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Heavy rain, lambs, and leptospirosis

A warm, very wet summer and autumn certainly brings with it an abundance of feed for grazing livestock and nearly all the stock we are seeing is in excellent condition.

For sheep farmers however such conditions can come with many headaches. We are hearing reports of late cases of fly strike, salmonellosis, a lingering high spore count which has prolonged the facial eczema season and severe worm challenge. Gribbles veterinary pathology has also reported an increase in the number of cases of leptospirosis in lambs.

Earlier this month I was called to investigate a case which did indeed turn out to be an outbreak of leptospirosis. A unit load of lambs was purchased and trucked for approximately three hours. Upon arrival they were quarantine drenched and turned out. The following day there were two dead and several starting to look sick. On day two a few more were found dead at which point I was asked to investigate, carried out a post mortem, took some samples, and confirmed a diagnosis of leptospirosis. Once we had confirmed that leptospirosis was the issue the mob was vaccinated and treated with streptomycin. By the time this was completed approximately 40 lambs from the mob of 650 had died and a significant number were still looking seedy. The deaths slowed down about 10 days after vaccination/treatment but there have been ongoing losses. The direct measurable costs in this outbreak are approximately $12,000 to 15,000 but the mob as a whole will have taken a check which is harder to quantify.

Background
Leptospirosis is a globally important disease which can affect all mammalian species as well as humans, caused by pathogenic species of Leptospira. These slender, helical, motile, spirochete bacteria, harbour in the kidneys of chronically infected, carrier animals and are shed intermittently in their urine into the environment. Animal reservoirs of the disease include livestock as well as wildlife, typically rodents. In addition, leptospires survive in wet soils, leading to contamination of surface water following heavy rainfall and flooding.

Lepto pomona outbreaks in lambs
The typical picture is sudden deaths and malaise in several lambs in a mob, with possibly 10 to 20 dead lambs. On opening an affected lamb carcase (usually in good body condition), the key necropsy findings are marked jaundice of the omental fat, generalised carcase pallor, yellow/brown liver, dark urine, and dark swollen kidneys.

Similar symptoms can be seen with a range of other conditions including:

  • Copper, zinc toxicity, chronic or acute. There is usually a history of administration.
  • Brassica toxicities – grazing history.
  • Mycoplasma ovis infection – parasites in RBCs.
  • Bacillary haemoglobinuria – one of the clostridial diseases covered by 5-in-1 vaccination.
  • Facial eczema – heavy sporidesmin challenge can directly cause acute haemolysis in some cases.

Pathogenesis

Outbreaks of leptospirosis affecting weaned lambs occur after exceptionally heavy summer rainfall, causing accumulation of surface water to which stock have access. Transmission can be direct through infected urine splashing and post-abortion discharges but indirect transmission through contamination of soil and water sources via infected urine is more likely for grazing lambs.

Leptospires penetrate exposed mucous membranes or through abraded or water softened skin and then disseminate throughout the body. In many situations the infection will be sub clinical and can only be detected by serology or at necropsy/slaughter.

The acute and often severe form of the disease occurs during the phase when the leptospires are in the bloodstream, particularly in young animals, as has been observed in the outbreaks of  leptospirosis (serovar Pomona) in grazing lambs this season. In these cases, the anaemia is initially due to the production of the haemolysin toxin and later is caused by an antibody mediated reaction against leptospiral antigen-coated red blood cells. Jaundice may result from both the haemolysis as well as toxic and necrotic liver damage.

Prompt treatment of sick lambs with injections of Streptomycin is reported to be highly effective and good protection is afforded by Leptospira vaccination which is recommended in high-risk situations.

Don’t forget that leptospirosis is an important Zoonotic disease so if you are dealing with an outbreak, please exercise extreme caution. Wear gloves or at least cover up any cuts and scratches, avoid urine splashes and wash hands after dealing with a mob.

Your dogs are also susceptible to lepto so ensure they are vaccinated and make sure they don’t have access to dead carcasses.

On a final note…

One thing that this case did highlight was the value of a post mortem. Following a telephone conversation with the client, in the case mentioned above, I was of the opinion that this was an outbreak of pneumonia caused by the stress of trucking. It was not until the post mortem was carried out that we knew what we were dealing with and put a plan in place.

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