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Enzootic abortion (EAE) in sheep (Environmental Factors (Lambing…

- - - - Ensuring good hygiene during lambing time will help prevent the spread of bacteria
      - All sheep feed should be locked in vermin-proof containers - prevent contamination from cats and other vermin (NADIS, 2020)
        
        Because
        
        'A teaspoons of kitten feaces is enough to affect up to 700 sheep with T.gondii. (Hunt, 2012)
      - No pregnant women to come into contact with sheep (Entrican, 2001)
      - Risk of contamination of clothing and boots.
        
        Therefore
        
        Ensuring to wear gloves during lambing (Essig and Longbottom, 2015)
        
        Using disinfectants to clean the affected area, and work clothes should be washed in order to minimise the risk of transmission to humans (Essig and Longbottom, 2015)
      - Buying sheep from EAE free flocks prevent will help the control and prevention. (MSD Animal Health, 2020)
  - - - submit placentas and fetuses to veterinary or AHVLA centers for diagnosis of cause (XLvets, 2014)
        
        Flocks part of health schemes receive free investigation of abortion material as part of the annual fee paid (Mearns, 2007)
      - Dead animals must be taken to, or collected by an approved collector such as a kennel hunt, knacker or incinerator (Winter and Phythain, 2011)
    - - May not be able to keep closed herd
        
        So check the flock status on all sheep when buying in replacements such as 'EAE accredited flocks' as these are considered a safe source (Entrican et al., 2001) #
        
        In some cases this can be impractical and vaccination is the best approach - non-pregnant ewes can be vaccinated at any time until the 4 weeks before tupping (Entrican et al., 2001) #
        
        Memberships do these schemes have declined - increased availability to vaccines and premium received is no longer significant (Mearns, 2007)
    - - The aborted ewe could pass the infection onto the new lamb and therefore if the lamb is bred from it could lead to further abortions (NADIS, 2020)
      - Calculated cost of lamb lost in neonatal period is approximately £25 - although this figure does not consider the potential loss of earnings from lambs not going to be raised and sold (Gascoigne and Lovatt, 2017))
    - - Antibiotic use is not a cost-effective approach when vaccinations are available medium to long term (Lovatt et al., 2019) #
  - - - Evidence suggests this risk is minimal (Livingstone et al., 2009)
- - - - Only require to be vaccinated once
        
        vaccination cost £2-£3 per ewe is spread over the lifetime
      - Currently available vaccinations for C.abortus:
        
         MSD’s Enzovax
        
         CEVA’s Chlamydia
        
         Benchmark’s Mydiavac
        
        Witthdrawn in 2010. (Longbottom et al., 2013)
        
        Reintroduced and is an inactive vaccine so can be used on pregnant ewes (Benchmark's Animal Health, 2020)
      - Ewes to be vaccinated against C.abortus at least 4 weeks before going to ram
      - Estimates from reports suggest that approximately a third of replacement ewes are vaccinated against EAE and a fifth vaccinated against Toxoplasma (APHA, 2018)
      - 'Live Vaccines' could cause abortion. (Wheelhouose et al., 2010)
        
        Absent 'inactive vaccines' mean the live vaccines are most effective way to prevent EAE. (Stuen and Longbottom, 2011)
        
        Although 1B Vaccine reduces abortion and shedding in Ovines - doesn't confer complete protection: Study showed evidence of 1B vaccine in aborted placenta (Wheelhouse et al,. 2010))
        
        14 postitive cases of C.abortus out of 35 vaccinated flocks
        
        Does not completely prove vaccine was the cause of abortion, although no other major abortifacients were identified during screening (Wheelhouse et al., 2010)
      - C.abortus Vaccines only fully assessed for prophylactic used (Chalmers et al., 1997)
      - T.gondii vaccination - provides excellent immunity and should be given at least 3 weeks prior to start of breeding season (NADIS, 2020)
        
        Costs approximately £3 per ewe - but as a single vaccination that provides lifetime immunity = 50-60 pence per pregnancy (NADIS, 2020)
        
        1 2ml injection can induce immunity against T.gondii for a minimum of 18 months (Buxton and Innes, 1995)
    - - Ewes given a daily dose of 16.8 or 27.9mg of monensin resulted in fewer abortions from T.gondii compared to those not treated (Buxton et al., 1988)
  - - - Reduces the risk of other ewes in the group aborting
      - Is an emergency measure
        
        Placental damage cannot be reversed - ewes may carry closer to term but are still weak with high mortality rates (NADIS, 2020)
      - If placental infection has already begun, a second injection after 2 weeks can help to reduce further losses (Entrican et al., 2001)
    - - Some farmers are unnecessarily giving whole-flock antibiotics yearly, potentially contributing to antibiotic resistance
      - An unpublished survey suggested that it is common for approximately 10 percent of sheep farmers to undertake routine prohylactic treatment of all ewes in late pregnancy to control EAE. (Lovatt et al., 2019)
- - - - Longbottom et al., (2012) found that where EAE was diagnosed in a flock other abortificients also diagnosed.
      - Toxoplasmosis = parasitic infection of Toxoplasma gondii
        
        Highest number of barren sheep is youngest age group (NADIS, 2020)
        
        T. gondii is a source on endemic loss for sheep farmers and dangerous for consumers - particularly pregnant women (Dubey, 2009; Innes et al., 2009)
        
        sheep that are kept on pastures are at risk of infection due to environmental contamination with sporulated oocysts (Cenci-Goga et al., 2013)
        
        if oocysts are heavily contaminating the environment, the infection prevalence can be higher than 90% (Samra et al., 2007)
        
        can cause abortion at earlier stages during pregnancy (Sarginson, 2003)
        
        Oocytes of T.gondii are only formed in cats and shed in faeces (Williams and Donovan, 2009) #
      - Campylobacter - Happens in intensively managed flocks
        
        Leads to heavy contamination and unhygienic environments during late gestation (NADIS, 2020)
  - - - EAE-affected ewes develop immunity post-infection that prevents future abortions from C.abortus (Sammin et al., 2005)
  - - - Lowland flocks typically have a higher sheep-sheep contact rate compared to hill flocks (Longbottom et al., 2012) #
- - - - C. abortus rarely affects humans and there are no more than 1-2 cases per year. (Public Health England, 2008) # #
      - Toxoplamsa gondii is the most widespread zoonoses in the world with a disease prevalence of 10-30% in humans (Lopes et al., 2013)
        
        currently there is no vaccine to prevent T.gondii in humans (Dubey, 2008)
  - - - Evidence of pregnant women with severe infections after contact with EAE sheep and placentas: Sporadic abortions, still births and septicemia (Meijer et al., 2004; Walder et al., 2005)