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7 recent advances in understanding Lawsonia


The gram-negative bacteria Lawsonia intracellularis has been known as an important agent responsible for economic losses in the swine business for many years, as the bacteria causes ileitis. Yet scientists continue to discover new insights about the bacteria, which in turn can help to better prepare for it, e.g. by implementing routine control measures.


BY OLIVER DURAN, BOEHRINGER-INGELHEIM ANIMAL HEALTH T


he agent responsible for ileitis, Lawsonia intracellu- laris (Li) is an intracellular gram-negative bacteria that infects the enterocytes (the cells lining the in- testine) causing damage primarily to the small in-


testine but also the large intestine. Which are some of the more recent discoveries about the bacteria?


1. Lawsonia is present in most European herds A recent survey of 144 European pig herds that had suffered a diarrhoea outbreak in the previous year carried out in Denmark, France, Germany, the Netherlands, Spain, and UK. The paper has confirmed earlier studies showing widespread infection, with over 90% of herds exposed to Li. Evidence using two tests, qPCR and ELISA confirmed those findings. The prevalence ranged from 100% of herds in the UK to 79% in France but these differences were not statistical. There were some differences between countries; herds in Denmark had a higher detection rate based on serology. While in most herds the detection of Li was concentrated in grow-finish age pigs, in Denmark the highest rates of detection were in the nursery.


2. Subclinical pigs can easily infect pen mates Investigating the transmission dynamics of Li using a seeder pig model has shown infection can spread to as many as 18 (62%) pigs within a pen due to the introduction of one infect- ed animal within a 38 day period. Importantly, this spread caused a reduction in average daily gain (ADG) for the whole pen, when compared to uninfected controls. How did the researchers find that out? The seeder pig model was set up to learn about on farm transmission dynamics of Li. Fernando Leite and colleagues designed a study with three


32 ▶ GUT HEALTH | DECEMBER 2020


treatment groups to assess Li transmission: • Group 1, one seeder animal to 29 sentinel animals; • Group 2, two seeder animals to 28 sentinel animals; • Group 3, control with only non-infected pigs. Each treatment group was housed in a separate room and pen with 0.8 m2


(2.5 ft2 ) per animal. Sentinel animals were


monitored for 38 days of exposure to seeder pigs. Faecal shedding of Li was tested by qPCR twice weekly for the length of the study. Shedding of Li was first detected in senti- nels 14 days after introduction of the seeder pigs. In group 1, 62% (18 of 29) shed Li and shedding peaked at 38 days, while in group 2, 86% (24 of 28) of sentinel pigs shed Li at least once during the stud, peaking at day 21. Within pen transmission is variable depending on the number of seeder pigs and this changes how fast the infection spreads. In an- other transmission rate study in non-vaccinated pigs, one in- fectious pig (shedding >103


bacteria/gram of faeces) was


able to transmit Li to three susceptible pigs per week. So if pigs from infected and naïve flows would be co-mingled at the end of the nursery, infected pigs would triplicate within the population every week.


3. Vaccination reduces Lawsonia transmission To understand the impact of vaccination on the transmission of Li, researchers at the University of Minnesota compared both the oral and intramuscular vaccine with non-vaccinated controls. Transmission rates were significantly reduced in both vaccinated groups. The model used to predict transmission over time also showed a shorter period of faecal shedding of Lawsonia in both vaccinated groups (Oral 6.3, IM 8.3, non-vac- cinated 11.2 weeks). The shedding was 43.3% shorter in the orally vaccinated pigs compared to the unvaccinated animals.


4. Local immunity is critical Better tools are available to understand the immunity to Li. As the infection is restricted to the gut it is expected that local, or mucosal immunity is critical. The local humoral immune response (IgA antibodies) and elevated secretion of suppressive cytokines by immune cells in the intestinal wall (Cell Mediated Immunity – CMI) play an important role in protection by controlling inflammation and restoration of the intestinal cell wall. Therefore an ideal vaccine should be able to elicit a balanced immune response where both CMI and local humoral immunity to control ileitis.


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