We hear that dogs need monthly heartworming tablets, and regular intestinal wormers, but have you ever wondered what is actually going on inside?
Heartworms are spread through mosquitos that carry the infective heartworm larvae. These larvae migrate from the bite wound through the dog’s body until they reach the heart and blood vessels of the lungs, a process that takes approximately six months. The larvae mature in the dog’s body — an adult heartworm can grow to be about 12 inches long. These adults reproduce and release immature heartworms, known as microfilariae, directly into the dog’s blood. When a mosquito bites an already infected dog, it may take in these microfilariae with the dog’s blood, and then pass on the infective heartworm larvae (the microfilariae develop once inside the mosquito) to another dog, thereby continuing the parasite’s life cycle and spreading the disease to the next host.
Risk factors associated with heartworm disease include residence in endemic regions, such as tropical areas, outdoor habitation, and lack of the proper prophylaxis to prevent heartworm infestation.
In initial treatment, most patients are hospitalized as they receive administration of an adulticide designed to kill the adult heartworms. The microfilariae in the body can be eliminated with a monthly prophylaxis, which can be administered at home. For more severe cases, such as dogs experiencing thromboembolic complications (in which a blood clot that has formed breaks loose and travels through the blood stream to clot another vessel), hospitalization may be necessary for a longer period of time.
In some cases, a surgical procedure may be necessary to remove adult worms from the right heart and pulmonary artery by way of the jugular vein. This procedure is recommended if the infestation consists of a high number of adult worms.
Worms in Dogs (and Cats)!
Why does the veterinarian want to check a stool sample? Dogs (and cats) are victims of several internal parasites frequently referred to as worms. The most common are the roundworms, hookworms, whipworms and tapeworms. Of these four only two are commonly seen in the stool with the unaided eye: roundworms and tapeworms.
Most worm infestations cause any or all of these symptoms: diarrhea, perhaps with blood; weight loss; dry hair; general poor appearance; and vomiting, perhaps with worms in the vomit. However, some infestations cause few or no symptoms; in fact some worm eggs or larvae can be dormant in the dog’s body and activated only in times of stress, or in the case of roundworms and hookworms, until the later stages of pregnancy when they activate and infest the soon-to-be-born puppies and kittens.
A large percentage of puppies (and kittens) are born with microscopically small roundworm, or ascarid, larvae in their tissues. The larvae is introduced to the developing pup (or kitten) right in the mother’s uterus — via migration through the mother’s tissues!
Roundworm larvae can also be transferred to the nursing pup or kitten from the mother’s milk. The larvae make their way to the intestinal tract where they can grow up to five inches in length. They start shedding eggs and try desperately to keep house in the small intestine of the pup (or kitten).
The eggs that the adult worms pass in the stool can now reinfest the animal or other dogs and cats if somehow the egg-bearing stool is eaten. When the worm eggs hatch, larvae are released internally to migrate to the animal’s lungs where the larvae (remember, the larvae are microscopic in size) are finally coughed up, swallowed, and finally grow up to adults in the small intestine.
Female roundworms can produce 200,000 eggs in just one day. These eggs are protected by a hard shell, which enables them to exist in soil for up to years. Puppies (and kuttens) with active roundworms in the intestines often have a pot-bellied appearance and poor growth. The worms may be seen in vomit or stool. If not treated in time, a severe infestation can cause death by intestinal blockage.
Roundworms don’t just affect young pups (or kittens), though. They can infest adult dogs and cats, too. However, as mentioned above, the larvae can encyst in body tissue of adult dogs and cats, remain dormant for periods of time, and can activate during the last stages of pregnancy to infest the puppies and kittens.
Worming the mother has no effect on the encysted larvae in the body tissues and cannot prevent the worms from infecting the newborn. Almost all wormers work only on the adult parasites in the intestinal tract.
This parasite is more often seen in dogs than cats. Adult whipworms, although seldom seen in the stool, look like tiny pieces of thread, with one end enlarged. They live in the cecum, the first section of the dog’s large intestine. Infestations are usually difficult to prove since the whipworms shed comparatively few eggs; so an examination of even several stool samples may not reveal the presence of whipworms.
If a dog is presented with chronic weight loss and passes stool that seems to have a covering of mucous (especially the last portion of stool the dog passes), and lives in a kennel situation or an area where whipworms are prevalent, the veterinarian may prescribe a whipworm medication based upon circumstantial evidence.
Although they seldom cause a dog’s death, whipworms are a real nuisance for the dog and can be a problem for the veterinarian to diagnose.
These are also much more common in dogs than in cats. They are very small, thin worms that fasten to the wall of the small intestine and suck blood. Dogs get hookworms from larval migration in the uterus, from contact with the larvae in stool-contaminated soil, or from ingesting the eggs after birth. As with roundworms, the hookworm larvae can also be transferred to the nursing pup from the mother’s milk.
A severe hookworm infestation can kill puppies, often making them severely anemic from the loss of blood to the hookworms’ vampire-like activities! Chronic hookworm infestation is a common cause of illness in older dogs, often demonstrated as poor stamina, feed efficiency and weight maintenance. Other signs include bloody diarrhea, weight loss, anemia, and progressive weakness. Diagnosis is made by examining the feces for eggs under a microscope.
The tapeworm is transmitted to dogs (and cats) that ingest fleas — as apparently fleas think tapeworm eggs are real tasty — or hunt and eat wildlife or rodents infested with tapeworms or fleas. If you were to see an entire tapeworm you would notice that they are arranged with a small head at one end and many tiny brick-like repeating segments making up the rest of the worm.
Tapeworms can reach 4 to 6 inches in length within the intestine. Each tapeworm may have as many as 90 segments (!), though it is the last segments in the chain that are released from the worm that can be seen in the stool or, as seen in the photo on the right, attached to the fur under the pet’s tail.
Many cases are diagnosed simply by seeing these tiny terminal segments attached to the pet’s fur around the anus or under the tail; they even move around a bit shortly after they are passed and before they dry up and look like little grains of rice or confetti. It also these segments of the tapeworm which contain the eggs.
*Animal Rescue QLD INC (ARQ) provides this information as general information and recommends checking with an authorized vet in your area, information contained in this post was accurate at 14-3-14. Use of this information is at owners risk and ARQ waives all liability to the full extent of the law.