- Keeping your dog safe from viruses, bacteria, and parasites
- Protecting yourself and your family from the bugs that like your dog
Scientists know of millions of species of viruses, bacteria, fungi, and parasites — and they discover new ones every day. Although this chapter discusses bugs that are problematic to dogs, most microorganisms don’t cause disease. They live in the soil and infect plants, animals, and even humans, but you can’t even tell they’re there unless you look.
In fact, microscopic critters are an important part of the circle of life. Without bacteria and fungi to decompose organic matter, humans would long ago have been buried in debris. Without the bacteria that digest plant material in the stomachs of cows, you’d have no milk or beef. Without the bacteria that inhabit your body, you would soon die of infection. Yes, ironically, beneficial bacteria even protect you from infection by their nasty relatives.
The bugs discussed in this chapter are the rare ones that infect dogs and cause systemic diseases (ones that affect the entire body).
Vaccinating against Viruses
Viruses are the smallest bugs scientists know of. You can fit 25 million viruses on the period at the end of this sentence. Viruses must grow inside a host cell; they can’t replicate on their own. Although this fact may seem like it would be a disadvantage to a virus, it’s exactly what makes viral infections so hard to fight. After all, how do you kill a virus that’s living in a cell without killing the cell itself? Because of this problem, very few drugs effectively treat viral infections, and many of the existing antiviral drugs are quite toxic.
The key to fighting a viral infection, therefore, is to make sure that your dog never gets infected, and the best way to accomplish this is to vaccinate him. Most of the vaccines given to dogs are designed to prevent viral infections: rabies, distemper, parvovirus, parainfluenza, and adenovirus (and kennel cough, though that can also be caused by bacteria). The following sections provide a little bit of information about the worst of the bad bugs. When you know what they can do to your furry friend, you’ll never want to get behind on his vaccinations. As always, talk to your vet about which vaccinations your dog may benefit from.
This viral infection is the most important infectious agent that you should vaccinate your dog against. Rabies vaccinations are so important, in fact, that in North America, it is illegal to have a dog who is not vaccinated for rabies. In most states, a dog who has bitten a person and is not vaccinated for rabies can be impounded and perhaps destroyed. Why does the government care whether your dog gets rabies? It’s simple: Rabies can be transmitted to humans by the saliva of an infected dog, through either a bite wound or a cut. When a person becomes ill with rabies, it is generally fatal if not treated within two weeks of the injury.
If you want to see the incredible (and justified) fear people had of rabid dogs in the days before the rabies vaccine was developed, watch the film To Kill a Mockingbird. In that movie, a rabid dog stumbles down a residential street while people hide in their homes, watching it and hoping that someone will have the courage to confront the dog and shoot it.
Rabies usually infects an animal (or human) through a wound such as a bite. When the virus enters the body, it moves to a nerve and then travels up the nerve to the spinal cord and brain, where the virus replicates and kills brain cells. The victim then begins to act in bizarre ways: Dogs may become very hyperactive and aggressive, or they may become weak and unresponsive. Death occurs in days, weeks, or months, depending on how far the virus has to travel through an animal to get to the central nervous system.
Luckily, vaccination of dogs against rabies is virtually 100 percent effective, and humans can share home and hearth with their canine companions without concern. Rarely anyone in a developed country contracts rabies today. However, in less developed countries, such as India, 50,000 people (mainly children) still die every year from rabies.
Puppies should be vaccinated against rabies for the first time after 12 weeks of age and then again at 1 year of age. After that, they should be vaccinated yearly or every three years, depending on state laws and the type of vaccine used. When your dog is vaccinated, you receive a vaccination certificate and a rabies tag. Always make sure that your dog wears her rabies tag, and keep the rabies vaccination certificate in a safe place where you can easily find it. If your dog escapes and bites someone, her rabies tag (and your vaccination certificate) will provide proof to animal control officers, veterinarians, and physicians that the dog was vaccinated. This documentation will prevent the unfortunate person from having to undergo post-exposure prophylaxis, a series of rabies shots designed to stop the virus in its path through the body to the brain.
Many species of wild animals throughout North America can live normal lives while being infected with rabies. The most common species are foxes, raccoons, skunks, and bats, but other animals can be infected, too. In many species, including skunks and raccoons, the virus can be present at high levels in the saliva and blood without even causing the animal to become ill. For this reason, it is never a good idea to keep these wild animals as pets; in some states and provinces, doing so is illegal. The risk of exposing humans to rabies is just too high.
Never touch a dog, cat, or any wild animal who is staggering, acting aggressively, or otherwise behaving bizarrely. If such an animal bites you — or if any animal you don’t know bites you — get medical attention immediately. Never touch a wild animal that approaches you. Wild animals should have a natural fear of humans. If they don’t, it may be because they are suffering from rabies.
Canine parvovirus enteritis was first identified in the late 1970s, when it swept through dog populations worldwide, killing thousands. The veterinary community worked tirelessly to determine the most effective ways to treat the condition, identify the virus, and produce a vaccine. An effective vaccine was developed and put into use within three years, quickly reducing the number of deaths.
Parvovirus attacks and kills the cells that line the small intestine. As a result, the dog cannot absorb the fluids in the intestine and the dog develops diarrhea, often with blood. Dogs with parvovirus often vomit because of the upset in their digestion. Some people say that they can smell a particular odor in parvovirus-infected puppies. Mildly affected dogs may recover in a few days, but severely affected dogs become depressed and dehydrated, and can die within a day or two. The severity of the parvovirus infection depends on the dog’s immunity to the virus. Dogs with inadequate immunity, especially puppies, still continue to die of parvovirus enteritis despite treatment. If your dog has diarrhea for more than 24 hours or has diarrhea with blood in the stool, seek veterinary attention.
Unfortunately, parvovirus is here to stay and continues to kill puppies who have not been vaccinated. Worse, vaccinated puppies may still contract parvovirus even if they are vaccinated while they still have antibodies that they obtained from their mother’s milk. Although every puppy gets antibodies in milk, and these antibodies are important to protect the puppy from infectious disease while the pup is very young, these maternal antibodies can also interfere with vaccination by neutralizing the viral proteins that are inoculated during the vaccination. Because puppies lose their maternal antibodies at different rates, it is difficult to know whether a young puppy still retains maternal antibodies at the time he’s vaccinated. For this reason, vaccinating puppies against parvovirus several times during puppyhood is critical. The hope is that if maternal antibodies neutralized the first vaccine, the next vaccination will have the desired effect of stimulating the puppy to make his own antibodies.
Puppies should receive their first vaccinations against parvovirus at 5 to 7 weeks of age. They then should receive booster shots every three to four weeks until they have had at least three shots. Your veterinarian will provide you with a schedule for your puppy’s vaccinations. Stick to the schedule as closely as possible. The virus is very stable in the environment and can survive for months on inanimate objects such as clothing and floors, making it even more important to vaccinate your dog against this virus.
Kennel cough got its moniker for obvious reasons: Dogs commonly contract it from other dogs in kennels, and it causes coughing. Some vets are beginning to prefer the term canine cough, as your dog doesn’t have to be in a kennel to contract it.
Kennel cough, also called infectious tracheobronchitis, can be caused by a single virus or a combination of viruses, particularly canine adenovirus-2 and canine parainfluenza virus. A bacterium called Bordatella bronchiseptica also can cause kennel cough alone or in combination with one or more of the viruses. Sometimes the viral infection impairs the normal defense systems of the lung, allowing bacteria to enter the lung, replicate, and cause pneumonia.
Dogs infected with kennel cough have a dry, hacking cough that often has a honking sound. At the end of a series of coughs, the dog may gag or retch so severely that it seems as if the dog will vomit. Indeed, sometimes the dog brings up a little frothy material at the end of the cough. The coughing worsens if the dog is exercised or becomes excited. Dogs may also have a watery discharge from the nose or eyes. Kennel cough itself lasts from seven to ten days, and dogs recover without treatment. If a dog contracts a secondary bacterial pneumonia, however, the results can be much more serious and, without treatment, can result in death.
The infection is highly transmissible between dogs and can spread like wildfire through dogs in a kennel or at a dog show (hence the kennel part of its name). Dogs are infectious before they show signs of coughing, and sometimes even after they have recovered, so it is hard to prevent transmission.
The best prevention for kennel cough is vaccination. Because several agents can cause this infection, vaccination is not foolproof, but vaccinated dogs who do become infected usually have milder symptoms. The most effective vaccination protects against parainfluenza virus and Bordatella, and is instilled into the nose of the dog. This vaccine consists of a live virus that has been modified so that it cannot cause severe disease. It can, however, cause a mild cough for a few days after vaccination, and can even be transmitted to other dogs during that time. Because of these side effects, however mild, most veterinarians suggest vaccination only for dogs who are at high risk for infection. This category includes dogs who regularly go to dog shows, are boarded at kennels, attend doggie daycare, or commonly have contact with other dogs.
If your dog has a persistent hacking cough for more than 24 hours, call your veterinarian instead of going to the clinic. The doctor then can decide over the telephone whether you should come to the clinic and risk transmitting this highly contagious infection to other dogs in the waiting room or hospital. If he decides it is a case of kennel cough, he may want to examine the dog, prescribe some cough suppressants, and advise you to have your coughing canine rest for seven to ten days until she is better. If your dog is not eating or is lethargic, she may have a secondary bacterial infection. Your veterinarian will want to examine her and will probably prescribe antibiotics or an injection and other supportive care.
Some evidence suggests that Bordatella can be transmitted from dogs to immunosuppressed individuals, such as people who are taking immunosuppressive drugs after transplants or to fight cancer, or people suffering from AIDS. Keeping coughing dogs away from these individuals is probably best.
Distemper is a vaccination success story. Once the scourge of the pooch population, now most people have never heard of a dog actually having this infection, because vaccination programs have been highly successful in reducing the incidence of the disease.
The canine distemper virus is particularly wily. The first thing it does after entering the body is spread in the blood to all the lymph nodes and kill the lymphocytes that reside there. Lymphocytes are the major cells for antiviral defense, so the infected dog becomes severely immunosuppressed (and at risk for many other illnesses). This action allows the virus to replicate in the lungs (and cause pneumonia) and the gastrointestinal tract (and cause diarrhea and dehydration), and even to enter the brain (and cause encephalitis, paralysis, and seizures). In addition, because the virus causes immunosuppression, infected dogs frequently contract secondary bacterial and parasitic infections that can also be life threatening.
The first signs of distemper may be a discharge from the eyes accompanied by a fever. The dog may also be coughing, exhibit weight loss, suffer from diarrhea, and lack interest in food. The signs of distemper are so varied that any young puppy who is sick should be taken to the veterinarian for a definitive diagnosis. About 50 percent of adult dogs and 80 percent of puppies who contract distemper die, and dogs who do recover often retain lifelong debilitations such as seizures, blindness, and lameness.
As with most viral infections, treatment for distemper is limited. With supportive care, some dogs can pull through, but the key to beating this disease is to prevent infection by vaccination. Inoculating puppies when they are still very young is important and effective.
Bacteria are veritable giants in comparison to viruses. You can fit only 25,000 bacteria (as compared to 25 million viruses) on the period at the end of this sentence. Bacteria differ from viruses, in that they can live on their own and don’t need a host cell to replicate.
Bacteria live in the soil, in plants, and in animals — including you. Although most species of bacteria are beneficial — or, at least, cause no harm — the following sections discuss a couple problems caused by some nasty bacteria.
Lyme disease is a tick-borne bacterial disease that was first recognized in humans in Lyme, Connecticut, in 1975 and in dogs in 1984. The Lyme disease bacterium is transmitted to your dog by the tiny deer tick (shown in Figure 2-1) and probably, although less commonly, by other species of ticks, too. Deer ticks live on white-tailed deer and white-footed mice in the wild. They are very small — no larger than the head of a pin — making them hard to see, especially in a dog’s thick coat. A dog’s greatest chance of becoming infected is from May to September, when the ticks are most active, but transmission can also occur at other times. Up to 40 percent of the deer ticks in the northeast, mid-Atlantic, north-central and Pacific coast of the United States contain the bacterium that causes Lyme disease.
Figure 2-1: Left to right: a nymph (young tick) before it has attached, an engorged nymph, an adult before attaching, and an engorged adult deer tick. All can transmit Lyme disease. (Photograph courtesy of Fred Dubbs)
Although many dogs get infected with the Lyme bacterium, only a few develop Lyme disease. Typical acute infection results in swollen joints, lameness, and muscle pain. However, the bacterium can also cause vague symptoms such as fever, loss of appetite, and lethargy, which can make infection difficult to diagnose in a timely fashion.
If your dog is suddenly lame without evidence of trauma; has a hot, swollen joint; or has a fever, especially if you know he was recently bitten by a tick, take him to the veterinarian. The vet will perform a complete physical examination and will take blood to be tested for antibodies to the Lyme bacterium.
If Lyme disease is undiagnosed or left untreated, permanent damage to the joints can occur, and the bacterium also can spread to the heart and kidneys. Infected dogs should be treated with appropriate antibiotics as soon as possible.
Prevention of Lyme disease requires a two-pronged attack. Vaccines are available to protect your dog from infection. The vaccine is unique because it actually kills the bacterium inside the tick before it ever gets a chance to enter your dog. However, as with all vaccinations, side effects may result, so discuss the pros and cons of vaccination with your veterinarian. Vaccination probably is a good idea for dogs who live in areas where Lyme disease is more common and for dogs who are frequently outdoors, like the one shown in Figure 2-2.
Figure 2-2: Dogs who work or play outdoors are exposed to ticks and are at higher risk for contracting tick-borne infections such as Lyme disease.
The second part of your Lyme disease prevention plan is to try to ensure that your dog doesn’t become exposed to the Lyme bacillus. Apply a product that repels ticks before your dog goes out for an adventure in the wild outdoors. Use a product your veterinarian recommends — repellents purchased at pet stores and grocery stores frequently are not as effective. Examine your dog daily for ticks during the spring and summer months, and remove them gently. To remove a tick, use tweezers to grab the insect as close to your dog’s skin as possible, and pull straight out, without squeezing or twisting.
Leptospirosis is another disease that, like distemper, used to be a major dog killer but has been very uncommon during the past three decades. We can thank effective vaccines for that. In the last three years, some unusual strains of leptospirosis were diagnosed in an increasing number of dogs. Veterinary scientists went to work and have now designed new vaccines to be effective against these canine killers.
Leptospirosis is caused by any one of about 200 different but related strains of bacteria. The bacteria infect many different species of wild and domesticated animals, including raccoons, skunks, opossums, and cattle. The infected animal sheds large numbers of bacteria in urine. Leptospira bacteria are specialists in water survival, so if the urine drains into standing water, these bugs can survive for a long time, just waiting for your dog to come along and have a drink. The bacterium then enters the blood stream and travels throughout the body to many tissues, where it replicates and causes damage. Leptospira particularly like to grow in the kidney and can cause severe renal failure in dogs. Of course, by replicating in the kidney, the bacteria has easy access to the urine so that it can be expelled to the environment and infect another unsuspecting animal. Pretty ingenious, huh?
The signs of disease in dogs include a sudden onset of fever or trembling, lethargy, nausea, jaundice, vomiting, and diarrhea. If the dog is not quickly treated with antibiotics, she may stop producing urine and hemorrhage into the lung and intestine. Luckily, with antibiotics and supportive care, most dogs recover, but complete recovery may take several weeks.
Leptospirosis also infects humans. Most people, just like dogs, get infected by exposure to urine from wildlife or farm animals. However, it’s also possible for dogs to transmit the infection to their people. In areas where leptospirosis outbreaks are occurring, keep pets away from children’s play areas, including sandboxes and wading pools.
Rickettsia: What a racket!
Rickettsia are poorly understood organisms that are intermediate in size, between viruses and bacteria. They live inside cells like viruses do, but they are susceptible to some of the antibiotics that kill bacteria. The two main rickettsial diseases of dogs are Ehrlichiosis and Rocky Mountain spotted fever. Both are carried by those diabolical disease-delivery units — ticks.
Ehrlichiosis and Rocky Mountain spotted fever are both characterized by fever, rashes, anemia, hemorrhages, and joint and muscle pain in dogs. If your dog is ill for more than 24 hours, particularly if you know a tick has bitten him, it’s a good idea to have a veterinarian give him the once-over. Only a vet can differentiate between these two diseases, which can appear quite similar clinically. Blood tests are required to make a definitive diagnosis, and even they aren’t foolproof. Treatment of rickettsial infections requires antibiotic treatment for six to eight weeks.
Fighting the Fungus among Us
There’s a lot more to fungi than the fact that one of them provides a common pizza topping. Fungi inhabit soils throughout the world. Some inhabit the soil of the Mississippi Valley, the mid-Atlantic states, and southern Canada; others grow in soil contaminated with bird or bat excrement; and still others call the dry Southwestern soils home. Active dogs who spend a lot of time running outdoors (like the hunting dog in Figure 2-3), especially dogs who love to dig, risk becoming infected with fungal organisms that live in the soil. Usually a strong immune system will keep these bad bugs at bay. But if the dog is battling another infection or has a weak immune system, these organisms can get a foothold in the dog’s body and cause serious disease.
These fungal agents cause arthritis, pneumonia, infections in bones, and signs of systemic infection such as fever, loss of appetite, and malaise. No vaccines are available for these organisms. If you live in an area where fungi are present, the best way to prevent infection is to keep your dog from digging, especially around the holes of burrowing animals where the fungi are especially abundant. Also keep your dog away from areas frequented by large numbers of bats or birds.
Figure 2-3: Hunting dogs like Flyer are exposed to fungal organisms in the soil.
Parasites are the ultimate opportunists, living on the skin, in the intestine and just about anywhere they can gain a foothold. Luckily, with today’s excellent veterinary preventive medicine programs, dogs don’t have to suffer parasitic infections. Parasite control is also important because some of them (roundworm and hookworm) can spread to humans.
Fleas are the bane of a dog’s existence. They make him itch, itch, itch. And the more a dog scratches, the itchier he seems to get. These irritating insects can cause itching in two different ways. First, they bite on a big chunk of skin and start sucking blood. They stay at one spot until they are full, or hop around, drinking at many different sites. Worse, they often bite in thin-skinned, sensitive areas such as near the ears, at the base of the tail, and in the groin area. Flea bites are irritating enough, but many dogs actually develop an allergic reaction to the saliva of the fleas and become extremely itchy all over, even with the bite of only one flea. Sometimes the allergy is so severe that a dog will chew at himself until he loses big patches of hair, bleeds, and ultimately develops thick, crusty skin, especially on his feet, at the base of his tail, and around his back legs.
If you see your dog scratching vigorously or biting aggressively at himself, it’s time for a bug check. Start by looking around your dog’s ears, at the base of his tail, and on his tummy. Part the hair and look for brown, flat, oval bugs about 1⁄8 inch long. Keep your eyes peeled, because a startled flea can jump quickly into the air and land several inches away. Frequently, you won’t actually see a flea, but you can see flea dirt stuck in the dog’s hairs. Flea dirt is a polite term for flea excrement, a crumbly black material that consists mainly of digested blood. You can identify flea dirt by placing a drop of water over the dirt, letting it soak up the water for a minute or two, and then smearing the dirt on a piece of white paper towel. A reddish smear confirms that it is, in fact, flea dirt.
If you identify a flea or flea dirt, leap into action. The only thing that will give your dog relief is ridding his body and your house of those pesky pests. You’ll be delighted to know that the solution may entail giving your dog a hot bath with anti-flea shampoo, applying an anti-flea treatment between his shoulder blades, administering pills, vacuuming every inch of your apartment or house, and spraying along the floorboards with another anti-flea product. With the many safe anti-flea products available today, your dog no longer has reason to suffer.
Fleas are especially fond of cats, so if you share your digs with an animal of the feline persuasion, be sure to include her in your flea prevention and treatment protocol.
Ticks are major pests not only because they can bite your dog and cause local skin irritation, but because they carry a host of other pesky germs that can make both you and your dog sick (including the already-discussed Lyme disease). Ticks live on long grasses and shrubs, and they have a sticky substance on their bodies that enables them to easily cling to the fur of passing animals such as your dog. They then crawl down the hair to the skin and latch on, taking a big bite. They suck blood for hours and even days until they are full to bursting. During this time, they can transmit whatever infectious organisms they happen to be carrying.
If you live in an area where ticks are prevalent (most of the United States, except the Southwest and Alaska), check your dog for ticks every day, at least during tick season — usually the spring and summer months, but sometimes later depending on warm weather. Carefully remove every tick you find (see the earlier coverage of Lyme disease).
If your dog enjoys the outdoors (and most dogs do), apply a product that prevents ticks from attaching to the skin. Be sure to get advice from your veterinarian on which product is best, because new products enter the market all the time. Also continue to check your dog from head to toe every time he comes in from outside. You’re most likely to find ticks around your dog’s face, eyes, and ears, although they really can be anywhere. Be sure to look inside the ears, too!
Dozens of kinds of worms can set up shop in your dog’s body, often in the intestine. Puppies are especially susceptible to infections with worms, because some species of worms are transmitted from the mother before the puppy is even born. For this reason, deworming puppies is very important (see Chapter Preventing and Treating Diseases: Working with Your Vet
The general level of care for dogs these days is so high, however, that adult dogs rarely have problems with worms (with the exception of tapeworms). Nonetheless, it is a good idea to bring a fecal sample to your annual veterinary visit every year, just to be sure.
If you adopt a dog from a shelter or find a stray, be sure to have her checked for worms, because you won’t know whether she has had adequate veterinary care from puppyhood.
Being Aware of Which Bugs Infect Humans
Just as we share our lives with dogs, we sometimes share our infections, too. Be aware of the potential transmission of organisms from dogs to humans, called zoonosis, so you can take preventive measures. The most important zoonotic disease in dogs is rabies, but dogs can unwittingly share many infectious organisms with us, including leptospirosis, roundworms, and hookworms.
Humans also can be infected by the canine roundworm Toxocara canis. If a human accidentally ingests Toxocara eggs, the eggs will hatch and larvae will migrate through the body, causing fever, rash, and cough. This condition is called visceral larval migrans. If the worm larvae migrate to the eye, they can cause blindness. Larvae can migrate through the spinal cord and brain, causing severe neurologic disease, too. These infections usually occur in children who live in conditions of poor sanitation. Toxocara eggs must mature in the environment for one to three weeks before they are infectious, so humans don’t become infected by handling dogs directly. They must contact eggs in the environment. Toxocara eggs are very hardy, however, and can survive in the environment for weeks or months.
Consider these tips to prevent human infection with Toxocara:
– Deworm all puppies, regardless of whether Toxocara eggs are detected in fecal samples, twice (21 days apart) during their initial vaccination period. Have the vet check multiple stool samples during puppy visits. Use a monthly heartworm prevention that deworms for roundworms.
– Do not allow children to play where dogs defecate.
– Always clean up after your dog in public places. And always wash hands with hot water before eating.
Several other infectious organisms can be transmitted from dogs to humans, but they infect only immunosuppressed humans, such as people undergoing cancer treatment or organ transplantation, and individuals with AIDS. If you are immunosuppressed and want to have a dog, your best bet is to get a clinically normal adult dog from a private family. If this is not possible, have a veterinarian give the prospective four-legged family member a thorough physical examination, complete with fecal and blood tests.
Intestinal parasites are dangerous. It’s very important that people who own dogs understand this fact about common intestinal parasites — roundworms, hookworms, whipworms, tapeworms, and to a lesser degree coccidia. Always follow the advice of your vet regarding deworming, even if a stool sample is negative.
by Eve Adamson, Richard G. Beauchamp, Margaret H. Bonham, Stanley Coren, Miriam Fields-Babineau, Sarah Hodgson, Connie Isbell, Susan McCullough, Gina Spadafori, Jack and Wendy Volhard, Chris Walkowicz, M. Christine Zink, DVM, PhD