Dogs get sick.

Dogs get sick from parasites, viruses, bacteria, protozoa, and fungus.

In some cases, these diseases and infestations are fatal unless caught early and treated. Sometimes they sow the seeds of death or debilitation years down the road by causing chronic illness or damaging organs.

Fortunately, veterinary researchers have developed drugs and treatments that reduce the occurrence and effects of many diseases and parasites, but they do not eradicate the scoundrels - they only hold them at bay.

Rabies, distemper, parvovirus, hepatitis, parainfluenza, and coronavirus are major viral diseases affecting dogs. Lyme disease, leptospirosis, and a type of kennel cough are bacterial diseases. These infections are not limited to dogs - all are found in other animal populations and rabies, Lyme, and lepto also infect people. Each of these diseases can be prevented by judicious vaccination of puppies and adult dogs.

Vaccinations work by priming the pump, that is, they stimulate the dog's immune system to produce specific antibodies to fight a subsequent attack by the disease. Vaccines come in two forms: modified live formulas that include a weakened form of the disease and killed or inactivated formulas that have an additional substance called an adjuvant added to boost the immune response. Each has its advantages. Modified live vaccines can cause swift development of long-lasting immunity but may produce mild cases of illness. Killed vaccines are more stable, have a longer shelf life, and do not produce mild infections, but the protection may not last as long.

If the mother dog is vaccinated, her puppies will get some immunity from colostrum, her first milk. Because it is difficult to determine when that immunity wears off and vaccinated immunity kicks in, puppies generally get a series of shots. After the initial puppy shots, veterinarians recommend a booster at one year of age and subsequent boosters every six months, year, or three years, depending on the disease and its prevalence in an area.

Vaccines can be given separately or in combination.

Some dogs have had reactions to vaccinations, and some dog breeders, owners, and veterinarians question whether puppy immune systems can be overloaded with too many vaccines administered too close together or whether annual boosters are necessary for many dogs. Researchers trying to answer these questions have determined that some dogs are protected for more than a year by some vaccines, and some veterinarians recommend three-year intervals for older dogs that aren't exposed to other animals that may carry the diseases. However, the work is in its infancy and, while some veterinarians and universities have modified their vaccination recommendations as a result, none have backed away from vaccines as the first line of defense to these debilitating or deadly diseases.

The rabies virus is fatal once symptoms appear. Rabies vaccination is required by law at local or state levels because the disease is fatal to humans as well as dogs, raccoons, coyotes, foxes, skunks, cats, and other mammals.

Some veterinarians use three-year rabies vaccine; those in areas with disease outbreaks give boosters every year for maximum protection.

The American Veterinary Medical Association considers canine distemper to be the greatest single disease threat to the world's dog population.

Canine distemper virus is fatal to 80 percent of the puppies and 50 percent of the adult dogs that contract it. Symptoms include congested lungs, nasal discharge, gunky eyes, coughing, weight loss, vomiting, and diarrhea. As the disease progresses, it attacks the nervous system, often causing partial or complete paralysis and seizures.

Distemper is highly contagious. Dogs can get the virus through the air, by direct contact with urine, feces, or secretions from infected dogs, and by contact with kennels, bedding, toys, or other objects that may hold the virus.

According to AVMA, "Some veterinary medical scientists estimate that practically every dog that lives to be a year old has had contact with the virus at some time. ... Distemper is so prevalent and the signs so varied that any sick young dog should be taken to a veterinarian for a definite diagnosis."

Most distemper cases appear in dogs less than six months of age and in old dogs that have not been routinely vaccinated. Once the dog is infected, there is no cure. Treatment is supportive; i.e., fluids are given to prevent dehydration and symptoms are treated, but the disease must run its course. Dogs that recover from distemper may develop hardened foot pads and nose leathers and have vision and nervous system problems throughout their lives. In addition to these consequences, puppies may also have mottled teeth from damage to developing enamel.

Distemper can be prevented by vaccination. Some university studies indicate that immunity lasts longer than a year after inoculation, but pet owners should discuss frequency of vaccination with their veterinarian. Generally, older dogs that remain at home may not need annual boosters, but dogs that spend time in training classes, grooming shops, day care centers, or boarding kennels; dogs that participate in public events; and dogs that compete at shows and trials should be vaccinated.

The North Carolina State University published a vaccination protocol in 2001 that "highly recommended" vaccination against distemper with a modified live vaccine but noted that, because some studies indicate that dogs are still protected for five years or more when challenged by the disease, "a booster vaccination of every three years among adult dogs is reasonable."

Distemper develops over a course of days, but parvovirus can overwhelm a dog within hours of the first symptoms and result in death within 48-72 hours.

Found throughout the world, parvo is a highly contagious disease that attacks the intestinal tract, the white blood cells, and sometimes the heart. It is spread through contact with the feces of infected dogs and can be carried on shoes, crates, equipment, or on the hair or feet of infected dogs. One infected dog at a show, a canine expo, a charity walk, a shelter, a boarding kennel, or any other event or facility where dogs congregate can spread the virus to hundreds of unprotected dogs.

Symptoms of parvo appear five-to-seven days after exposure and include depression, loss of appetite, vomiting, and severe diarrhea. Feces are generally light gray or yellow-gray and may be streaked with blood. Puppies under the age of six months are most susceptible to the disease. If the virus attacks the heart, puppies can die within hours or live for a few weeks or months. Rottweilers and Doberman Pinschers appear to be at higher risk for parvo than other breeds.

As with distemper, there is no treatment that kills the virus. Instead, nursing care consists of replacing fluids lost in diarrhea and vomiting, keeping the dog warm, controlling vomiting and diarrhea, and dosing with antibiotics to prevent secondary infection.

Because parvovirus can live for months in an infected area, thorough cleaning of all surfaces is necessary to eradicate the disease in a kennel or home. Household bleach is an effective cleansing agent.

Vaccination against parvo has dramatically reduced incidence of the disease. The NCSU protocol "highly recommended" vaccination with a modified live virus vaccine and noted that dogs are still protected against parvo when challenged by the disease as much as seven years later.

Hepatitis is also known as canine adenovirus type 1 or CAV-1. It is inhaled or ingested by the dog, enters the bloodstream, and targets the liver, kidneys, eyes, and the cells lining the inner surface of the blood vessels. Some cases barely show symptoms; puppies may have a slight fever or be slightly lethargic and recover quickly. Some cases are quick and deadly; puppies show fever, tonsilitis, reddened mouth and eye membranes, colic, then shock and death, sometimes within 24 hours.

The in-between manifestation of the disease is the one most commonly described. The early symptoms are similar to the other forms; some puppies recover within a week, but others develop internal bleeding, central nervous system involvement, and liver disease.

There is no cure, only supportive treatment. Vaccination against this disease is actually done with a modified live or killed product made from CAV-2, the other adenovirus that affects dogs. The NCSU protocol recommended vaccination with CAV-2 but noted that dogs challenged with the disease as much as seven years after vaccination were still protected.

This common name for respiratory disease in dogs covers the actions of several infectious agents, including Bordatella bronchiseptica, a bacteria, canine adenovirus-2, and canine parainfluenza virus.

The parainfluenza virus is related to the canine distemper virus. Symptoms of these diseases range from a dry hacking cough to inflammation of the larynx, bronchial tubes, and trachea. CAV-2 also produces pneumonia in 10-20 percent of the affected dogs.

Kennel cough agents are highly contagious, especially in kennels or shelters where canine immune systems are stressed, leaving dogs susceptible to pre-existing infections or new attacks from infected dogs. Good kennel ventilation helps prevent these infections from taking hold, but vaccination is the only sure preventive.

A combined kennel cough vaccination contains CAV-2, parainfluenza, and Bordatella in one dose of nose drops. While the diseases usually present symptoms no more severe than a bad cold, vaccination is recommended if dogs are to be boarded or will come in contact with large numbers of dogs.

Leptospirosis is a bacterial disease spread in the urine of wild and domestic animals and capable of causing illness in humans as well as dogs. Several species of the bacteria produce disease in dogs. Symptoms include lethargy, kidney inflammation, low-grade fever, vomiting, reddening of the mucous membranes and conjunctiva, and blood clotting abnormalities. A more generalized form of the disease can cause elevated liver enzymes, jaundice, pneumonia, and intestinal inflammation. Chronic kidney problems can result.

Antibiotic therapy is effective in fighting the bacterial invasion and supportive nursing (replenishment of fluids, administration of diuretics to flush the kidneys and prevent kidney failure, blood transfusions if necessary) is required.

Lepto vaccines, however, are not recommended unless there is a disease problem in the area. The vaccines help lessen the severity of the disease but do not prevent it and may not be effective for more than six months. Furthermore, puppies and small dogs can have adverse reactions to the vaccines. Therefore, many veterinarians do not recommend inoculation against leptospirosis. However, if a lepto outbreak occurs and veterinarians do recommend vaccination, dogs should be inoculated against all four strains of the disease unless the particular strain is identified.

Lyme is a bacterial disease spread by ticks. Symptoms in dogs include lethargy, joint pain, lack of appetite, lymph node enlargement, and fever. Some dogs have antibodies to the disease, indicating that they have been exposed, but they show no symptoms.

Treatment is with the antibiotic tetracycline.

A vaccine is available but is not widely recommended because the disease is self-limiting and protection is limited to no more than six months following inoculation.

Lyme disease is more serious for humans than for dogs. Thus it is important to eliminate ticks by removing them from the dog and using appropriate chemical and biological controls.

This virus causes diarrhea and vomiting and can be confused with parvovirus. The mode of infection is direct contact with an infected animal or its feces. Some dogs have antibodies but no symptoms; others lose their appetite, have smelly diarrhea, and are lethargic and dehydrated.

Treatment involves replacing lost fluids and controlling vomiting and diarrhea. A vaccine is available but not widely recommended. The NCSU guidelines noted that the disease is not widespread enough to justify routine vaccination of all dogs.

There are no proven vaccine substitutes. Some dog owners who use alternatives to modern medicine use nosodes, but there is no evidence that these concoctions can successfully prevent disease. There is some evidence, however, that they can help dogs recover from the disease when they get sick.

Some owners fear that their dogs will experience adverse reactions to vaccines, but these reactions are rare. Those who worry about overloading a dog's immune system with multivalent (multiple vaccines in a single shot) inoculations can ask their veterinarian to purchase monovalent (single) vaccines for distemper and parvo and give the shots at different times.

Some dog owners have their dogs tested to determine a level of immunity and make vaccination decisions based on the results. The test is done by drawing blood and checking it for titers, a measurement of the antibodies present in blood serum. A titer must be run for each disease, and the tests are far more expensive than the vaccination. Titers quantify the dog's reaction to the vaccination but do not necessarily indicate that the dog would be protected against an active case of disease.