of this traditional herbal medicine for livestock and humans is discussed.

Parasites in cross-bred pigs in the Upper East region of Ghana.

A cross-sectional study was carried out in the Upper East Region (UER) of Ghana in order to estimate the prevalence of parasitic infections in local cross-bred pigs. Out of 60 villages with a human population of 200-1000 inhabitants, 10 villages were randomly selected for the study. The number of pigs varied from 50 to 200 pigs per village. In total 259 faecal samples from growers were collected and examined. Ninety-one percent of the animals excreted parasite eggs. Among these the prevalence of Eimeria spp. was 77.2%, Isospora suis (27%) and Balantidium coli (19.3%).The following helminth eggs were identified: Metastrongylus salmi (19.3%); Physocephalus sexalatus (17.4%); Oesophagostomum spp./Hyostrongylus rubidus (60.6%); Trichuris suis (4.6%); Ascaris suum (12.7%); Ascarops strongylina (8.1%); Brachylaemus suis (1.9%); Paragonimus suis (0.8%); Globocephalus urosubulatus (2.7%); and Schistosoma suis (0.4%). Furthermore, six growers were selected from each village for clinical and postmortem examinations, i.e. 60 in total. The clinical examinations revealed ectoparasites on 98.3% of the animals. The ectoparasites were: Haematopinus suis (66.7%); Boophilus spp. (58.3%); Amblyomma spp (45.0%); Sarcoptes suis (38.3%); and Rhipicephalus spp. (8.3%). All pigs were examined for the presence of haemoparasites. It was found that 23.3% of the animals had haemoparasites. These were: Babesia perroncitoi (23.3%); Babesia trautmanni (13.3%); and Eperytrozoon suis (1.7%). Based on postmortem examinations the following adult worms were identified: Metastrongylus salmi (83.3%); Oesophagostomum dentatum (63.3%); Oesophagostomum quadrispinulatum (38.3%); Hyostrongylus rubidus (23.3%); Ascarops strongylina (76.7%); Globocephalus urosubulatus (20.0%); Strongyloides spp. (1.7%); and Physocephalus sexalatus (65.0%). Cysts of the human tapeworm Taenia solium, Cysticercus cellulosae, were present in 11.7% of the animals. Small pieces of the diaphragm were examined for the presence of Sarcocystis spp.. The prevalence was 28.3%, but no larvae of Trichinella spp. were found. Furthermore, four of the animals (6.7%) had Taenia hydatigena cysts.

A cross-sectional study of helminths in rural scavenging poultry in Tanzania in relation to season and climate.

A cross-sectional study on the prevalence of helminths in rural scavenging poultry on six hundred adult chickens selected randomly from six villages in the Morogoro Region, Tanzania during the wet and the dry seasons, was conducted. The trachea and gastrointestinal tract of each bird were examined for the presence of parasites. All chickens were infected with one or several species of helminths, the average being 4.8 +/- 1.7 helminths per chicken during the wet season and 5.1 +/- 1.8 during the dry season. A total of 29 different helminth species were shown in the trachea or the gastrointestinal tract. The following species were identified: Syngamus trachea (0.7% (wet season), 2% (dry season)); Gongylonema ingluvicola (6.3%, 17.7%); Tetrameres americana (54.3%, 60.3%); Dispharynx nasuta (0%, 2.7%); Acuaria hamulosa (8.3%, 19.3%); Ascaridia galli (28.3%, 32.3%); Heterakis gallinarum (74.0%, 78.7%); H. isolonche (18.7%, 5.0%); H. dispar (25.7%, 6.3%); Allodapa suctoria (40.0%, 52.0%); Subulura strongylina (3.3%, 1.0%); Strongyloides avium (0.3%, 3.0%); Capillaria annulata (2.0%, 0.0%); C. contorta (9.0%, 1.0%); C. caudinflata (2.0%, 4.3%); C. obsignata (8.7%, 25.0%); C. anatis (4.0%, 9.0%); C. bursata (1.0%, 2.7%); Raillietina echinobothrida (41.3%, 46.3%); R. tetragona (25.3%, 21. 3%); R. cesticillus (8.7%, 2.7%); Choanotaenia infundibulum (0.0%, 3. 7%); Hymenolepis carioca (9.0%, 18.0%); H. cantaniana (48.0%, 43. 0%); Amoebotaenia cuneata (39.3%, 36.0%); Metroliasthes lucida (1.0%, 0.3%); Davainea proglottina (5.7%, 0.3%) and Polymorphus boschadis (0.3%, 0.0%). No trematodes were found. No correlation was found between season and prevalence, or season and mean worm burdens. Twelve helminths of the species recovered represent new local records.

Biological control of trichostrongyles in calves by the fungus Duddingtonia flagrans fed to animals under natural grazing conditions

The present study was conducted in the 1993 grazing season with yearling calves exposed to a pasture with a natural mixed trichostrongyle larval infection. It was shown that daily feeding with the microfungus Duddingtonia flagrans during the first 2 months of the season led to a lowered herbage infectivity and a reduced acquisition of Ostertagia sp. and Cooperia sp. later in the season. In addition, the procedure delayed the onset of clinical disease. This was due to the nematode-destroying effects of the fungi in the dung excreted by the fungus-treated calves, as evidenced by results from a parallel in vitro assay on faecal larval cultures. The paper discusses future research needs before practical biological control can be implemented.

Biological control of nematode parasites in cattle with nematode-trapping fungi: a survey of Danish studies

In Denmark two series of experiments have been performed to study the interactions between larvae of bovine gastrointestinal nematode parasites and nematode-trapping fungi. For practical reasons we were interested in the possibility of depositing nematode-trapping fungi in cattle faeces after passage through the gastrointestinal tract. In the first series, laboratory tests with the fungus Arthrobotrys oligospora showed that motile free-living larvae of a wide range of animal-parasitic nematodes and some soil-living nematodes effectively induce the formation of traps. Larvae of all parasitic nematodes are rapidly captured in these traps. The induction of nets was influenced by temperature, number of larvae, atmosphere, light, and media composition. Captured first- and second-stage larvae were quickly penetrated and killed while third stage larvae were killed slowly, perhaps because they are partially protected by an outer dead sheath. Laboratory and field studies showed that when A. oligospora material was directly mixed into dung a significant reduction in the number of infective parasite larvae in the dung and surrounding herbage occurs. This reduction was also reflected in the acquired worm burden of calves grazing on fungal treated pasture. However, the A. oligospora strain studied in the above mentioned experiments did not survive passage through the alimentary tract of cattle. This prompted us to start a second series of experiments to isolate fungi that could survive gut passage of cattle. Different soil and compost samples were screened by an in vitro stress selection technique. This simulated certain important stress factors which occur during passage through the alimentary tract of ruminants. Rumen exposure was found to be a major limiting factor, but some Arthrobotrys and Duddingtonia strains survived submersion in rumen fluid. In a subsequent in vivo experiment, some of these survivors were fed to calves, and it was hereby demonstrated that isolates of both genera, i.e. Arthrobotrys and Duddingtonia, were able to survive passage through calves and significantly reduce the number of developing preparasitic larvae in dung of fungal treated calves. In a controlled field experiment, isolates of Duddingtonia reduced the level of infective third-stage larvae in herbage by 74-85%.

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.

In vivo passage through calves of nematophagous fungi selected for biocontrol of parasitic nematodes

The experiment was designed to test the survival and performance of stress selected nematophagous fungi after passage through the gastro-intestinal tract of cattle. Ruminating calves were fed daily with a fixed amount of fungal material grown on barley grains. The excreted dung was collected on days four and five after the start of the feeding experiment. Barley grains were washed out of the excreted dung and incoculated on water-agar plates. After incubation for one week, nine of ten fungal isolates were re-isolated from these plates. The predatory capacity of the fungi in the excreted faeces was tested in a dung pat bioassay and a faecal culture system. In the dung pat bioassay, two fungi of the genus Arthrobotrys and six of the genus Duddingtonia reduced the development of Ostertagia ostertagi third stage larvae by 85% (61%-93%), compared to the number of larvae developed from fungus-free control pats. In seven out of these eight isolates, the reduction of larvae in the faecal cultures was 92% (76%-99%).

Biological control aspects of biological control—with special reference to arthropods, protozoans and helminths of domesticated animals

Biological control describes situations in which a living antagonist (a predator, parasite, parasitoid or a pathogen) is distributed by man to lower pest (parasite) populations to acceptable sub-clinical densities or to keep the population at a non-harmful level. Ideally, biological control has no negative effects on the environment, whereas chemical control is not always so harmless. Laboratory and field observations have revealed many organisms, such as viruses, bacteria, fungi, protozoans, turbellarians, nematodes, earthworms, tardigrades, insects, copepods and mites as antagonists to parasitic arthropods, protozoans and helminths of domesticated animals. However, only very few of these antagonists have shown promising qualities as biological control agents within veterinary science. The lack of success should be linked to the lack of knowledge about complex natural biological systems and the antagonists that may be found there. This situation has restricted the interest of industry in developing biological products. In the future, however, industry may become more interested in biological control considering the increasing problems with parasite resistance to drugs in combination with the increasing cost of developing new chemical products, and because of increasing public concern about chemical residues in animal products and in the environment.