Jesper Monrad

Strongylus vulgaris associated with usage of selective therapy on Danish horse farms—Is it reemerging?

Nematodes belonging to the order Strongylida are ubiquitous in grazing horses, and the large strongyle Strongylus vulgaris is considered the most pathogenic. This parasite was originally described widely prevalent in equine establishments, but decades of frequent anthelmintic treatment appears to have reduced the prevalence dramatically. Increasing levels of anthelmintic resistance in cyathostomin parasites have led to implementation of selective therapy to reduce further development of resistance. It has been hypothesized that S. vulgaris could reoccur under these less intensive treatment circumstances. The aim with the present study was to evaluate the occurrence of S. vulgaris and the possible association with usage of selective therapy. A total of 42 horse farms in Denmark were evaluated for the presence of S. vulgaris using individual larval cultures. Farms were either using a selective therapy principle based on regular fecal egg counts from all horses, or they treated strategically without using fecal egg counts. A total of 662 horses were included in the study. Covariate information at the farm and horse level was collected using a questionnaire. The overall prevalence of S. vulgaris was 12.2% at the individual level and 64.3% at the farm level. Farms using selective therapy had horse and farm prevalences of 15.4% and 83.3%, respectively, while the corresponding results for farms not using selective therapy were 7.7% and 38.9%. These findings were found statistically significant at both the horse and the farm level. Stud farms using selective therapy were especially at risk, and occurrence of S. vulgaris was significantly associated with the most recent deworming occurring more than six months prior. The results suggest that a strict interpretation of the selective therapy regimen can be associated with an increased prevalence of S. vulgaris. This suggests that modifications of the parasite control programs could be considered on the studied farms, but it remains unknown to which extent this can be associated with increased health risks for infected horses.

Effects of praziquantel on experimental Schistosoma bovis infection in goats

The effect of praziquantel against experimental Schistosoma bovis infection in West African Dwarf goats was investigated. Thirty goats were exposed to 2000 cercariae each and 15 of those received a praziquantel treatment (60 mg kg-1) 13 weeks post-infection. One day, 1 week and 4 weeks post-treatment representative goats from each group were killed and worms were recovered by perfusion. For comparison, parasite-free control animals were monitored, some of which were given praziquantel. Every second week during the study, faecal samples were collected. The cure rate was 100% 1 day, 99.4% 1 week and 95.7% 4 weeks post-treatment. Tissue egg counts were significantly reduced (P < 0.001) 4 weeks post-treatment in all parts of the intestines, but not in the liver. Faecal egg counts were reduced by 84.1% 1 week and by 98.3% 3 weeks after treatment, the reduction being highly significant both 1 week 3 weeks after treatment (P < 0.001). Overall strong correlations between the number of worm pairs, tissue egg counts and the final faecal egg count were observed, indicating that the faecal egg counts during infection and following treatment can be used as a guideline for the pathology associated with the infection.

Trematode infections in freshwater snails and cattle from the Kafue wetlands of Zambia during a period of highest cattle–water contact

A total of 984 snails, comprising nine species, were collected from six areas in the Kafue wetlands between August and October 2003 to assess larval trematode infections. Of these, 135 (13.7%) were positive. Most trematode infections were recorded from Lymnaea natalensis (42.8%), which harboured four of the five morphologically different cercariae found. No trematodes were recovered from Bellamya capillata, Biomphalaria pfeifferi, Melanoides tuberculata, Physa acuta and Cleopatra nswendweensis. One snail (0.2%) of 416 Bulinus snails shed brevifurcate-apharyngeate distome cercariae while three (0.7%) shed amphistomes. Gymnocephalous and longifurcate-pharyngeate distome were the commonest types of cercariae recorded while xiphidiocercaria was the least common. The highest prevalence rates of F. gigantica (68.8%) and amphistomes (50.0%) in cattle (n = 101) were in Chiyasa while those in Kaleya had the lowest (9.1 and 18.2%, respectively). In most habitats, infections were recorded in both cattle and snails. Critical determinants of infection may have been the distance of settlements and/or cattle kraals, the number of animals in nearby homesteads and the presence of susceptible host snails. This study suggests that fascioliasis and amphistomiasis could be major constraints of cattle production in the Kafue wetlands because favourable factors were available to introduce and maintain the infections. It further provides a starting point for some comprehensive studies on snail-related aspects of transmission and snail host ecology in Zambia.

Prevalence of amphistomiasis and its association with Fasciola gigantica infections in Zambian cattle from communal grazing areas.

To estimate prevalence of amphistomiasis and its association with bovine Fasciola gigantica infections in Zambia, 709 faeces of cattle presented for slaughter from three major cattle rearing areas of Central, Southern and Western provinces were analysed. The prevalence rate of amphistomes was 51.6%. Egg counts per gram (EPG) of faeces ranged from 0 to 385 with a mean (+/- SEM) of 11.96 +/- 1.07. The origin of the cattle had a significant influence (P < 0.001) on the prevalence rate. Fasciola gigantica infections accounted for 46.7% of the cattle examined. The mean EPG count (+/- SEM) was 6.3 +/- 0.66 with a range of 0 to 223. A total of 34.6% were mixed infections while single Fasciola and amphistome infections represented 12.1% and 17.1%, respectively. Significantly more cattle (63.8%) were infected with either single or both trematode infections (P < 0.0001) than not. Mixed trematode infections were highest in the Southern province (80.0%) while the lowest were recorded in Central province (16.3%). A positive correlation (r(2) = 0.0428) was present in mixed infections. In order to minimize losses, epidemiology and cross-resistance of amphistomiasis and fascioliasis should be studied in different ecological regions of Zambia to formulate efficient control programmes.

Diversity and prevalence of metastrongyloid nematodes infecting the red panda (Ailurus fulgens) in European zoos.

Metastrongyloid induced pneumonia has been described sporadically in the red panda (Ailurus fulgens). Early descriptions in pandas recently imported to the USA from China involved parasites morphologically similar to Angiostrongylus spp. and Crenosomatidae. More recently, four cases of severe verminous pneumonia associated with Angiostrongylus vasorum have been reported from European zoos. A coprological survey of the red panda population within European zoos was conducted in 2008. Faecal samples from 115 pandas originating from 54 zoos were collected on 3 consecutive days. Using Baermann technique, 40 animals (35%) from 20 zoos (37%) were found to shed metastrongyloid first stage larvae (L(1)). Based on their morphology and size, the L(1) observed could be divided into three morphologically distinct types: (1) a Crenosoma sp. type (n=5, overall prevalence: 4.3%), (2) an A. vasorum type (n=3, 2.6%), and (3) an unidentified metastrongyloid species, similar to, but morphologically distinct from A. vasorum (n=32, 27.8%). Further confirmation of species identification was provided by PCR amplification and sequencing of the 18S rRNA gene, which confirmed three different species. The novel Crenosoma species was most genetically analogous to Crenosoma mephitidis and the unidentified metastrongyloid species was most similar to Stenurus minor and Torynurus convulutus. Routine and quarantine health care of red pandas in captivity should take account of the risk of Angiostrongylus and Crenosoma infection in endemic areas, but should also be cognisant of the widespread presence of an apparently less pathogenic species of lungworm. The identity of the two potentially novel species is subject to further work.

Real-time PCR evaluation of Strongylus vulgaris in horses on farms in Denmark and Central Kentucky

Strongyle parasites are ubiquitous in grazing horses, and the large strongyle Strongylus vulgaris is considered the most pathogenic helminth parasite of horses. Recent investigations have suggested an association between occurrence of this parasite and usage of selective therapy based on regular fecal egg counts. The established diagnostic method for S. vulgaris involves larval culture and subsequent morphological identification of third stage larvae under the microscope. Recently, a real-time PCR assay was developed and validated for the detection and semi-quantification of S. vulgaris eggs in equine fecal samples. The purposes of the present study were (a) to determine the presence of S. vulgaris by real-time PCR in Danish and American horses on farms using vastly different anthelmintic treatment regimens and (b) to evaluate the association between larval culture results and the PCR. A total of 991 horses representing 53 different horse farms in Denmark and Central Kentucky were studied. Fresh fecal samples were collected from all horses, and strongyle eggs retrieved for DNA extraction and subsequent real-time PCR analysis. Individual larval cultures were performed on the Danish part of the data set (663 horses on 42 farms). On the Danish farms, the S. vulgaris PCR prevalence was found to be 9.2% on farms not basing parasite control on fecal egg counts, and 14.1% on farms using selective therapy. No horses were PCR positive in the American part of the study (328 horses on 11 farms). Kappa-values indicated a moderate agreement between PCR and larval culture results, while McNemar tests revealed no statistical difference between the paired proportions. Significant associations were found between PCR cycle of threshold (Ct) value groups and larval culture counts. Results indicate that both diagnostic methods can be useful for determining the occurrence of S. vulgaris on horse farms, but that they both are affected by potential sources of error. The PCR results confirmed previous findings suggesting that S. vulgaris can reemerge under selective therapy regimens.

Acquired resistance in goats following a single primary Schistosoma bovis infection

The course of Schistosoma bovis infection was monitored in West African Dwarf Goats over a 34-week period following primary, experimental exposure (3000 cercariae/animal) and over a 17-week period following challenge exposure (2500 cercariae/animal) of goats harbouring 17-week old primary infection. For comparison, groups of challenge control and parasite-free control animals were monitored. Maximal egg excretion observed from week 8 to 12 following primary infection was accompanied by reduced weight gain, marked anaemia, hypoalbuminaemia and eosinophilia. These changes gradually diminished in parallel with decreasing egg excretion from week 14 onwards. Challenge infection induced neither additional egg excretion nor adverse effects in primary-infected animals. This was in contrast to challenge control animals which revealed the typical course of experimental schistosome infection including a peak of egg excretion, weight gain affection, and associated clinico-pathological changes. It was concluded that goats are capable of mounting an effective regulatory response to single primary S. bovis infection as well as to superimposed homologous challenge infection. Further elucidation of the regulatory response to S. bovis infection in goats are needed in order to determine its possible immunological background and epidemiological impact.

The impact of primary Schistosoma bovis infection on a subsequent challenge infection in goats.

Experimental primary and challenge Schistosoma bovis infections were studied in West African Dwarf goats, using clinicopathological and parasitological parameters. The experiment included 44 goats divided into 4 groups of which group A received primary infection, group B received primary and challenge infection, group C received a challenge control infection, and group D included noninfected controls. Primary infection (wk 0) and challenge infection (wk 16) both comprised exposure to 1,000 cercariae per goat, and necropsies took place 16, 22 and 32 wk following primary infection. Clinicopathological effects were moderate in all infected groups. Egg excretion became gradually reduced following peak levels during early primary infection, and egg excretion increased only marginally following challenge infection in the primary- and challenge-infection group. Similarly, challenge infection of primary-infected goats did not result in an increase in tissue egg counts. Worm recovery and tissue egg counts in primary-infected goats remained comparable throughout the experiment, and although evidence was obtained for a delay in maturation, challenge worm establishment was comparable with challenge-control worm establishment. An anti-fecundity effect is thus an essential component of the regulatory response to both primary and challenge S. bovis infection in the goats. However, it was also shown that the intrauterine egg count is an unreliable parameter for fecundity assessments.

Acquired resistance against Schistosoma bovis after single or repeated low-level primary infections in goats

Experimental Schistosoma bovis infections were studied in groups of six goats for 32 weeks. Two types of primary infections, a single exposure to 400 cercariae per goat or repeated (trickle) exposure to 200 cercariae per goat weekly for 10 weeks, were followed by a challenge infection with 2000 cercariae per goat in week 16 of the experiment. Periods of high faecal egg excretion were associated with reduced weight gain, anaemia, hypoalbuminaemia and blood eosinophilia; these changes gradually diminished with decreasing faecal egg excretion but never disappeared completely. The pathogenic effects of the trickle exposure exceeded those of the single primary exposure. After the challenge, the goats excreted few or no additional eggs and no additional clinicopathological changes were observed in the group previously exposed to a trickle infection. However, the primary single infection did not provide full protection against the effects of the challenge infection.

Experimental Schistosoma bovis infection in goats: the inflammatory response in the small intestine and liver in various phases of infection and reinfection.

In a histopathological study of goats experimentally infected with Schistosoma bovis, the characteristics of the inflammatory response in the small intestine and liver related to tissue egg counts and fecal egg excretion were compared between goats at different time periods of primary infection and of primary infection followed by challenge. At early patency, coinciding with increasing egg excretion, the intestinal lamina propria showed numerous intact schistosome eggs devoid of any inflammatory reaction, whereas egg-associated inflammatory foci in the intestine were significantly few. Later in primary infection and after challenge, intestinal changes were marked by a granulomatous anti-egg response, with only a minor component of eggs lacking inflammatory change, and were consistent with a reduction of egg transfer into the gut wall. Hepatocellular necrosis with eosinophil infiltration was pronounced only during the early patent stage. The results indicate that the early cascade of fecal egg excretion in caprine schistosomosis bovis is aided by a low degree of tissue reactivity to eggs in the intestine. They also lend support to previous findings indicating that an anti-fecundity effect is operative after exposure to challenge in this parasitic infection in goats.