Viral Diseases of Dogs

Viral Diseases of Dogs

Common and important viral diseases of dogs are rabies, canine distemper, kennel cough, parvoviral gastroenteritis, etc.

Important Viral Diseases of Dogs
Important Viral Diseases of Dogs

Rabies in Dogs

For most people, hearing the word rabies strikes great fear. With Hollywood portrayals such as “Cujo,” and often lethal result of a rabies infection, these fears are somewhat justified. But with understanding and knowledge, fears can be replaced with a healthy respect for the virus.

The rabies virus can infect almost any mammal. It is shed in the saliva and transmitted typically by bite wounds.

Without treatment, the virus eventually attacks the nervous system and results in death.

Throughout the world, 35,000 people die each year from rabies. In the United States, about 3 people succumb each year to rabies.

Rabies is most commonly found in skunks, raccoons, foxes, coyotes and bats. Despite their bad rap, rabies in ferrets is quite uncommon. Since 1958, only 22 ferrets have been diagnosed with rabies.

Recently cats have become the number one domestic animal diagnosed with rabies. It is suspected this is due to more cats being kept as pets and allowed to roam their neighbour-hoods.

Diagnosis

Diagnosing rabies can be difficult. In the early stages, the virus has not yet attacked the brain and the animal acts normally.

There are no body changes and no test that can determine if an animal or person was exposed to the virus.

Unfortunately, the only way to diagnose rabies is to examine brain tissue, and this can only be done after the animal is dead.

Treatment

Treatment is not recommended for rabies in dogs. Euthanasia is required.

Rabies is a fatal virus and there is no treatment for those animals in the final stages of the disease.

People exposed to rabies can receive injections to reduce the risk of rabies infection but these injections have not been extensively tested in animals.

Due to the serious risk of transmission to humans, animals that have been bitten by another animal with confirmed rabies should be euthanized.

Canine Distemper in Dogs

Canine distemper is a highly contagious disease caused by canine distemper virus (CDV). It may affect the respiratory, gastrointestinal and neurologic systems in the body.

It is generally transmitted through contact with mucous and watery secretions discharged from the eyes and noses of infected dogs.

However, it can also be transmitted by contact with urine and other bodily fluids of infected dogs, so dog may become infected without coming into contact with an infected dog.

Air currents and inanimate objects can also carry the virus.

Distemper was a common infection in dogs many years ago, but the incidence has been significantly decreased through widespread vaccination of dogs.

Canine distemper is now most commonly seen in young, unvaccinated or immune-compromised dogs. More than 50 percent of dogs that contract the disease die from it.

Even if a dog doesn’t die, canine distemper can cause irreparable damage to the nervous system, leaving the dog with partial or total paralysis or seizures.

Canine distemper can strike any dog of any breed or any sex, although it is most common in young dogs.

Diagnosis

Diagnosis is often difficult, since there is no one reliable test for the disease. Diagnosis is usually suspected from the history and clinical signs.

Recommend the following tests:

  • A complete blood count (CBC), biochemical profile, and urinalysis.
  • X-rays of the chest and abdomen.
  • Cerebrospinal fluid (CSF) testing if neurologic signs are present.
  • Examination of buffy coat smears (the layer of white blood cells formed when blood is spun down) and/or conjunctival scrapings from under the eyelid for distemper viral particles).
  • Measurement of distemper antibody titers in blood or the cerebrospinal fluid.

Differential Diagnosis

The respiratory form of canine distemper must be differentiated from the following:

  • Kennel cough, or infectious tracheobronchitis, is a contagious respiratory disease of dogs that is manifested by coughing.
  • This is a transient disease, and most dogs recover without severe complications.
  • Pneumonia due to other infections (bacterial, fungal) can present similarly to dogs with distemper.

The gastrointestinal (GI) form of canine distemper must be differentiated from the following:

  • Other GI viral diseases including parvovirus and coronavirus.
  • Bacterial enteritis including Campylobacter, Salmonella and Clostridia.
  • Protozoal infections, specifically, Giardia.
  • Ingestion of foreign bodies and toxins.
  • Any non-infectious disorder that causes vomiting and diarrhea in dogs.

The central nervous system (CNS) form of canine distemper must be differentiated from the following:

  • Granulomatous meningoencephalitis is a progressive, inflammatory disease of the central nervous system of dogs.
  • Many signs seen in this disorder may mimic the neurologic form of canine distemper.
  • Protozoal encephalitis is an inflammation of the brain, caused by one of the protozoal organisms (neosporosis, toxoplasmosis).
  • Cryptococcosis is a systemic fungal infection that affects particularly the respiratory and neurologic systems.
  • Lead poisoning commonly produces clinical signs that involve both the gastrointestinal tract and nervous system.

Treatment

Dogs with distemper may need to be hospitalized and must always be kept in isolation to prevent infection of other dogs.

Therapy is mainly supportive and symptomatic, as there are no antiviral drugs that are effective against distemper.

Because there are several clinical manifestations of distemper, there is no single treatment plan that can be recommended for all dogs.

The pet owner whose dog has distemper should also understand that even with the best of care, up to 50 percent of dogs infected with canine distemper succumb to the disease.

Intravenous fluid and electrolyte therapy may be recommended in the patient who has severe gastrointestinal signs, is unable or unwilling to eat, and is dehydrated.

Parenteral (intravenous) nutrition may be indicated in the debilitated patient, especially when protracted vomiting and diarrhea are present.

Administration of antiemetic drugs to stop vomiting may be of benefit. Antibiotics are indicated to control secondary bacterial infections.

Many dogs with severe distemper infections are immunocompromised, which means their immune system is functioning less than optimally, and they are susceptible to other infections.

In dogs that develop seizures, anticonvulsant therapy may be administered.

There is no effective treatment available for the myoclonus or tics that are produced in some dogs by distemper.

ITB (Infectious Tracheobronchitis) in Dogs

The cough associated with acute infectious tracheobronchitis, (ITB) or kennel cough, is a high-pitched, honk-like cough, sometimes followed by retching.

Kennel cough is a highly contagious inflammation of the trachea (windpipe) and bronchial tree caused by a contagious virus (adenovirus, parainfluenza virus, canine distemper virus) or bacterium (Bordetella bronchiseptica).

The disease is associated most often with dogs housed in a high-density population or boarding kennel.

The infectious agents can be transmitted through the air or by contact with contaminated surfaces.

Puppies and younger dogs are at greatest risk, but even old dogs can acquire kennel cough.

The incubation period from the time the dog first contracts the infection to the time that symptoms develop is typically between 3 to 10 days, and the symptoms can last for days to weeks.

A mild to moderate cough without other symptoms is usually self-limiting; however, occasional cases become lingering and cause chronic bronchitis.

Diagnosis

Complete medical history will usually reveal recent exposure to a kennel or other dogs. Windpipe sensitivity is present in most cases.

Diagnostic tests are needed to recognize kennel cough and exclude other diseases.

These tests may include:

  • A chest X-ray may be recommended to determine if pneumonia is present.
  • Routine laboratory blood tests-a complete blood count (CBC) or blood chemistry panel is not necessary unless dog is showing signs of generalized illness, fever or loss of appetite.
  • A fecal flotation should be done to exclude intestinal parasites.
  • If signs of eye involvement are observed, the cornea of the eye should be examined carefully.

Treatment

Therapy is controversial because the disease is usually self-limiting (like a human cold) and, if a viral infection is suspected, antibiotics can’t kill the virus.

This is especially true in mild, uncomplicated cases where treatment is supportive-not unlike that given to a person with a bad cold.

Treatments for kennel cough may include one or more of the following:

  • Cough suppressants are appropriate for some pets with kennel cough.
  • Injections or pills (butorphanol) are often used, but occasionally, a stronger medicine is needed (codeine-related) to break the cough cycle.
  • Antibiotics are used in some patients, especially if Bordetella infection or secondary bacterial infection is likely.

If the symptoms do not improve or should they become chronic, a careful re-evaluation including blood tests and a chest X-ray is indicated.

Parvo Viral Gastroenteritis in Dogs

Parvovirus (Parvoviral Enteritis or “Parvo,” for short) is a virus causing severe infection in puppies and dogs.

It invades and destroys rapidly growing cells in the intestine, bone marrow and lymphoid tissue resulting in nausea, vomiting and severe hemorrhagic (bloody) diarrhea.

The invasion of the bone marrow cells causes a decrease in the white blood cell count leading to increased susceptibility to bacterial infections and sometimes to a shock-like condition called endotoxemia. The disease can vary from mild to fatal if not properly treated.

Parvovirus is extremely contagious to other dogs. Infection is generally attributed to ingestion of material contaminated by dog feces and can occur when a dog smells or licks the ground.

Direct contact with another dog is not necessary for infection. Parvovirus is shed in the feces of infected dogs for approximately two weeks after initial ingestion and can live in the environment for years. The virus is species specific and is not contagious to cat or humans.

Dogs at highest risk for infection are unvaccinated puppies or those who have not yet completed their vaccine series.

It is most common in dogs less than 8 months old. Especially susceptible breeds include Doberman pinschers, Rottweilers, German shepherd, Staffordshire terriers, black Labrador retrievers, and dachshunds. Dogs of all ages can be infected, but puppies and younger dogs are most susceptible. Intact male dogs may also be susceptible for unknown reasons.

Unsanitary and/or overcrowded kennels may increase chance of infection and concurrent infection with parasites, other bacteria or viruses may also increase susceptibility to infection.

Proper vaccination of dog can best prevent the disease.

Parvovirus is an acute and serious disease, not a chronic condition. Virtually all cases need proper diagnosis and hospitalization.

Diagnosis

  • Diagnosis is usually based on clinical signs.
  • Diagnostic tests are needed to recognize parvovirus, and exclude other diseases. Tests may include:
  • Complete medical history and physical examination.
  • Testing the feces for the presence of the virus.
  • Blood tests and abdominal X-rays to determine the severity of the infection or exclude other causes of the symptoms.

Treatment

  • Recommend hospitalization.
  • Therapy is dependent upon the severity of the clinical symptoms and is aimed at treating the dehydration, controlling vomiting and diarrhea and preventing secondary infection.
  • If bacterial infection and dehydration can be prevented, clinical signs will usually resolve in 2 to 5 days. Therapy may include:
    • Intravenous (IV) fluid therapy, antibiotics and/or other drugs used to replace electrolyte and fluid losses and control nausea and vomiting.
    • In very severe cases, referral to a 24-hour critical care center may be recommended.

Preventative Care

  • Prevention is possible by vaccinating pet regularly to help prevent infection.
  • Keep dog away from fecal waste of other dogs when walking along neighbour hood streets or parks.
  • If dog leaves his own “deposit” be sure to remove it and dispose of it at home.
  • Minimize contact of unvaccinated puppies with other dogs that may be sick or unvaccinated.
  • This should include avoiding areas where other sick pets may have been (parvo can live in the environment for 2 years).
  • Dog is most at risk until fully vaccinated (usually 20 to 24 weeks of age).

Prognosis

  • Approximately 80 to 90 percent of affected dogs will survive and lead normal lives if disease is detected early and proper treatment and hospitalization is sought and administered.
  • Prognosis is worse for high-risk breeds.
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