The adult Dipylidium caninum lives in the small intestine of the dog or cat, attached to the intestinal wall by several suckers as well as a structure called a rostellum which resembles a hat with hooks on it. Most people are confused about the size of a tapeworm because they only see its segments which are small; the entire tapeworm is usually 6 inches or more.
Once docked like a boat to the host intestinal wall, the tapeworm begins to grow a long tail. (The tapeworm’s body is basically a head segment to hold on with, a neck, and many tail segments). Each segment making up the tail is like a separate independent body, with an independent digestive system and reproductive tract. The tapeworm absorbs nutrients through its skin as the food being digested by the host flows past it. Older segments are pushed toward the tip of the tail as new segments are produced by the neckpiece. By the time a segment has reached the end of the tail, only the reproductive tract is left. When the segment drops off, it is basically just a sac of tapeworm eggs.
The sac, called a “proglottid,” is passed from the host’s rectum and out into the world, either on the host’s stool or on the host’s rear end. The segment is the size of a grain of rice and is able to move. Eventually the segment will dry and look more like a sesame seed. The sac breaks and tapeworm eggs are released. These eggs are not infectious to mammals. The tapeworm must reach a specific stage of development before it can infect a mammal and this stage comes much later.
Meanwhile, fleas living on the pet have been happily drinking the pet’s blood, mating, and laying eggs. The eggs drop off the pet and onto the ground where ever the pet goes with the largest number of flea eggs accumulating in areas where the pet tends to frequent. This will also be where tapeworm segments accumulate as well. The flea eggs hatch, releasing hungry flea larvae that eagerly begin to graze on dust, dandruff, and flea dirt. The flea larvae do not pay close attention to what they eat and innocently consume tapeworm eggs.
As the larval flea progresses in its development, the tapeworm inside it is also progressing in development. By the time the flea is an adult, the tapeworm is ready to infect a dog or cat. The young tapeworm is only infectious to its mammal host at this stage of its development. The flea goes about its usual business, namely sucking its host’s blood and reproducing when, to its horror, it is licked away by the host and swallowed.
Inside the host’s stomach, the flea’s body is digested away and the young tapeworm is released. It finds a nice spot to attach and the life cycle begins again. It takes 3 weeks from the time the flea is swallowed to the time tapeworm segments appear on the pet’s rear end or stool.
Controlling fleas is essential to prevent recurring infections with this species of tapeworm.
Ascarids are the most frequent worm parasite in dogs and cats. There are two species that commonly infect dogs: Toxocara canis and Toxascaris leonina. Adult roundworms live in the stomach and intestines and can grow to 7 inches (18 cm) long. A female may lay 200,000 eggs in a day. The eggs are protected by a hard shell. They are extremely hardy and can live for months or years in the soil.
There are four ways dogs can become infected with roundworms. Prenatal infection occurs when the larvae migrate through the placenta in utero. Almost all puppies are infected in this manner before birth. Mother’s milk can also transmit ascarids. In addition, puppies and adults can become infected by ingesting eggs in the soil. And finally, dogs can acquire the eggs by ingesting a transport or intermediate host, such as a mouse or other rodent.
The life cycle of T. canis in young puppies is as follows: Eggs entering through the puppy’s mouth hatch in her stomach. The larvae are carried to the lungs by the circulatory system. Here they break through the capillaries into the air sacs, sometimes causing bouts of coughing and gagging. Once in the lungs, the larvae crawl up the windpipe and are swallowed. Back in the intestines, the larvae develop into adult worms. The adults pass eggs that become infective in soil in three to four weeks.
Dogs older than 6 months develop an acquired resistance to ascarids. Few, if any, larvae complete the life cycle. Most come to rest in various body tissues, where they encyst. While encysted, they are protected against the dog’s antibodies and also the effects of most dewormers. During pregnancy, however, encysted larvae are activated and migrate to the placenta and mammary glands. Deworming the dam before pregnancy reduces the burden of migrating larvae but does not eliminate all puppy infestations because there are still encysted larvae in the mother’s body.
Ascarids rarely cause symptoms in adult dogs; in puppies older than 2 months, they usually produce only mild intermittent vomiting and diarrhea. Worms maybe found in the vomitus or passed in the stool. Typically, they look like white earthworms or strands of spaghetti that may be moving. In very young puppies, a heavy infestation can result in severe illness or even death. These puppies often fail to thrive, have a dull coat and a pot-bellied appearance, and are anemic and stunted in growth.