Disease

Pig-Associated <em>Lawsonia intracellularis</em> in Various on-Farm Flies

Researchers at the University of Nottingham found that on many farms, one dominant farm isolate of L. intracellularis occurs within the pigs and the farm environment, including the insects most closely associated with the pigs. Of the insects found on pig farms, Musca domestica and Eristalis species flies have the most likely on-farm potential to carry and transmit L. intracellularis, they concluded.

1 December 2011

3 minute read

By: Jackie Linden

In a paper published recently in Journal of Swine Health from the American Association of Swine Veterinarians, Dr Steven McOrist of the University of Nottingham's School of Veterinary Medicine and Science in the UK and co-authors there and at University of Minnesota in the US reported their study to characterise the potential of pig-associated Diptera flies to carry L. intracellularis.

On 15 British farms, invertebrate communities were trap-collected (14 per year), counted, and sorted into species groups. Lawsonia serological tests were conducted and total DNA was extracted from pig faeces; DNA was also extracted from adult flies, pupae, and larvae samples and viscera of Blatta species. Each DNA sample was tested for L. intracellularis by polymerase chain reaction; positive samples were subtyped via specific variable number tandem repeat analysis.

The researcher found the pig-associated fly community was generally dominated by Musca domestica (house fly; n=13 farms) but on one farm each, Ophyra species (garbage fly) or Drosophila species (fruit fly) were dominant. Also noted were Muscina stabulans (false stable fly), Stomoxys calcitrans (stable fly), and Eristalis species (hover flies); Blatta orientalis cockroaches were noted on two farms.

Lawsonia infections were routinely detected in nursery pigs on 14 farms. On five of 12 Lawsonia-positive farms with Musca-dominant insects, Lawsonia DNA was detected within numerous flies (22 per cent to 75 per cent of fly samples from nursery pens). On two farms, larval forms of Eristalis from pen floors were also Lawsonia-positive. Subtyping indicated that the same Lawsonia isolate occurred within pigs and the pig-associated fly stages (Musca adults and Eristalis larvae). The DNA extracted from cockroach samples, and from other flies, was negative.

Musca and Eristalis flies have the greatest potential to carry and transmit L. intracellularis due to their pig-associated life cycle stages, concluded McOrist and co-authors.

Reference

McOrist, S., R. Blunt and C.J. Gebhart. 2010. Pig-associated Lawsonia intracellularis in various on-farm dipterous fly stages. J. Swine Health Prod. 19(5):277–283.