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BIONÆR-Bionæringsprogram

HESTEFORSK Selektiv behandling mot Strongylus vulgaris - risikoer og muligheter H1547-097

Awarded: NOK 2.1 mill.

Resistance to dewormers is a threat to equine health and welfare. To slow down the development of resistance restrictive use has been adopted. Current recommendations for deworming include selective treatment of horses shedding high numbers of parasite eggs. However, in recent years veterinarians have observed an increase in parasite-related injuries, and routine diagnostic analyses suggest increasing prevalence of Strongylus vulgaris (the large bloodworm), which is the most pathogenic parasite of horses. This Swedish-Norwegian collaboration aimed to investigate if selective deworming can be linked to an increase in the S. vulgaris prevalence. We also aimed to establish the correlation between S. vulgaris infection and parasite-related damages. Lastly, we evaluated the effect of grazing hygienic measures as a tool to reduce the parasite burden and corresponding need for deworming. Faeces and questionnaire data for the Norwegian prevalence study were collected in 2017 and 2018. We invited horse owners by direct mail, and the study was announced on the Facebook page of the Norwegian Veterinary Institute and the webpages of Norwegian equine breed organisations. Only farms with more than five horses that did not deworm within 6 months before sampling were included. We collected samples from 56 farms and 435 horses covering all parts of Norway and various types of farm management. Based on faecal egg counts, intestinal parasites were found in all farms with egg counts ranging between 0 and 3921 eggs per g of faeces. Of the individual horses, 63.4% excreted parasite eggs. S. vulgaris eggs were found in 27.3% of the farms and 3.5% of the individual horses. However, we found a poor correlation between faecal egg counts and the presence of parasites in the faecal cultures. Therefore, molecular analyses of parasite eggs in the faecal samples are ongoing.The tapeworm, A. perfoliata, was detected in 14 of 56 farms corresponding to a farm prevalence of 25% and an individual prevalence of 6.7%. This parasite is usually considered relatively non-pathogenic, but there is increasing evidence that heavy infections may be linked to intestinal obstruction and colic. Dewormers belonging to the group of macrocyclic lactones were used in 84.7% of the Norwegian horse farms. Frequent use of these drugs without any preceding parasitic diagnosis may explain the relatively low prevalence of S. vulgaris in Norway compared to Sweden where 61% of the farms and 28% of the individual horses tested positive for S. vulgaris. Correlation between S. vulgaris infection and disease was investigated in the second part of our project. Unfortunately, recurring outbreaks of salmonellosis in the horse clinic at the Norwegian University of Life Sciences prevented the completion of the study in Norway, as we were only able to obtain samples from 69 horses. In Sweden, however, 137 cases and 137 controls with no clinical signs were studied. No associations were found between colic and detection of S. vulgaris by blood test, faecal egg count or larval cultures. Of the horses that had abdominal surgery and/or were euthanized, parasitic injuries were found in three cases with S. vulgaris associated severe damage of the colon. Interestingly, these cases excreted no strongyle eggs but tested positive for S. vulgaris by blood test. Peritonitis was linked with serological detection of S. vulgaris. The third part of our study tested if regular removal of faeces reduces the number of strongyles on pasture. This study was conducted in Sweden and demonstrated that the number of parasites was considerably lower in samples collected from pasture where faeces was removed regularly. Dung removal could thus be a useful alternative/supplement to deworming. In conclusion, 28% of the Swedish horses and 61% of the farms tested positive for S. vulgaris, indicating a threefold increase since 1999. In Norway, the corresponding prevalences were 3.5% and 27.3%, respectively. However, firm conclusions regarding the situation in Norway cannot be made until the final molecular results are available in Jan. 2020. We observed a 2.9 increased risk of S. vulgaris infection on farms that based deworming on faecal egg counts only as compared to farms that used egg counts plus larval cultures or dewormed regularly, 1-4 times per year, without prior diagnosis. We found no association between the prevalence of S. vulgaris and egg excretion levels, but high prevalence (25%) of S. vulgaris in horses shedding less than 150 EPG. Horses with low egg counts that are left untreated could be an essential source of S. vulgaris infection and might be an important reason for the increased prevalence of S. vulgaris in Sweden. Faecal removal effectively reduced the parasite numbers on pasture and may be useful to reduce the contamination levels on the pastures. Finally, S. vulgaris needs to be monitored continuously and should be taken into careful consideration when the deworming frequency is reduced.

We report increased prevalence of S. vulgaris in Swedish horses, with a potentially negative impact on equine health. In contrast, our preliminary results suggest a much lower prevalence of S.vulgaris in Norway, probably linked to frequent deworming without previous coproscopic analysis. Yet, routine anthelmintic treatments several times per year is no solution since that would likely accelerate the spread of multidrug resistance. Instead, we recommend selective anthelmintic treatment and S. vulgaris diagnostic testing in the spring. Additionally, collection of faeces from the grazing areas twice weekly should be practiced. Primo 2020, we will invite stakeholders to a roundtable discussion at SLU aiming at reaching consensus and formulate common recommendations. The ambition is to provide veterinary surgeons and horse owners in Scandinavia with up to date information on worm control practices that will prevent clinical disease while minimising selection pressure for resistance.

Resistensutveckling mot avmaskningsmedel är ett hot mot hästars hälsa. I likhet med antibiotika är det nödvändigt att vara restriktiv med avmaskningsmedel för att kunna bevara effekten. Selektiv avmaskning rekommenderas därför sedan ungefär tio år men klinikveterinärer och patologer har observerat en ökning av parasitrelaterade skador under de senaste åren. Data från SVA indikerar samtidigt en ökad förekomst av stor blodmask. Syftet med det här norsk-svenska projektet är dels att utveckla diagnostiken av hästens stora och små blodmaskar och dels undersöka om selektiv avmaskning kan kopplas till en ökad parasitförekomst och parasitrelaterade skador. För första gången i Skandinavien kommer vi även att mäta effekten av beteshygieniska åtgärder som komplement till selektiv avmaskning. Det är avgörande för framtiden att man inom hästnäringen tillämpar långsiktigt hållbara rutiner för parasitkontroll utan att det samtidigt leder till ökade parasitskador.

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BIONÆR-Bionæringsprogram