The Evolution of Parasitism
The Classic Parasitized Horse
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This is what most people envision when they think of a parasitized horse. Horses that are heavily parasitized – like this one – tend to look emaciated, potbellied and unhealthy. The good news is that this is an old picture. Today, we rarely see this extreme condition except in situations of abuse.
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Today’s Parasitized Horse
Today’s parasitized horses seem healthy and athletically able. They may or may not have any outward symptoms of parasitism. Even though you can’t see it, however, these horses may be so severely parasitized that both performance and health are compromised. The truth is, what you can’t see may be costing both you and your horse.
As Horse Populations Grew, Parasitism Increased
So why does parasite damage in the modern horse seem so different from years ago? Horses and parasites have co-existed quite well for 50 million years with no intervention from man. Although we commonly regard parasites as useless and destructive, they play an important, positive role in the overall ecosystem.
Parasites serve as population-control mechanisms. When horse populations get too big for the ecosystem, parasites kill some of the horses. Though it is not a pleasant thought, parasites can help subtly monitor and effectively maintain a population at an appropriate level.
An Endangered Species, the Rural Horse
Parasites are an increasing problem in the modern horse because domestic horses are typically maintained in a manner that is vastly different from their “natural” environment. Even 30 to 40 years ago, horses were kept in predominantly rural environments. That’s not the case today.
The Urbanized Horse
Now most horses are kept on small acreages around major metropolitan areas. We have made the horse an urban dweller. Domesticated horses are housed close to one another, frequently in climates that are extremely favorable for parasite development. Although small paddocks and stables benefit the horse in terms of comfort, food quality and general health, the prevalence of parasites under such conditions and, therefore, their impact on horses, are magnified beyond that which would occur naturally.
For this reason, parasitism is a constant threat to the health and life of domesticated horses. Without adequate and consistent parasite control, horses are vulnerable to the potentially fatal effects of parasitism.
50 Million Years of Development
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Let’s take a look at how horses and horse parasites have evolved over time. As the horse was developing from mesohippus – a small, migratory herbivore, just 15 inches tall – to Equus caballus, the modern-day horse, equine parasites were evolving in parallel, developing life cycles that would function under the conditions endured by the early horse.
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The Genetic Cradle of the Light Horse
To fully appreciate the horse/parasite relationship, we have to understand where horses and parasites originated and how they developed. The “light” horse, as we know it, developed in the last 50 million years in North Africa, the Arabian Peninsula and Central Asia. This region is the genetic cradle of the horse. In this harsh, arid climate with sparse vegetation, horses typically migrated about 25 miles a day looking for food and water. It was under these rugged conditions that the horse – and its parasites – developed.
Environmental Conditions in the United States
In the United States, conditions are very favorable – compared to what these parasites have learned to adapt to and survive in.
To learn more about the Evolution of Parasitism, click here.
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