Worms

roundworms, hookworms, tapeworms, whipworms, and heartworms – are parasites that can live inside and rob your dog or cat of vital nutrients. Worms can cause anemia (low levels of red blood cells), lethargy, poor appetite, and even death. Pet owners should ask their veterinarians which parasites to watch for because worms have various geographical distributions (e.g., heartworm is more common among cats in warmer climates). Pet owners can take preventative measures against particular parasites. Medications are commonly used to prevent most worm infections.

Roundworms

Roundworm infection is transmitted through ingestion of its eggs in an infected rodent, infected soil, or milk from an infected mother. The eggs hatch into larvae in the stomach, and the larvae travel to the small intestine where they mature into adults. The adults lay eggs, which pass out of the pet in its feces. The worms can also be transmitted from mother to puppies or kittens in utero.

If humans somehow ingest roundworm eggs, the eggs can develop into an infection. It is important to wash hands after handling dog feces. Children should not be allowed to play on soil where dogs defecate.

Symptoms typically include the following:

Bloated belly
Blood or mucus in the stool
Diarrhea
Lethargy
Loss of appetite
Vomiting
Severe infection can create intestinal obstruction and cause death in puppies and kittens.

Roundworm is diagnosed by examining the feces for the presence of eggs.

Several oral medications are available for the treatment of roundworms. Pet owners should discuss the options with their veterinarian. Treatment generally requires more than a single dose.

Pet owners also should ask their veterinarian about the incidence of roundworm in their geographical area and whether monthly preventative medication (e.g., Sentinel®, Heartgard Plus®) is necessary.

Hookworms

Hookworms are the most common canine intestinal parasite in the United States, infecting nearly 20% of all dogs. Hookworms attach to a dog's intestinal lining with hooklike teeth.

Hookworm infection is transmitted by ingesting the infective larvae (which usually live in soil) or by the larvae attaching to and burrowing through the dog's skin. Once inside the dog's body, larvae travel to the small intestine, mature, mate, and lay eggs. The eggs pass into the soil through the dog's feces. Hookworm can also be transmitted through a nursing mother's milk.

Since hookworms can penetrate skin tissue, it is possible for people to pick up the larvae when walking barefoot on infected soil. Children should not be allowed to play in areas where dogs defecate.

Symptoms of hookworm infection include the following:

Anemia (severe cases)
Diarrhea
Diminished strength and vitality.
The worms feed on the host's blood. Puppies can develop life-threatening anemia from blood loss even before eggs are detectable in the feces.

Hookworm disease is diagnosed by examining the feces for eggs.

Several oral medications are available for the treatment of hookworms. Several preventative monthly medications are also available. Pet owners should discuss the options with their veterinarian.

Whipworms

Whipworm infection causes bloody diarrhea, weight loss, anemia and dehydration, but diagnosis is very difficult and may require several exams. Symptoms include diarrhea, abdominal pain and mucus-laden stools streaked with blood. A large number of worms (more than 2,000 in some cases) can cause anemia.

Whipworms, 1.75 to 3 inches long, reside in the large intestine and cecum. Using its mouth as a spear-like sword, the whipworm slashes and punctures the intestine and then feeds on the released blood and tissue fluids.

The most common method of whipworm transmission is through the feces of dogs, but it is also suspected that they may be transmitted through soil. The eggs that pass through the feces can be swallowed unhatched by a healthy dog, where they will hatch inside. Whipworm is difficult to control outside the dog. Whipworm eggs pass into the soil, where they can survive for years under the most severe weather conditions. Whipworm eggs are virtually impossible to attack chemically (the ova may be absent from feces in many infected dogs).

Adult whipworms live in the cecum of dogs, where they lay eggs. The eggs are released with the dog's feces, where they then dwell. The larvae develop inside the eggs. Whipworm Transmission and Growth as the larvae grow within the eggs, the dogs may ingest the unhatched eggs.

These eggs hatch within the dog, where the larvae mature into adults, which then lay eggs to begin a new the life cycle

Tapeworms

Tapeworms are large worms that live in the gut of dogs. They may migrate about in the area around the dog's anus which can lead to irritating itching and thus bad hygiene by the dog. Tapeworms often have an intermediate host in addition to their final host (the dog). The most important intermediate hosts of canine tapeworms are fleas or certain mammals like sheep and rabbits.

The most common canine tapeworm is transmitted by fleas. Flea larvae become infected by ingesting tapeworm eggs that have been shed in the dog's feces. Dogs become infected if they swallow an infected flea while grooming. The tapeworms grow to maturity in the dog's gut. Tapeworm segments which contain eggs are then shed in the dog's feces. Tapeworms also can be transmitted when dogs eat the raw meat of infected intermediate hosts.

Adult tapeworms live in the guts of dogs, where they lay their eggs. The eggs are released with the dog's feces, where they then dwell.

As the larvae grow within the eggs, the eggs may be ingested by flea larvae that are also present in the dog feces. If a dog ingests an infected flea, the tapeworm larvae may hatch and mature in the gut of the dog.

The larvae mature within the gut of the dog where they may travel as far down as the anus. They generally lay their eggs in the gut

Heartworm Disease

Heartworm disease (dirofilariasis) is a serious and potentially fatal disease in dogs. It is caused by a worm called Dirofilaria immitis.

Heartworms are found in the heart and large adjacent vessels of infected dogs. The female worm is 6 to 14 inches (2.3 to 5.5 cm) long and 1/8 inch (5 mm) wide; the male is about half the size of the female. One dog may have as many as 300 worms.

> Adult heartworms live in the heart and pulmonary arteries of infected dogs. They have been found in other areas of the body, but this is unusual. They survive up to 5 years and, during this time, the female produces millions of young (microfilaria). These microfilaria live in the bloodstream, mainly in the small blood vessels. The immature heartworms cannot complete the entire life cycle in the dog; the mosquito is required for some stages of the heartworm life cycle. The microfilaria are therefore not infective (cannot grow to adulthood) in the dog, although they do cause problems.

As many as 30 species of mosquitoes can transmit heartworms. The female mosquito bites the infected dog and ingests the microfilariae during a blood meal. The microfilariae develop further for 10 to 30 days in the mosquito and then enter the mouth parts of the mosquito. The microfilariae are now called infective larvae because at this stage of development, they will grow to adulthood when they enter a dog. The mosquito bites the dog where the haircoat is thinnest. However, having long hair does not prevent a dog from getting heartworms.

When fully developed, the infective larvae enter the bloodstream and move to the heart and adjacent vessels, where they grow to maturity in 2 to 3 months and start reproducing, thereby completing the full life cycle.

Canine heartworm disease occurs all over the world. In the United States, it was once limited to the south and southeast regions. However, the disease is spreading and is now found in most regions of the United States and Canada, particularly where mosquitoes are prevalent.

The disease is not spread directly from dog to dog. An intermediate host, the mosquito, is required for transmission. Spread of the disease therefore coincides with the mosquito season. The number of dogs infected and the length of the mosquito season are directly correlated with the incidence of heartworm disease in any given area.

It takes a number of years before dogs show outward signs of infection. Consequently, the disease is diagnosed mostly in 4 to 8 year old dogs. The disease is seldom diagnosed in a dog under 1 year of age because the young worms (larvae) take up to 7 months to mature following establishment of infection in a dog.

Adult worms cause disease by clogging the heart and major blood vessels leading from the heart. They interfere with the valve action in the heart. By clogging the main blood vessels, the blood supply to other organs of the body is reduced, particularly the lungs, liver and kidneys, leading to malfunction of these organs.

Most dogs infected with heartworms do not show any signs of disease for as long as two years. Unfortunately, by the time signs are seen, the disease is well advanced. The signs of heartworm disease depend on the number of adult worms present, the location of the worms, the length of time the worms have been present, and the degree of damage to the heart, lungs, liver, and kidneys from the adult worms and the microfilariae.

The most obvious signs are:

a soft, dry, chronic cough
shortness of breath
weakness
nervousness
listlessness
loss of stamina
All of these signs are most noticeable following exercise, when some dogs may even faint.

Listening to the chest with a stethoscope will often reveal abnormal lung and heart sounds. In advanced cases, congestive heart failure may be apparent and the abdomen and legs will swell from fluid accumulation. There may also be evidence of weight loss, poor condition, and anemia.

Severely infected dogs may die suddenly during exercise or excitement.

Microfilariae(young worms) circulate throughout the body but remain primarily in the small blood vessels. Because they are as wide as the small vessels, they may block blood flow in these vessels. The body cells being supplied by these vessels are deprived of the nutrients and oxygen normally supplied by the blood. The lungs and liver are primarily affected.

Destruction of lung tissue leads to coughing. Cirrhosis of the liver causes jaundice, anemia, and general weakness because this organ is essential in maintaining a healthy animal. The kidneys may also be affected and allow poisons to accumulate in the body.

In most cases, diagnosis of heartworm disease can be made by a blood test that can be run in the veterinary hospital. Further diagnostic procedures are essential, in advanced cases particularly, to determine if the dog can tolerate heartworm treatment. Depending on the case, we will recommend some or all of the following procedures before treatment is started:

Serological test is performed on a blood sample. It is the most widely used test because it detects antigens (proteins) produced by adult heartworms. It will be positive even if the dog does not have any microfilaria in the blood; this occurs about 20% of the time. Dogs with less than five adult heartworms will not have enough antigen to turn the test positive, so there may be some false negative results in early infections. Because the antigen detected is produced only by the female worm, a pure population of male heartworms will give a false negative, also. Therefore, there must be at least 5 female worms present for the most common test to be positive.

Blood test for microfilariae is a blood sample is examined under the microscope for the presence of microfilariae. If microfilariae are seen, the test is positive. The number of microfilariae seen gives us a general indication of the severity of the infection. However, the microfilariae are seen in greater numbers in the summer months and in the evening, so these variations must be considered. Approximately 20% of dogs do not test positive even though they have heartworms because of an acquired immunity to this stage of the heartworm. Because of this, the antigen test is the preferred test. Also, there is another microfilarial parasite which is fairly common in dogs; on the blood smear, these can be hard to distinguish from heartworm microfilariae.

Complete blood counts and blood tests for kidney and liver function may give an indirect indication of the presence of heartworm disease. These tests are also performed on dogs diagnosed as heartworm-infected to determine the function of the dog's organs prior to treatment.

A radiograph of a dog with heartworms will usually show heart enlargement and swelling of the large artery leading to the lungs from the heart. These signs are considered presumptive evidence of heartworm disease. Radiographs may also reveal the condition of the heart, lungs, and vessels. This information allows us to predict an increased possibility of complications related to treatment.

An electrocardiogram (EKG) is a tracing of the electric currents generated by the heart. It is most useful to determine the presence of abnormal heart rhythms.

An echocardiogram allows us to see into the heart chambers and even visualize the heartworms themselves. Although somewhat expensive, this procedure can diagnose heartworms when other tests fail.

There is some risk involved in treating dogs with heartworms, although fatalities are rare. The drug that is used contains arsenic. The amount of arsenic is sufficient to kill heartworms without undue risk to the dog. However, dogs with poor liver or kidney function may have difficulty breaking down and eliminating the arsenic. In spite of this we able to treat more than 95% of dogs with heartworms successfully.

We see some dogs with advanced heartworm disease. This means that the heartworms have been present long enough to cause substantial damage to the heart, lungs, blood vessels, kidneys, and liver. A few of these cases will be so far advanced that it will be safer to just treat the organ damage rather than risk treatment to kill the worms. Dogs in this condition are not likely to live more than a few weeks or months.

An injectable drug to kill adult heartworms is given for two days. It kills the adult heartworms in the heart and adjacent vessels over a period of about 30 days.

Complete rest is essential after treatment. Some adult worms die in a few days and start to decompose; the remainder will die within a month. As they break up, they are carried to the lungs, where they lodge in the small blood vessels and are eventually reabsorbed by the body. This is a dangerous period, and it is absolutely essential that the dog be kept quiet and not be allowed to exercise for 1 month following treatment. The first week after the injections is very critical because the worms are dying. A cough is noticeable for 7 to 8 weeks after treatment in many heavily infected dogs.

Prompt treatment is essential if the dog has a significant reaction in the weeks following the initial treatment, although such reactions are not common. If a dog shows loss of appetite, shortness of breath, severe coughing, coughing up blood, fever, and/or depression, you should notify your vet. Response to antibiotics, cage rest, and supportive care, such as intravenous fluids, is usually good in these cases.

Treatment to kill microfilaria starts approximately one month following treatment to kill the adults, the dog is returned to the hospital for administration of a drug to kill microfilariae. Your dog needs to stay in the hospital for the day. Seven to ten days later a test is performed to determine if microfilariae are present. If they have been all killed, the treatment is complete. If there are still some present in the blood, treatment for microfilariae is repeated.

In some cases, the heartworm infection is "occult," meaning that no microfilariae were present. In this case, a follow-up treatment at one month is not needed.

In dogs with severe heartworm disease, it may be necessary to treat them with antibiotics, special diets, diuretics to remove fluid accumulations, and drugs to improve heart function prior to treatment for the heartworms.

Dogs with severe heart disease may need lifetime treatment for the failing heart, even after the heartworms have been killed. This includes the use of diuretics, heart drugs, aspirin, and special low salt, low protein diets.

Dog owners are usually pleasantly surprised at the change in their dog following treatment for heartworms, especially if the dog had been showing signs of heartworm disease. The dog has a renewed vigor and vitality, improved appetite, and weight gain.

When a dog has been successfully treated for heartworms, you cannot sit back and relax because dogs can be reinfected. Therefore, it is essential to begin a heartworm prevention program. There are three drugs which can be used to prevent heartworm infection. One is a daily, chewable tablet; the others are chewable tablets that are given only once monthly. All these products are very safe and very effective. Their costs are essentially identical. One of these should be started immediately after the treatment is completed.

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