Day 2: Parasites, Parasites, and...MORE Parasites!

Ok, I'm going to forewarn you right now...if you are easily disgusted, you might not want to read this blog post!

As you might have guessed, today I read about the lovely and wonderful things we call parasites! I hope you can sense my sarcasm.  Horses are hosts for about 150 different types of parasites, but I just read about the 6 most common ones that I will likely see in the wild horses. The most common internal parasites in horses are helminths (worms), arthropods (insects), and protozoa (microscopic organisms). Horses are most frequently affected by intestinal parasites and less so by respiratory, musculoskeletal, or central nervous system ones. Parasites can vary greatly in size, the smallest protozoa being about 1/4000 of an inch and the biggest tapeworm being around 2.5 feet long!

Different parasites have different life cycles, but the basic cycle is that the eggs hatch, develop into larvae, migrate through the body of the host (migration causes the most damage), and mature into adults that lay from hundreds of thousands to millions of eggs per day. The most common way for a horse to get infected is through eating grass or hay that is contaminated with manure that contains the eggs or larvae.

The six parasites that I read about today are Large Strongyles, Small Strongyles, Ascarids, Stomach Worms, Tapeworms, and Bots, some of which are the most serious parasites a horse can get and can even result in death if not treated properly.

Large Strongyles
Large Strongyles are commonly called bloodworms or red worms and are one of the most harmful parasites. Grazing horses consume the hatched larvae, which then mature in the intestinal tract and burrow out into blood vessels where they migrate throughout the various organs and eventually back into the intestine. This migration causes extensive damage to the lining of blood vessels, as the larvae cause aneurisms (weakened areas) in the vessel wall, resulting in blood clotting. Sometimes this blood clotting completely blocks blood flow, which then results in dead tissue. Symptoms of bloodworms include fever, loss of appetite, weight loss, and constipation or diarrhea. Notice that one of the symptoms (which will reoccur a lot) is weight loss, which pertains to one of my goals! Body condition score (BCS) is the relative proportion of muscle to fat, and in North Carolina I will be evaluating how parasites affect a horse's BCS, so I will be able to put this knowledge into use to achieve one of my goals.

Small Strongyles
Small Strongyles have the same life cycle as bloodworms but differ in that they do not migrate outside of the intestinal tissues, which is where most of the damage is created with bloodworms. However, small strongyle larvae have the ability to become encysted (enclosed as if in a cyst) in the large intestine for a period of time, waiting for the proper conditions to emerge again. This is a huge issue when trying to treat Small Strongyles because during this time, the larvae are not susceptible to most dewormers. Symptoms include loss of condition, weight loss, poor coat condition, and slow growth; Small Strongyles can also be fatal if there are a large number of worms.

Ascarids
In my opinion, these are the most disgusting, so feel free to skip this section if you would like! Ascarids' average size is 6-12 inches long! Not only that, but there can be hundreds of them in a horse's small intestine at one time, which (as I'm sure you can imagine) can adversely affect its nutrition. They can either create blockage in the intestine or migrate through the lungs, which can cause pneumonia in addition to the other effects, which are colic, coughing, diarrhea, poor growth, rough hair coats, chronic respiratory problems, and sometimes death. The most disgusting part of it all, though, is that young worms travel up to the mouth to be swallowed a second time...YUCK! I wonder if I'll see any of these in North Carolina.

Stomach Worms
Horses do not usually consume stomach worm larvae directly, but first fly larvae in manure of horses ingest the larvae of the stomach worms. Then once the fly matures, it either deposits the worm larvae in the lips of the horse or the horse ingests the fly. However, much more serious than internal stomach worms are the lesions that result from deposition of larvae at sites where flies sometimes feed, such as the corner of the eye or in a skin wound. This causes summer sores, which are an inflammatory response characterized by fleshy masses that bleed easily.

Tapeworms
The most common species of tapeworms is about 2 inches in length, but one of the less common species can reach up to 30 inches long! Like Stomach Worms, Tapeworms are not consumed directly by the horse; mites in the pasture consume eggs from the feces of infected horses. Grazing horses then swallow the mites and become infected, which causes symptoms such as weight loss, diarrhea, and sometimes colic.

Bots
Last (but not least!) are Bots, which are larvae of the botfly. Botflies lay eggs on the hair of various parts of horses, particularly around the chest, forelegs, throat, and nose. Horses then lick the infected areas, and the larvae hatch and enter the horse's mouth, settling into the tissues of the gums, cheek, and tongue. After a month, the larvae migrate and attach to the stomach lining, causing irritation and interference with digestion.

See, I told you parasites were lovely and wonderful! While it is fun researching all day, I am excited to start putting my knowledge to use! It'll be exciting to see if I will actually be able to identify these parasites in the wild horses' fecal examples.