Rabies is a severe, and often fatal, viral polioencephalitis that specifically affects the gray matter of the dog’s brain and its central nervous system (CNS). The primary way the rabies virus is transmitted to dogs in the United States is through a bite from a disease carrier: foxes, raccoons, skunks, and bats. Infectious virus particles are retained in a rabid animal’s salivary glands to better disseminate the virus through their saliva. Once the virus enters the dog’s body, it replicates in the cells of the muscles, and then spreads to the closest nerve fibers, including all peripheral, sensory and motor nerves, traveling from there to the CNS via fluid within the nerves. The virus can take up to a month to develop, but once the symptoms have begun, the virus progresses rapidly.

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This inflammatory infection also has zoonotic characteristics and can therefore be transmitted to humans. Rabies is one of the most known deadly diseases, and vaccinations are generally required by law.

Canine distemper is a contagious and serious viral illness with no known cure. The disease affects dogs, and certain species of wildlife such as raccoons, ferrets, wolves, foxes, and skunks. Canine distemper is a relative of the measles virus, which affects humans, the Rinderpest virus that affects cattle, and the Phocine virus that causes seal distemper. Young, unvaccinated puppies and non-immunized older dogs tend to be more susceptible to the disease.

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The virus, which is spread through the air and by direct or indirect (i.e. utensils, bedding) contact with an infected animal, initially attacks a dog’s tonsils and lymph nodes and replicates itself there for about one week. It then attacks the respiratory, urogenital, gastrointestinal, and nervous systems. Normal healthy dogs can begin having a fever and become lethargic quickly. Latter symptoms include vomiting, the inability to stand/walk, seizures, and death within two to five weeks after the initial infection.

The canine parvovirus (CPV) infection is a highly contagious viral illness that affects dogs. The virus manifests itself in two different forms. The more common form is the intestinal form, which is characterized by vomiting, diarrhea, weight loss, and lack of appetite (anorexia). The less common form is the cardiac form, which attacks the heart muscles of very young puppies, often leading to death.

Death can occur within days if not treated. The majority of cases are seen in puppies that are between six weeks and six months old. The incidence of canine parvovirus infections has been reduced radically by early vaccination in young puppies.

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While sometimes treatable if caught early, the cost of treatment ranges from $750+ per dog. Even after a dog has recovered from a CPV infection, it will still have a weakened immune system, and will be susceptible to other illnesses.

Kennel cough, the common name that is given to infectious canine tracheobronchitis and medically known as bordetella, is a very highly contagious respiratory disease among dogs. As the name of the disease suggests, it is typified by inflammation of the trachea and bronchi. Young puppies can suffer the most severe complications that can result from this disease, since they have an underdeveloped immune system that is still strengthening. Also at increased risk are older dogs, which have decreased immune capabilities, and pregnant bitches, which also have lowered immunity to infections.

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Since it is so infectious, many boarding facilities, daycares, and grooming salons require the bordetella vaccination. Symptoms include a dry hack or cough, retching and watery nasal discharge. If symptoms progress, they can include pneumonia, inappetence, fever, lethargy and even death.

Leptospirosis is an infection of bacterial spirochetes, which penetrate the skin and spread through the body by way of the bloodstream. Leptospires spread throughout the entire body, reproducing in the liver, kidneys, central nervous system, eyes, and reproductive system. Soon after initial infection, fever and bacterial infection of the blood develop, but these symptoms soon resolve with the reactive increase of antibodies, which clear the spirochetes from most of the system. The extent to which this bacteria affects the organs will depend on a dog’s immune system and its ability to eradicate the infection fully.

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Even then, Leptospira spirochetes can remain in the kidneys, reproducing there and infecting the urine. Infection of the liver or kidneys can be fatal for animals if the infection progresses, causing severe damage to these organs. Younger animals with less developed immune systems are at the highest risk for severe complications. Other symptoms include depression, shivering, loss of appetite, weakening of the muscles, swelling of the lymph nodes, and bloody discharge.

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The Leptospira spirochete bacteria is zoonotic, meaning that it can be transmitted to humans and other animals. Children are most at risk of acquiring the bacteria from an infected pet.

Dogs can only get heartworms by the bite of an infected mosquito. But, there’s no way to tell if a mosquito is infected. Heartworm disease has been reported in all 50 states. And the bite of just one mosquito infected with the heartworm larvae will give your dog heartworm disease. It takes about seven months, once a dog is bitten by an infected mosquito, for the larvae to mature into adult heartworms. They then lodge in the heart, lungs, and surrounding blood vessels and begin reproducing. Adult worms can grow up to 12 inches in length, can live 5-7 years, and a dog can have as many as 250 worms in its system.

Infectious canine hepatitis is a viral disease that is caused by the canine adenovirus CAV-1, a type of DNA virus that causes upper respiratory tract infections. This virus targets the functional parts of the organs, notably the liver, kidneys, eyes, and endothelial cells (the cells that line the interior surface of the blood vessels).

The virus begins by localizing in the tonsils around 4 to 8 days after nose and mouth exposure. It then spreads into the bloodstream and localizes in the Kupffer cells (specialized white blood cells located in the liver) and endothelium of the liver. During this stage of the infection, the virus is shed into the feces and saliva, making both infectious to other dogs. In a healthy dog with an adequate antibody response, the viral cells will clear the organs in 10 to 14 days but will remain localized in the kidneys, where the virus will continue to be shed in the urine for 6 to 9 months.

In dogs with only partial neutralizing antibody response, chronic hepatitis takes place. This severe condition often results in cytotoxic ocular injury due to inflammation and death of the cells in the eye with inflammation of the front of the eye (anterior uveitis). This condition leads to one of the more outwardly visible and classic signs of infectious hepatitis: “hepatitis blue eye.”

*Information on this page was gathered from petMD.