A whole new can of worms
July 3, 2014
From the desk of Dr. Voorheis
It is always a little uncomfortable to consider that intestinal parasitism exists in our pampered pets. We’d all like to think that is a more common problem in some other country, or that it happens to animals that aren’t as well cared for as yours. Well, to some extent that is true. It is helpful to remember however that there are a number of organisms whose only job is to survive, and your dog and cat are their hosts. The best way to combat the creatures that invade the gut is through knowledge. Knowing their life cycles and what you can do to keep your pet safe is key. So, what do I mean by intestinal parasites? In general, they come in two types; worms and protozoa. Let’s start with worms. To limit this discussion even further, I’m going to stick with the worms we see the most in our practice. Those would be Roundworms and Tapeworms. Neither is a dog or cat’s best friend. Pardon the graphic pictures, but I thought it a good idea to give examples so that you know what to watch for. Mind you, in the Tapeworm picture below, the worm is the small white rice looking object in the brown pile of ….well you are all familiar I’m sure.
Roundworms are common in dogs and cats. Two types affect dogs and two types affect cats. In dogs you have Toxacara canis and Toxascaris leonine and in cats you have Toxacara cati and Toxascaris leonine. Fancy names but at the end of the day, still parasites that are no good for your pets.
Dogs and cats can become infected by ingesting ova (worm eggs) or by using an intermediate host. Toxacara canis, the most common roundworm in the dog, is often obtained transplacentally from the mother. Yes, the puppies are actually born with them. Toxacaris cati uses transmammary passage (in mother’s milk). Toxascaris leonina can use an intermediate host.
The immature stages of roundworms migrate and can cause liver fibrosis and pulmonary lesions. Immature worms will encyst in “somatic tissues – i.e. body tissues” and won’t start migrating again until they are under the influence of certain pregnancy hormones. Then they will migrate to the uterus and into the fetus. The adult stages live in the small intestine and migrate against the flow of ingesta (nourishment taken in by mouth). They can cause inflammatory infiltrates in the wall of the intestine. Sometimes they will migrate into the stomach and are vomited up. A heavy worm load can cause intestinal obstruction, although this is uncommon.
This is the potential for an animal disease to cause disease in people. According to the Centers for Disease Control in Atlanta (CDC), roundworms make up part of a group of five parasitic diseases that are targeted for public health action. Close to 14% of the population of the United States have antibodies to roundworms indicating exposure. In people, the disease can cause one of two syndromes, ocular larval migrans and visceral larval migrans. There are 70 cases of ocular larval migrans per year in this country. They can cause permanent blindness. Children are at increased risk because they will sometime ingest dirt during outdoor play. Below is a diagram of the life cycle of the roundworm:
Diagnosis, treatment and prevention
Diagnosis is easy as ova are produced in large numbers and are readily found by fecal flotation. In some neonatal puppies the worms obtained transplacentally are in such high numbers that the puppies get sick before the worms mature enough to lay eggs.
The CDC recommends treatment of all puppies, regardless of positive or negative fecal results, beginning at age 2, 4, 6, and 8 weeks of age. Newborn puppies can be treated with fenbendazole (100 mg/kg x 3 days) – this treatment can be repeated in 2 to 3 weeks. High dose fenbendazole can be given daily (50 mg/kg/day) to the pregnant dog at day 40 of gestation and continued daily until two weeks post partum. For kittens, deworming at 6, 8 and 10 weeks of age is the proper protocol. Lastly, monthly treatment can be given to adult dogs, usually also given in the form of their heartworm preventative or monthly flea preventative. Two specific products come to mind. The first is Revolution which kills fleas, ticks and heartworm and is also effective against roundworms and scabies. The second product is Sentinel Spectrum which is a heartworm preventative and IGR + monthly deworming medication. For cats, use Revolution. No cat should be without it. I don’t want to be seen as putting one product up against another but Revolution is a very effective products for our cats and kittens and it is my responsibility to relay that information to my clients.
Here’s the bottom line on roundworms. It is a treatable zoonotic disease that we could and should do a much better job of getting rid of. Roundworms are a big part of the reason why a yearly fecal examination is so important.
Tapeworms are hands down the most common worm we deal with. I see dogs and cats infected with tapeworms every day. That is not an exaggeration – every day. Tapeworms have an indirect life cycle as the dog or cat is infected when it eats an infected intermediate host. Fleas and lice are intermediate hosts for D. caninum, wild animals such as rabbits are intermediate hosts of Taenia spp. Tapeworms are by far the worm that gets the most reaction from our clients. They are offensive to look at and nothing is more gross than cuddling with your favorite pet and ending up with motile tapeworm segments on your lap. Tapeworms rarely cause disease in our dogs and cats. The most common sign in infested dogs and cats is anal irritation (just another reason for our dogs to scoot on their behinds) associated with the shed segments crawling on the area. Tapeworms are usually diagnosed when the owner reports seeing segments (that are about the size of a motile grain of rice) either in the perineal area or in the feces. See picture above.
Treatment is with any drug or combination of drugs that contains praziquantal. Prevention of tapeworms involves controlling the intermediate hosts (i.e. fleas). Said another way… if your dog or cat has tapeworms, they have fleas. Period, end of story. So it cycles back to flea control. Remember my flea blog? It’s the circle of life.
There are three other intestinal worms to consider. These thre are far less common in Southern California. I have seen all three, but they are rare. They are Hookworms, Whipworms and Strongyloides. Whipworms should be investigated IF a dog has signs of colitis or large bowel disease. Whipworms may cause an unusual electrolyte disturbance that resembles that of Addison’s disease, but this is rare. Hookworms are not common in this part of the country. They can cause severe anemia as they are blood feeders. Strongyloides are also uncommon but should be looked for in puppies and kittens from pet stores and animal shelters. It too can cause large bowel signs.
Well, that’s enough gross worm business for today. Next time I will delve into one cell causes of parasitism such as Giardia, Coccidia and Tritrichomonas. Something to look forward to. (Gulp)
Until next time……