Infectious Diseases in Dogs and Cats

by Bruce W. Little, DVM

Infectious Diseases in Dogs and Cats



Canine influenza, bird flu, swine influenza, Avian-type influenza that sickens cats, leptospirosis, parvovirus, Lyme Disease and on and on and on. The popular press is full of news about how viruses, bacteria and other microbes are infecting our family pets. It has been reported that the H3N2 Asian strain of the canine influenza virus has mutated so that it will now infect cats, and cats can transmit the virus to humans. In a recent article in the Journal of the American Veterinary Medical Association (AVMA), it was reported that 386 cats living in a New York City shelter facility came down with the illness. A veterinarian who was working with the cats contracted the disease as well; although it was reported the veterinarian suffered a mild form of the disease. What is a pet owner to do in the face of all these reports about the increase of these animal diseases, many of which can be transmitted to the human members of the family? A review of these viral and bacterial diseases should help to keep pet owners knowledgeable about how to prepare for these diseases.

A virus is a microscopic organism that can replicate only inside the cells of a host organism. They cannot live or carry on any life form outside a host. Viruses are so tiny they are observable only with a microscope. Viruses infect all types of organisms, including animals and plants, as well as bacteria and other microbes. Approximately 5,000 different viruses have been described in detail at the current time, although it is known there are millions of distinct types and mutations. Viruses are found in virtually every ecosystem on Earth, and these minute life forms are thought to be the most abundant type of biological entity. Viruses exhibit a combination of physical characteristics that has baffled scientists trying to categorize them for decades. They possess genes giving them a distinct genetic makeup and they are capable of reproduction while attached to their host body. However, viruses do not have a cellular structure and do not carry out their own metabolism as they require a host to sustain any living form. Viruses can attack a variety of cells in the animal body. Some viruses attack the blood, other viruses may attack the respiratory system or the liver or other body systems. Although we perceive viruses as causing disease, many viruses are beneficial to the animal body and the environment we live in. Contrary to popular belief, viruses are not killed using antibiotics. Although drugs are available that may slow down a virus’ progress, and we have drugs that may help relieve the symptoms of a viral infection, treatment of viral infections has remained an extreme challenge to scientists including veterinary scientists. Therefore, science and common sense tells us the best way to control the effects of viral diseases is to vaccinate against them if vaccine is available to do so. Effective vaccines have been manufactured that will protect dogs from several strains of canine influenza. Also, the vaccine might help to suppress the symptoms of other strains of influenza infection as well. It usually takes a series of vaccinations a few weeks apart to gain immunity in dogs for canine influenza with a follow-up vaccination about one year later. Talk to your veterinarian about vaccinating your dogs against canine influenza and booster vaccinations if needed. It may not be necessary for you to vaccinate if your geographic location has not seen cases of influenza. There are no vaccines approved for influenza in cats.

An extremely virulent virus, canine influenza is highly contagious and spreads rapidly from infected dogs to vulnerable dogs through direct contact, nasal secretions through coughing and sneezing, and contaminated objects such as food and water bowls, collars, leashes, kennel surfaces, chew toys and people moving between infected and uninfected dogs. Dogs are most contagious in the early stages of the disease after they become infected but are not yet showing signs of the disease. Symptoms of influenza begin with fever and may include lethargy, lack of appetite, coughing, nasal discharge and sometimes difficulty in breathing. If left unattended the disease can progress into more serious respiratory diseases including pneumonia. If you note any of these symptoms, keep your dog away from other dogs and call your veterinarian as soon as possible. Canine influenza can be diagnosed early in the illness by testing a nasal swab to see if the virus is present. The most accurate test is a blood test.

If a pet becomes sick, the chances are the causative agent is either a virus or bacteria. Bacteria are disease causing microbes found in all animals, and is equal to viruses in its distribution across all sectors of the Earth. Bacteria are found everywhere – on countertops, doorknobs, stair rails, bathrooms, even inside our bodies. Like viruses, all bacteria are not harmful, in fact, the entire digestion process of animals is dependent upon “good” bacteria to help in that process. Bacteria also serve as an immune system modulator that helps animals fight off disease. Bacteria are single-cell microorganisms that can reproduce outside of a host animal, and can thrive in many types of environments. The bacteria that can make our pets sick cause a wide range of symptoms and, left untreated, can kill them. Fortunately, antibiotics that have been developed by the pharmacy industry that can cure many diseases caused by bacteria. These drugs, which have revolutionized medicine in the 20th Century, have been a blessing for our pets. Together with vaccinations, antibiotics have wiped out many diseases in pets and humans since they came into use following World War II. The use of antibiotics has not been without controversy and abuse, however. Because many people think antibiotics are a miracle drug, people have requested them and some doctors have overutilized them to the extent that some bacteria have undergone mutations that resulted in a strain of bacteria that is rapidly becoming resistant to the effects of antibiotics, and they do not cure the animal of disease. The best example of this antibiotic resistance is the superbug, methicillin-resistant Staphylococcus aureus or MRSA. Use of antibiotics in livestock feed used as a disease preventive and growth stimulant has caused the bacteria to develop resistance to the antibiotic and they no longer are effective on animals that have contracted that disease. Many times, MRSA will become an opportunist bacteria and invade an animal when the animal’s resistance is depleted because of a compromised immune system. Those animals are very difficult to treat if they can be cured at all. Many end in death.

There is a long list of bacterial diseases that affect our pets. Among them are leptospirosis, a disease that may be transmitted through urine of rodents and other wild animals. The leptospirosis organism can live in water and in warm, wet soil. Leptospirosis is transmitted from animal to animal through direct contact with body fluids such as urine and blood, bite wounds, or indirectly through exposure to contaminated water or bedding. The disease can be transmitted if an animal licks an area where an infected animal has been. Wild animals can be a reservoir of chronic shedding of the bacteria by mice, rats, skunks, opossum, and raccoons. The disease can be transmitted from animals to humans. If your dog has not been vaccinated and is diagnosed with leptospirosis, be sure to take all sanitary precautions while cleaning up after the dog and cleaning your dog’s bedding. Wear disposable gloves when performing these chores. Leptospirosis causes flu-like symptoms, but it can develop into a more severe, life-threatening illness that causes dehydration and affects the kidneys, liver, lungs, and heart. Signs of leptospirosis include fever, muscle weakness, blood in the urine, loss of appetite, nausea, weight loss and death. Prevention includes vaccination and making common sense decisions about contact with wild animals, and day care and boarding facilities. Try to keep dogs from drinking from stagnant water puddles. And get them vaccinated for leptospirosis!

Another disease that is increasing in incidence across the United States at an alarming rate is parvovirus. Parvovirus is extremely virulent and will infect all dogs that have not been vaccinated or have had prior exposure to the virus thereby accumulating some immunity. The vaccine is effective if properly administered and will protect your dog from getting this terrible disease. Parvovirus is a highly contagious disease that is spread by direct contact with an infected dog or wild canine species, or indirectly by the fecal-oral route. Symptoms of parvovirus infection include vomiting, diarrhea, elevated temperature, and general weakness leading to dehydration, and if not corrected, can lead to death. Treatment usually includes supportive therapy to offset the dehydration and weakness. Also, antibiotics may be needed to control secondary bacterial infections. It may take several weeks of concentrated treatment to cure a dog of parvovirus infection, and a large percentage die from the effects of the disease. So, the cost to treat parvovirus infection can be substantial. It is much cheaper to provide your dog with vaccine than to treat it for this disease.

Are vaccinations for viral and bacterial diseases in dogs and cats harmful to your pet? They can be because they are biological and they can cause side effects just like they can in people. However, in almost all cases, the benefits of vaccinating far, far outweigh the risks of giving the vaccine. And the cost is much, much cheaper! Aside from protecting the health of your own pet, vaccinating our pets serves a greater cause than simply providing the care and well-being for our own pet. As a percentage of the population of animals in any given area are immunized with vaccines or through natural immunity, the resistance to the effects of the virus or bacteria are multiplied. Epidemiologists have determined that if 70 to 78 percent of animals in a regional population are vaccinated or have gained natural immunity through exposure, the diseases are primarily contained and controlled. In the veterinary profession, we call this herd protection. If we do our job as responsible pet owners, we not only provide maximum care for our own pets, but we help provide prevention of the disease in total. That is why the municipality laws regarding rabies have become so effective in controlling rabies in developed countries such as the United States. In third-world countries rabies is rampant with approximately 70,000 people worldwide dying from rabies each year according to the Centers for Disease Control and Prevention (CDC). Greater than 99% of those deaths occur in Africa and Asia with almost one-third of the deaths in India alone. Some sixty percent of deaths due to rabies are children under age 15 who were bitten by a dog. It is rare for a human being to die from rabies in the United States of America, although in any certain year one or two deaths can occur. This huge disparity between developed countries and poor, third-world countries is primarily due to laws and regulations by municipal governments that regulate dog and cat owners to vaccinate their pets with highly effective rabies vaccines. Rabies, once it reaches the central nervous system in the body and exhibits clinical signs, is 99.9% fatal, but it is also 100% preventable. Eliminating the disease by vaccinating dogs and cats protects the pets and stops transmission to people. Talk to your veterinarian about a vaccination program for all your pets. There is a core vaccination strategy that all pet owners, in conjunction with and upon the advice of your veterinarian, will serve both dogs and cats well, and it will be much cheaper than treating them once they develop the signs of any viral or bacterial disease. You and your pets will be glad you did.



Bruce W. Little, DVM