Traditionally, soil is viewed as a benign substance. It’s seen as a carrier of plant nutrients, a seed bed for growing crops or a place to grow feed for animals.
But sometimes soil carries more than nutrients and helpful microorganisms. There are diseases that can lurk unseen in soil for years, even decades, waiting to pounce on crops and livestock and cause losses for producers.
Prion diseases are one of the nastier things that can hide out in soil.
BSE is the most infamous of these conditions, which result from misfolded proteins and cause gradual neurological deterioration resulting in death.
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Other diseases in the family include scrapie, a condition seen in sheep, and chronic wasting disease, which is found in elk and deer.
While BSE outbreaks are usually associated with the feeding of infected animal material to other animals, infected soil is also one of the leading transmitters of prion diseases, according to Dr. Scott Napper, a senior research scientist at the Vaccine and Infectious Disease Organization in Saskatoon.
What’s more, prions can remain infectious in soil for a long time.
Napper pointed out that in one study, a sample was buried for three years and maintained 50 percent of its infectivity. Another study in Scotland found that scrapie could stay infectious in soil for 16 years.
“So certainly the span is definitely years, but probably into the decades,” said Napper.
Napper said the only thing for a producer to do once soil is contaminated with prions is to move their animals and decommission the sites.
“To put animals back on would be a virtual guarantee that they would contract a prion disease,” he said of elk ranchers whose herds were decimated by CWD.
Prions are notoriously tough and hold up to most decontamination procedures.
Napper pointed out that this caused significant challenges in a fully controlled lab environment and that he “couldn’t begin to imagine” how to go about decontaminating a farm site.
Clubroot is another disease that can quickly turn soil from an asset to an enemy. Similar to a fungus, clubroot is an organism called a protist. It occurs in soil as tiny resting spores and moves with the soil, either in the wind or in dirt stuck to a piece of equipment moving from field to field.
The spores move through water in the soil, entering the roots of susceptible plants like canola, camelina and mustard. Clubroot forms galls on roots, which impede plants’ ability to uptake water and nutrients.
Above ground, infected plants will show signs of yellowing, stunting and wilting.
Faye Dokken-Bouchard, plant disease specialist with Saskatchewan’s agriculture ministry, warned that producers who see these signs should dig up a few plants and check for the telltale galls on the roots.
From there, producers should send samples to either an agronomist or their provincial agriculture department to confirm the diagnosis.
Once it gets into a field, clubroot tends to stick around because there aren’t effective measures that can be used to eliminate it.
Dokken-Bouchard pointed to crop rotation as a key to containing clubroot.
“If there’s proper crop rotation, which means at least four years between canola crops, then we can prevent the spores building up,” she said.
Clubroot has yet to gain a foothold in Saskatchewan, but it has shown up in Alberta.
Limiting soil movement and making sure machinery purchased out of province is thoroughly cleaned are some ways that Dokken-Bouchard said producers can help keep clubroot from marching further east.
There are clubroot-tolerant seed varieties available, but these are not a guaranteed fix. Research continues on a fungicide.
Soil containing clostridials is another worry for livestock producers.
Clostridia diseases like anthrax, blackleg and tetanus are transmitted by bacterial spores that lie dormant in soil.
The different conditions caused by the bacteria all have different symptoms and affect different species.
Dr. Chris Clark of the Western College of Veterinary Medicine said “the one thing they all pretty much have in common is that they tend to cause sudden death.”
The other characteristic they have in common is soil.
Clark points out that the spores represent a survival mechanism of the bacteria when they have run out of resources and are waiting for their next host.
A simple way to imagine the spores is as “ a bacterial egg,” he said.
The spores are incredibly resilient. Clark said that in lab tests, anthrax spores can last in soil samples for up to 70 years.
While anthrax is probably the most famous of the clostridials because it can spread to humans, Clark notes that blackleg is generally the one that is most concerning to veterinarians.
There is no foolproof strategy to avoid having livestock come into contact with clostridials.
“There’s really nothing you can do per se to avoid them. If your animals are on the soil, they’re at risk,” said Clark.
With no way of dodging clostridials, vaccination remains the best option.
Clark notes that vaccinations with either a six, seven or eight way vaccine should be done in consultation with a veterinarian per manufacturer’s instructions.
He also warned that producers need to keep on top of their vaccination program after the initial two-stage vaccination with yearly follow ups.
The expense, lost time and lost animals caused by an outbreak can quickly eat up any savings a producer might get from skipping a year or two’s vaccinations.
“When (clostridials) raise their head is when people have stopped vaccinating,” said Clark.
