Environmental contamination and transmission of Ascaris suum in Danish organic pig farms

Abstract

Background: Although Ascaris suum is the most common pig nematode, the on-farm transmission dynamics are not well described.

Methods: We performed a 1-year field study on five organic pig farms, mapping egg contamination levels in pens and pasture soil as well as faecal egg counts in starter pigs, finisher pigs, dry and lactating sows. The uppermost bedding material was sampled from three pen areas (resting, intermediate and latrine) of shallow and deep litter pens.

Results: Ascaris suum was found on all farms. Averaged across farm and season, the prevalence of A. suum was 48, 64, 28 and 15% in starters, finishers, dry and lactating sows, respectively. For starters and finishers, the prevalence varied with season increasing towards the end of the year when 83-96% of finishing pigs from each farm had fresh liver white spots. Farrowing pastures were contaminated with a mean of 78-171 larvated eggs/kg dry soil depending on farm, while pastures for starter pigs contained 290-5397 larvated eggs/kg dry soil. The concentration of eggs in soil was highest in the autumn. Indoors, all pen areas were contaminated with A. suum eggs at comparable levels for shallow and deep litter. Overall there were 106, 445 and 1331 eggs/g dry straw in the resting, intermediate and latrine areas, respectively. However, more eggs were undergoing development in resting areas (44%) compared to intermediate (33%) and latrine areas (13%). Irrespective of area, more eggs were undergoing development in the autumn, but overall there were very few fully developed (i.e., infective) eggs in the bedding material. Laboratory embryonation of eggs from the bedding material nevertheless revealed that an overall mean of 79% of the eggs were viable.

Conclusion: The organic pigs of all ages were continuously exposed to A. suum, but mainly younger animals were infected. Deep litter appeared to be a less important source of A. suum eggs than previously believed compared to shallow litter. Long-term pasture rotation to eliminate pasture contamination was not possible, and control programs should therefore include thorough cleaning indoors and composting/long-term storage of bedding material and manure to inactivate eggs and reduce transmission to pigs.

Fig. 1

Seasonal Ascaris suum prevalence in organic pigs. Mean percentage of all positive faecal samples (+ SEM) for 10–20 randomly selected individuals in each of four groups of pigs on five farms across four seasons

Fig. 2

Seasonal occurrence of Ascaris suum eggs in bedding material in relation to faecal egg counts. Number of eggs/g dry straw in resting, intermediate and latrine areas of pens (left Y-axis) and mean number of eggs/g faeces (right Y-axis) for starter and finisher pigs on five organic farms (A–E). Results are means of duplicate samples from each of two pens for each of four seasons, but it was not always possible to identify all three area types in each pen. Occasions of deworming are indicated by arrows

Fig. 3

Overall occurrences of Ascaris suum eggs in bedding material. Mean number of eggs/g dry straw (+ SEM) from three different areas of pens for starter or finisher pig pens on five organic farms. Results are means of duplicate samples from each of two pens across four seasons

Fig. 4

Seasonal development of Ascaris suum eggs in bedding material. Percentage of eggs at different stages of development in bedding material from resting (1), intermediate (2) and latrine areas (3) of pens with shallow litter (farms A, B and C) or deep litter (farms D and E). Results are means of duplicate samples from two pens for starter pigs (excluding Farm E) and two for finisher pigs for each of four seasons. NP denotes that a given area was not present

Fig. 5

Viability of Ascaris suum eggs from bedding material. Mean percentage (+ SEM) viable eggs (i.e., able to fully embryonate in vitro) isolated from bedding material from three areas of pig pens on five organic farms. Results are means of duplicate samples from each of two pens across four seasons. Eggs isolated from fresh faeces were embryonated for comparison (control)

Fig. 6

Ascaris suum eggs in soil from organic farms. Mean number of eggs/kg dry soil (+ SEM) on pastures on five farms (A–E). Results are based on duplicate samples from 1–3 pastures for each of three groups of pigs across four seasons. NP signifies the absence of a given pasture. Farm E results for dry and lactating sows are identical as they were kept on the same pasture