Muellerius capillaris in north-east Zaire: prevalence in sheep and goats and determination of intermediate hosts

Muellerius capillaris was the only species of nematode recovered from the lungs of young and adult sheep and goats of north-east Zaire. The prevalences were of 19% (sheep) and 32% (goats). The slug Atoxon pallens contained larvae in natural conditions and represents a potential intermediate host. The land snails Achatinidae (Achatina stuhlmanni and Limicolaria spp.) could not be experimentally infected with M. capillaris larvae.     

Experimental Oesophagostomum bifurcum in monkeys

OESOPHAGOSTOMUM BIFURCUM: larvae, cultured from human stools collected in northern Ghana, were used to establish experimental infections in monkeys. A patent infection was established in a rhesus monkey (Macaca mulatta) and this infection was used to generate larvae to inoculate additional monkeys. In all, 17 animals were inoculated. Thirteen of 15 animals developed antibodies to the infection between 19 and 62 days post inoculation (PI); two animals had a positive response before inoculation. Four of ten animals developed patent infections between 88 and 134 days and passed eggs in the faeces. Egg shedding was consistent in only one animal, but at low levels of one or two eggs per 2 mg direct smear, and extended over a 400 day period. In the other three animals, egg shedding was sporadic and of only 2-4 weeks duration. In seven animals necropsied between 19 and 22 days PI, one to 17 early fourth-stage larvae were recovered from nodules in the bowel wall; in an eighth animal examined at 314 days, six immature adult worms (early fifth stage) were recovered from nodules in the bowel wall. The morphological features and growth of these recovered larvae are described. Three animals were inoculated with larvae that had been dried for one week at 28 degrees C; two animals began shedding eggs at 128 and 134 days PI, respectively. The present results suggest that the parasite obtained from humans is poorly adapted to lower primate hosts, and supports the concept that Oesophagostomum bifurcum found in humans and monkeys in the same geographical region of northern Ghana and Togo are distinct and that the infections in humans are not likely to represent zoonotic infections acquired from monkeys.     

Blowflies Calliphora vicina and Lucilia sericata as passive vectors of Mycobacterium avium subsp. avium, M. a. paratuberculosis and M. a. hominissuis

Mycobacterium avium subsp. paratuberculosis (Actinomycetales: Mycobacteriaceae) isolates of identical restriction fragment length polymorphism (RFLP) type B-C1 were isolated from: intestinal mucosa of two cows showing clinical signs of paratuberculosis, a specimen of the blowfly Calliphora vicina Robineau-Desvoidy (Diptera: Calliphoridae) captured while perched on these cattle intestines in a waste container at the site of the slaughter, and the blowflies C. vicina and Lucilia caesar Linnaeus captured the next day at the same site when no infected cattle with paratuberculosis were slaughtered. Subsequently, second-stage larvae of the blowflies C. vicina and Lucilia sericata (Meigen) were experimentally infected by feeding them liver from hens with avian tuberculosis caused by M. a. avium (serotype 1, genotype IS901+ and IS1245+) and small cuts of pork meat contaminated with M. a. hominissuis (serotype 8, genotype IS901- and IS1245+). Mycobacterium a. avium of identical serotype, genotype and RFLP type F-C3 was isolated from C. vicina larvae on days 4 and 11 post infection (p.i.) and from L. sericata larvae on day 4 p.i. Identical RFLP type B-C1 of M. a. paratuberculosis was isolated from adult C. vicina fed with artificially contaminated saccharose solution on day 2 p. i. Investigation of M. a. paratuberculosis distribution inside the adult C. vicina showed that the majority of Colony Forming Units (CFU) were isolated from the abdomen and head, fewer from the thorax and wings and none from the legs. Larvae and adults may participate in spreading causal agents of mycobacterial infections and this fact should be considered during sanitation of infected herds and in slaughterhouses when materials from animals affected by mycobacterial infections are processed.     

Morphology of inhibited larvae of the bovine lungworm Dictyocaulus viviparus.

Some morphological features of inhibited fourth stage (L4) and fourth moult larvae (4M) of the bovine lungworm Dictyocaulus viviparus are described. Inhibition was induced by maintaining the third stage larvae (L3) for 6 weeks at 4 degrees C. Inhibited fourth stage (L4) and fourth moult larvae (4M) were collected by perfusion of the lungs of experimentally infected calves after necropsy at 15 and 68 days post infection (d.p.i.), respectively. Inhibited 4M, isolated at 68 d.p.i., were about ten times larger than inhibited L4 isolated at 15 d.p.i.     

Survival of sheep and goat first stage protostrongylid larvae in experimental conditions: influence of humidity and temperature

The survival of first-stage larvae of a laboratory strain of Muellerius capillaris and of a natural multispecific infection (Neostrongylus linearis, Cystocaulus nigrescens, Protostrongylus rufescens) was studied for 10 to 12 day periods. The survival was estimated either on larvae in faeces or kept in tap water. Temperature (-18 degrees C to 37 degrees C) and desiccation were the ecological factors investigated. M. capillaris was the most tolerant to these factors but showed better survival at 4 degrees C (and at -18 degrees C on one occasion). N. linearis survived better at 25 degrees C or -18 degrees C and C. nigrescens at 4 degrees C and -18 degrees C. Humidification of faeces was unfavourable to the latter species. All the species could stand desiccation of faeces up to 67% of dry-matter for M. capillaris or 82% for other species. Larval survival estimated for L1 in tap water was different from that estimated for larvae in faeces. The variation in resistance to unfavourable temperatures or moisture conditions may account partly for the geographical distribution of the species.     

Experimental concurrent infection of Afar breed goats with Oestrus ovis (L1) and Haemonchus contortus (L3): interaction between parasite populations, changes in parasitological and basic haematological parameters

The study was conducted to examine the occurrence and interaction between Oestrus ovis and Haemonchus contortus in experimentally infected Ethiopian Afar breed of goats. Twenty goats were divided into four groups (O, OH, H, and C) of five animals each. Each animal of groups O and OH received weekly infections for 5 weeks with 66 first instar larvae (L₁) of O. ovis. Then animals of groups OH and H were infected with a single dose of 5000 third stage larvae (L₃) of H. contortus. Goats of group C were kept free of any infection as non-infected control. Faecal egg count (FEC), blood cell count, total serum protein level and body weight were recorded weekly throughout the study period. At necropsy worm burden, female worm length, fecundity and larval burden of O. ovis in the nasal-sinus cavities of infected animals were assessed. The results showed that the presence of H. contortus in the abomasum of goats of group OH had no influence on the development of O. ovis. On the contrary, a significant reduction (P < 0.05) in FEC, worm burden, fecundity and female worm length was revealed in group OH animals compared to the mono-infected animals (group H). This was associated with eosinophilia and reduced packed cell volume.     

Resistance to ivermectin by Haemonchus contortus in goats and calves.

Efficacy of ivermectin on susceptible or resistant populations of the parasitic nematode Haemonchus contortus was determined in cattle and goats held in a barn. Goats were each infected with 3000 infective, ivermectin-susceptible or -resistant H. contortus larvae on day 0 and reinfected with 2000 infective larvae on day 24. Goats were treated orally with 600 micrograms kg-1 ivermectin on day 31. No significant differences were detected in blood packed cell volume (PCV) or total protein (TP), prepatent period, or epg among the four groups of goats that were each infected with one of four parasite strains (one susceptible, three resistant). There were no differences among the four parasite strains in the numbers of infective larvae that developed to the third larval stage from fecal cultures or in the viability of cultured infective larvae when held in the laboratory at 27 +/- 1 degrees C for 14 weeks. After treatment with ivermectin, there were significant differences among the parasite strains in PCV, TP, and epg. Total worm counts were reduced by 94 to 97% with three times the recommended dose. Immature and adult Skrjabinema ovis were also present in two treated goats. In a second test, one goat infected once with 10,000 infective larvae of a resistant strain of H. contortus and then treated with nine doses of ivermectin, increasing from 500 to 2000 micrograms kg-1 over a period of 133 days, had 35 adult worms at necropsy. In a third test, three calves were readily infected with an ivermectin-resistant strain of H. contortus from goats.(ABSTRACT TRUNCATED AT 250 WORDS)     

Eosinophilia in murine ancylostomiasis.

Eosinophil changes in the peripheral blood of singly and repeated infected mice were studied during murine ancylostomiasis. In singly infected animals, eosinophils began to rise on 1st day, reached a peak on 4th day and progressively declined from 9th to 30th day. In repeatedly infected animals, peak eosinophilia was observed during 3rd week of post infection and sustained upto 30th day with a slight decrease. These studies demonstrate that eosinophilia is induced due to antigen-antibody reactions in the host system and eosinophilia in helminthic infections is amnestic response.     

Innate immune response to Rift Valley fever virus in goats

Rift Valley fever (RVF), a re-emerging mosquito-borne disease of ruminants and man, was endemic in Africa but spread to Saudi Arabia and Yemen, meaning it could spread even further. Little is known about innate and cell-mediated immunity to RVF virus (RVFV) in ruminants, which is knowledge required for adequate vaccine trials. We therefore studied these aspects in experimentally infected goats. We also compared RVFV grown in an insect cell-line and that grown in a mammalian cell-line for differences in the course of infection. Goats developed viremia one day post infection (DPI), which lasted three to four days and some goats had transient fever coinciding with peak viremia. Up to 4% of peripheral blood mononuclear cells (PBMCs) were positive for RVFV. Monocytes and dendritic cells in PBMCs declined possibly from being directly infected with virus as suggested by in vitro exposure. Infected goats produced serum IFN-γ, IL-12 and other proinflammatory cytokines but not IFN-α. Despite the lack of IFN-α, innate immunity via the IL-12 to IFN-γ circuit possibly contributed to early protection against RVFV since neutralising antibodies were detected after viremia had cleared. The course of infection with insect cell-derived RVFV (IN-RVFV) appeared to be different from mammalian cell-derived RVFV (MAM-RVFV), with the former attaining peak viremia faster, inducing fever and profoundly affecting specific immune cell subpopulations. This indicated possible differences in infections of ruminants acquired from mosquito bites relative to those due to contact with infectious material from other animals. These differences need to be considered when testing RVF vaccines in laboratory settings.     

The Intestinal Expulsion of the Roundworm Ascaris suum Is Associated with Eosinophils,Intra-Epithelial T Cells and Decreased Intestinal Transit Time

Ascaris lumbricoides remains the most common endoparasite in humans, yet there is still very little information available about the immunological principles of protection, especially those directed against larval stages. Due to the natural host-parasite relationship, pigs infected with A. suum make an excellent model to study the mechanisms of protection against this nematode. In pigs, a self-cure reaction eliminates most larvae from the small intestine between 14 and 21 days post infection. In this study, we investigated the mucosal immune response leading to the expulsion of A. suum and the contribution of the hepato-tracheal migration. Self-cure was independent of previous passage through the liver or lungs, as infection with lung stage larvae did not impair self-cure. When animals were infected with 14-day-old intestinal larvae, the larvae were being driven distally in the small intestine around 7 days post infection but by 18 days post infection they re-inhabited the proximal part of the small intestine, indicating that more developed larvae can counter the expulsion mechanism. Self-cure was consistently associated with eosinophilia and intra-epithelial T cells in the jejunum. Furthermore, we identified increased gut movement as a possible mechanism of self-cure as the small intestinal transit time was markedly decreased at the time of expulsion of the worms. Taken together, these results shed new light on the mechanisms of self-cure that occur during A. suum infections.     

Effect of entomopoxvirus infection of Pseudaletia separata larvae on the oviposition behavior of Cotesia kariyai

Parasitoid behavior and oviposition were monitored to investigate the ability of Cotesia kariyai (Watanabe) (Hymenoptera: Braconidae) to distinguish between entomopoxvirus-infected and noninfected larvae of Pseudaletia separata Walker (Lepidoptera: Noctuidae). Comparison of individual means revealed that searching time was not significantly different between treatments. Ovipositional time, however, differed significantly after day 8 post virus inoculation. The parasitoid adopted ovipositional posture on infected and noninfected host irrespective of the stage of infection and did not distinguish infected from noninfected larvae up to 4 days post infection. Mean number of larvae stung by the parasitoid was not influenced by the length of time interval between exposure to the virus. However, duration of ovipositor insertion was influenced by the time interval between exposure to the virus and subsequent exposure to parasitoid females. Female parasitoids did not completely reject infected larvae as unsuitable for egg deposition. However, 5 days after virus inoculation they rejected significantly more infected than noninfected larvae. Furthermore, significantly more eggs were laid in noninfected than infected larvae from day 5 following virus administration. These observations suggest that probing by Cotesia kariyai may provide information concerning host suitability.     

Brugia pahangi in the BALB/C mouse: a model for testing filaricidal compounds

The BALB/C mouse infected with Brugia pahangi has been evaluated as a model for the selection of filaricidal compounds with activity against immature worms. Mice were infected by the intraperitoneal inoculation of 50 infective larvae and candidate compounds were administered by the intraperitoneal (i.p.), subcutaneous or oral route once daily from day 4 to day 8 post infection. Animals were examined on days 29 to 32 post infection. Variation in the larval recoveries from undrugged mice within and between experimental groups limited the value of drug assessments based upon percentage worm recoveries. The infection rate of undrugged mice was 85% over-all, range 60 to 100%. Using the infection rate of drugged v. undrugged animals as the criterion of activity the test has been evaluated with a series of standard nematicidal compounds. Levamisole and the benzimidazole carbamates, mebendazole, flubendazole and fenbendazole given i.p. at 10 mg/kg daily were active in this screen whilst DEC, DEC-N-oxide, ivermectin, amoscanate, metrifonate and suramin were inactive at the dosages tested. No retardation of growth or morphological abnormalities were observed in worms from the drugged mice.     

Litomosoides carinii: retardation of worm growth and of migration of challenge infections in jirds (Meriones unguiculatus)

Inbred jirds (Meriones unguiculatus) were divided into three groups; each animal in two of the groups was infected with 30 infective larvae (L3) of Litomosoides carinii. When these infections were patent, the jirds of one of the two infected groups plus those of the third group were injected with 30 L3 L. carinii each. All animals were killed either on day 14 or 24 after the second infection for the recovery, enumeration and measurement of all worms and developing larvae. Challenge larvae were stunted (smaller) and fewer than control larvae. Additionally, fewer challenge larva were recovered on day 14 than on day 24, indicating that migration to the pleural cavity was retarded.     

MCP-1 and MIP-2 levels during Echinococcus granulosus infections in mice

Ten BALB/c mice were infected with the cestode Echinococcus granulosus. After the infection, serum was collected at different periods of time and monocyte chemotactic protein-1 (MCP-1) and macrophage inflammatory protein-2 (MIP-2) were determined. The level of MCP-1 increased from at day 20 post infection (p.i.), to a maximum of on day 60 p.i., then decreased to on day 130 p.i. A second peak was observed at day 150 p.i. In addition, MIP-2 was detectable in serum as late as day 100 p.i. The highest level was observed on day 130 p.i., and decreased thereafter. Serum from noninfected animals (controls) contained no detectable levels of either MCP-1 or MIP-2. However, MCP-1 and MIP-2 appear to be implicated in E. granulosus infections, but their exact role during the disease is under determination.     

Strongyloides ratti: Susceptibility to infection and resistance to reinfection in inbred strains of mice as assessed by excretion of larvae

Eleven inbred strains of mice, and one outbred strain, were infected with Strongyloides ratti and larvae in the faeces were quantitated. Three strains, C57B1/6, CBA and BALB/c mice were susceptible to infection while other strains demonstrated negligible infections as assessed by this method. Larvae were first seen in the faeces on day 5, peak levels were reached on days 6 and 7, and excretion ceased 10 days after infection. Factors influencing intensity of larval excretion were examined in C57B1/6 mice. Young mice (1 month of age) were found to be more susceptible to infection than 2 and 6 month old animals. Male mice were much more susceptible to infection than female animals. There was a direct relationship between the number of S. ratti injected and the number of larvae excreted over the range 200–1600 larvae; subsequent increments in dose of injected larvae failed to increase the larval output. Infection by the percutaneous route resulted in a heavier infection than did subcutaneous injection. Previous exposure to S. ratti induced a profound resistance to reinfection. It is suggested that S. ratti infections of C57B1/6 and CBA mice provide a useful model for the investigation of factors influencing the host-parasite relationship in strongyloidiasis.     

Whole-body analysis of a viral infection: vascular endothelium is a primary target of infectious hematopoietic necrosis virus in zebrafish larvae

The progression of viral infections is notoriously difficult to follow in whole organisms. The small, transparent zebrafish larva constitutes a valuable system to study how pathogens spread. We describe here the course of infection of zebrafish early larvae with a heat-adapted variant of the Infectious Hematopoietic Necrosis Virus (IHNV), a rhabdovirus that represents an important threat to the salmonid culture industry. When incubated at 24 °C, a permissive temperature for virus replication, larvae infected by intravenous injection died within three to four days. Macroscopic signs of infection followed a highly predictable course, with a slowdown then arrest of blood flow despite continuing heartbeat, followed by a loss of reactivity to touch and ultimately by death. Using whole-mount in situ hybridization, patterns of infection were imaged in whole larvae. The first infected cells were detectable as early as 6 hours post infection, and a steady increase in infected cell number and staining intensity occurred with time. Venous endothelium appeared as a primary target of infection, as could be confirmed in fli1:GFP transgenic larvae by live imaging and immunohistochemistry. Disruption of the first vessels took place before arrest of blood circulation, and hemorrhages could be observed in various places. Our data suggest that infection spread from the damaged vessels to underlying tissue. By shifting infected fish to a temperature of 28 °C that is non-permissive for viral propagation, it was possible to establish when virus-generated damage became irreversible. This stage was reached many hours before any detectable induction of the host response. Zebrafish larvae infected with IHNV constitute a vertebrate model of an hemorrhagic viral disease. This tractable system will allow the in vivo dissection of host-virus interactions at the whole organism scale, a feature unrivalled by other vertebrate models.     

Kinetics of primary and secondary infections with Strongyloides ratti in mice

Dawkins H. J. S. and Grove D. I. 1981 Kinetics of primary and secondary infections with Strongyloides ratti in mice. International journal for Parasitology11: 89–96. The kinetics of infection with S. ratti were quantitated in normal and previously exposed C57B1 /6 mice. In primary infections, larvae penetrated the skin rapidly and were seen in peak numbers 12 h after infection. By 24 h after infection, larval numbers had declined appreciably and there was a slow decrease in numbers thereafter. Larvae were first observed in the lungs at 24 h and maximal recovery occurred at 48 h. It is thought that larval migration through the lungs is rapid. Worms were first seen in the intestines two days after infection. Maximum numbers were seen on the fifth day and worm expulsion was complete by day 10. Two moults took place in the small intestine during days 3 and 4 after infection. Rhabditiform larvae were first noted on the fourth day after infection. Mice exposed to S. ratti four weeks previously had significantly less larvae in the skin 4 and 12 h after infection but by 24 h there was no difference when compared with mice with primary infections. Peak recovery of larvae from the lungs occurred 24 h after infection; significantly less larvae were recovered on days 2 and 3 when compared with normal mice. There was a marked reduction in the adult worm burden in the gut; the number of worms recovered was less than one fifth of that seen in primary infections. Those worms which did mature were less fecund and were expelled from the intestines within 7 days of infection. It is suggested that in previously exposed animals, the migration of larvae from the skin is hastened, many of these larvae are destroyed in the lungs and that expulsion of worms which do mature in the intestines is accelerated.     

Response to ivermectin treatment of parasitic stages of Haemonchus contortus resistant or susceptible to ivermectin.

Two groups of 33 helminth-naive lambs were infected with 5,000 L3 of an ivermectin-resistant or -susceptible strain of Haemonchus contortus (groups R and S). On days 6, 10, 16, and 21 postinfection, 5 animals from each group were chosen at random and orally treated with 0.2 mg/kg of ivermectin. On each occasion, 2 randomly selected lambs from each group were also killed to determine the number and stage of development of the worms present at the time of treatment. These necropsies revealed that by day 6 early and late fourth-stage larvae were present, whereas on day 10 the early fifth stage had been reached; by days 16 and 21 all worms had reached the adult stage. Necropsies on day 28 postinfection revealed that although animals treated at day 6 had 26.3% fewer worms than the controls, there was no significant difference (P greater than 0.05) between worm burdens from any of the animals infected with the R strain and treated at different times after infection when compared with the untreated controls. With ivermectin significant reductions were obtained in the worm burdens of the animals infected with the susceptible strain; these were reduced by 96% when treatment was given on day 6 against fourth-stage larvae and 98.9% when the drug was given on day 21 against adult stages. From these results it is clear that resistance to ivermectin in this strain of H. contortus is present as early as the fourth larval stage.     

Apoptosis as a post-phagocytic winnowing mechanism in a coral–dinoflagellate mutualism

This study was aimed at detecting apoptosis as a post-phagocytic mechanism of symbiont selection during the onset of symbiosis in larvae of the scleractinian coral Fungia scutaria. Larvae were infected with one of three Symbiodinium types: freshly isolated homologous ITS-type C1f from adult F. scutaria , heterologous C31 from adult Montipora capitata , known to be unable to successfully colonize F. scutaria larvae, and type B1 from the symbiotic sea anemone Aiptasia spp. Apoptosis was detected by the activation of caspases, enzymes specific to apoptosis. Caspase activity was measured in situ by cleavage of a specific fluorophore and detection with confocal microscopy. At 6 h post infection, there was a significant increase in caspase activation in gastrodermal cells in C31-infected larvae, compared with larvae infected with C1f or B1 types. Compared with control larvae infected with C31, which had decreased infection rates present by 24 h post infection, when C31-infected larvae were incubated with a broad-scale caspase inhibitor, the per cent of larvae infected with C31 did not significantly decrease over time. This indicates that the reduction in infection success observed in untreated C31-infected larvae can be rescued with inhibition of caspases and apoptosis. This suggests the presence of a post-phagocytic recognition mechanism. Larvae infected with freshly isolated B1 retained infection success over time compared with C31-infected larvae, suggesting that there is host discrimination between heterologous algae. Initiation of this post-phagocytic response may occur more readily with a highly specific heterologous symbiont type such as C31, compared with a generalist heterologous type such as clade B1.     

Muellerius capillaris (Mueller, 1889) (Nematoda: Protostrongylidae): an unusual finding in Rocky Mountain bighorn sheep (Ovis canadensis canadensis Shaw) in South Dakota

Lungs and fecal samples from nine hunter-killed Rocky Mountain bighorn sheep were examined for lungworms. All samples contained adults and/or larvae of Muellerius capillaris (Mueller, 1889). Protostrongylus spp., the lungworms commonly reported from bighorn sheep, were not present in any samples. Larvae of M. capillaris bear a spine on the dorsal side of the posterior end and are shorter than dorsal-spined larvae of other lungworms recorded from North American ungulates. Larvae similar in shape but longer than those of Muellerius were found in free-ranging bighorn sheep in Alberta and British Columbia. In addition, dorsal-spined larvae have been found in bighorn sheep in Montana, North Dakota, and Washington. The identity of the dorsal-spined larvae is known only from sheep in South Dakota. Thus, caution must be taken when diagnosing lungworm infections in Rocky Mountain bighorn sheep.