Ascarids are better known to pet owners and public health workers as roundworms. They are the most common parasite to intestinally infect dogs and cats.
While there are dozens of different types of roundworms found throughout North America, three different types commonly infect pets, and two of those types infect humans. The life cycles differ slightly in each of the three types of roundworms, but all pass through an egg, larvae and adult stage, with the adult parasite living in the small intestines of its host.
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Transport Host
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A transport host is an animal that carries an immature ascarid from one host to the next. Among the three types of roundworms commonly found in people and pets, small rodents serve as transport hosts of all three. With the Toxocara cati roundworm, the cat is the primary host, but beetles and earthworms can also be its transport hosts.
Transmission
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All three types of roundworms can be transmitted from transport host to primary host in similar ways.
The Toxascaris leonina roundworm, of which dogs, cats, foxes and wild carnivores are primary hosts, is usually transmitted when the primary host animal eats the transport host. For example, a cat that ate a mouse that was infected with the Toxascaris leonina roundworm would likely be infected with the parasite.
The Toxocara canis roundworm, of which the dog and fox are primary hosts, is transmitted in the same way as the Toxascaris leonina, but can also be transmitted from mother to puppy in the uterus or through the milk. This is one of the types of ascarids that can infect people.
With Toxocara cati, of which the cat is generally the primary host, transmission can occur when the animal eats a transport host or by a mother passing it to her kittens in her milk. Toxocara cati is the second type of ascarid that can infect people.
Eggs
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Once the eggs of the roundworm are transmitted to a primary host, the eggs hatch within the small intestines of the animal. Within the small intestines the larvae that hatches matures into adult ascarids.
With the Toxocara canis roundworm, the larvae may migrate to the respiratory system. The dog will cough up the larvae, swallow it and then the larvae will mature in the dog's intestines. This is common when in utero transmission occurs in puppies.
Reproduction
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Once the roundworms mature, they begin to reproduce. The adult female worm lays eggs that pass into the host animal's feces. The eggs will become ineffective if they are not ingested by a transport or primary host within three to six days.
Treatment
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To stop the lifecycle of ascarids once they have entered a primary host, a veterinarian can prescribe several different types of de-wormers for dogs and cats. These range from prescription medications to over-the-counter products.
To diagnose roundworms in people, your physician will ask you to provide a stool sample. Treatment usually consists of the medication Vermox, Antiminth or Albenza.
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