Infectious Diseases - Healthy Dog Experts

Infectious Diseases are caused by bacteria, viruses, protozoa, fungi and rickettsia that invade the body of a susceptible host and cause an illness. They are transmitted from one animal to another by contact with infected urine, feces and other bodily secretions or by inhaling pathogen-laden droplets. They may also be acquired by contact with spores in the soil that enter the body throughout the respiratory tract or a break in the skin. A few are sexually transmitted. Although pathogens exist everywhere in the environment, only a few cause infection. Fewer still are contagious. Many infectious diseases are species-specific. For example: a dog cannot catch a disease that is specific to a horse and vise-versa. Other infectious diseases are not species-specific and are capable of causing disease in many animals, including humans. Many infectious agents are able to survive for long periods outside the host animal.

Brucellosis

This disease is caused by the bacteria Brucellosis canis. It is a major cause of sterility and spontaneous abortion in dogs. Puppies effected in utero are typically aborted at 45 to 59 days after conception. Suspect this disease in any bitch who aborts two weeks before she is due to deliver and whenever a bitch delivers stillborn puppies or puppies who sicken and die. Dogs with acute infection have enlarged lymph nodes in the groin and/or beneath the jaw. Fever is rare. The testicles of the male may swell in the initial stages and then become smaller and atrophic as the sperm producing cells are destroyed. Note: however, that this disease can infect a dog or bitch without producing any signs of illness. In a dog with an acute infection, bacteria are found in the blood, urine, body secretions and the products of abortion. In a dog with a chronic or inactive infection, bacteria can be transmitted in vaginal secretions during estrus and in semen. The most common mode of transportation is by contact with infected vaginal discharges following a spontaneous abortion and by contact with the urine of infected dogs. The disease can spread rapidly throughout a kennel in this manner. Males can aquire the disease through oral and nasal contact with the vaginal secretions of estrus females. Females can aquire the disease through breeding with an infected male. This is of particular concern to breeders, because males can harbor the bacteria for life. A positive blood culture obtained during an acute infection is the most conclusive diagnostic test. Bacteria can also be cultured from aborted tissue. Blood serum tests will determine if a dog has ever been infected.

Leptospirosis

Canine leptospriosis is caused by an order of bacteria called spirochetes-slender, spirally undulating bacteria. There are at least four species of the leptospira bacteria (or serovars) that can infect dogs: canicola, icterohemorrhagae, grippotyphosa & pomona. Leptospira are found in wild and domestic animals. The bacteria are spread through the urine, often making their way into water sources and remaining effective in the soil for up to six months. Rats, pigs, racoons, cattle, skunks and opossums appear to be the primary reservoirs. With housing spreading into the suburbs, more wildlife are coming into contact with pet dogs. This may be the cause of the upswing in leptospirosis cases. Spirochetes enter a dog's system through a break in the skin or when the dog drinks contaminated water. Dogs who spend a lot of time in the water are at increased risk, as are dogs who drink who drink out of puddles and dogs who spend time in yards that get a lot of runoff or stays wet after it rains. Most infections are mild and do not show clinical signs. Signs appear 4 to 12 days after exposure. Fever is present in the early stage. Other signs are loss of appetite for several days, vomiting, lethargy, depression, muscle pain and sometimes diarrhea or blood in the urine. Leptospirosis primarily effects the kidneys and/or the liver. In severe cases, the whites of the dogs eyes turn yellow (jaundice). This indicates hepatitis with destruction of liver cells. Coagulation problems can ensue, with spontaneous bleeding from the mouth and blood in the stools. Following recovery, untreated dogs can become carriers and spread bacteria in their urine for up to a year. The canicola and grippotyphosa servars tend to cause kidney damage and the pomona and icterohemorragiae serovars most often effect the liver. Young dogs tend to show liver damage with all of the serovars. The diagnosis can be suspected based on the dog's clinical signs. Tests of liver and kidney function will be abnormal. Spirochetes can be detected in the urine and blood by the flourescent antibody staining. Blood tests are available to confirm the diagnosis.

Bordetella Bronchiseptica

Bordetella Bronchiseptica bacteria are frequently found in dogs with the kennel cough complex and other respiratory diseases. Signs of upper respiratory illness caused by bordetella include a dry hacking cough accompained by a clear nasal or eye discharge. In puppies and immune-compromised adult animals secondary bacterial invasion of the lower respiratory tract following viral illness may cause life threatening pneumonia. Dogs who are carrying the organism and may not even be ill themselves, may still cough or exhale the organism into the air. Healthy dogs can then be infected by breathing in that contaminated air. The bacteria can be cultured from nasal swabs or transtracheal washings.

Several bacteria of the salmonella species are capable of producing acute infectious diarrhea in dogs. Salmonella remain alive for many months in soil or manure. In dogs, the disease is aquired by consuming raw or commercially contaminated foods, by eating animal manure or by making oral contact with surfaces that have been contaminated by the diarrhea of an infected dog. This bacterial infection is a risk in dogs fed a raw diet. Puppies and young adults are most suseptable, as are dogs natural resistance has been compromised by a viral infection, malnutrition, parasites or being housed in crowded, unsanitary quarters. Signs of illness include fever, vomiting and diarrhea. The stool may be bloody and foul smelling. Dehydration develops when vomiting and diarrhea are prolonged. Bacteria in the bloodstream can cause abscesses in the liver, kidneys, uterus and lungs. The acute illness, which lasts four to ten days, may be followed by chronic diarrhea that persists for more than a month. Dogs with chronic diarrhea shed salmonella in their feces and are a potential source of infection to other animals and humans. The diagnosis is made by identifying salmonella bacteria in stool cultures when the dog is in the carrier state, or in the feces, blood and infected tissues of dogs suffering from acute infection.

Campylobacteriosis is a disease that produces acute infectious diarrhea in puppies. It also occurs in kennel dogs and strays - most of whom are in poor condition and are suffering from other intestinal infections. The bacteria is aquired by contact with contaminated food, water, uncooked poultry or beef and animal feces. Campylobacteria can survive for up to five weeks in water or unpasteurized milk. The incubation period is one to seven days. Signs of acute infection include vomiting and a watery diarrhea that contains mucus and sometimes blood. The disease usually runs it's course in five to fifteen days, but may be followed by chronic diarrhea in which bacteria is shed in the feces.

Colibacillosis is an infectious diarrhea caused by the bacteria E. coli. There are some strains of E. coli that are not part of the normal intestinal flora. When ingested, these strains are capable of producing acute diarrhea. E. coli. can be aquired from infected drinking water, food or fecal matter. This bacterial infection is a risk in dogs fed a raw diet.E. coli is an important cause of puppy septicemia, and may also cause urinary tract or reproductive tract infections. In dogs of all ages, a concurrent viral infection of the intestinal tract can allow E. coli to become pathogenic and produce a life-threatening illness.

Lyme Disease

Lyme disease is caused by the spirochete bacteria Borrelia burgdorferi. The spirochete is aquired through a bite from an infected tick. Lyme disease is now regarded as the most common tick-borne illness in the United States. This disease was first recognised in 1975, following an outbreak of what appeared to be acute arthritis in several rural communities in south eastern Connecticut, including the town of Old Lyme. Currently, most cases are found in wooded locations in the Northeast, upper Midwest (including much of Wisconsin and Minnesota), northern California amd the Pacific Northwest. The white footed mouse is the principle reservoir for the spirochete. Birds can also harbor it. The white tailed deer supports the tick, but not the spirochete. Lyme disease is spread primarily during tick season (May thru August), peaking in the month of july, but ticks can be active anytime the temperature is over 32 degrees fahrenheit - (0 degrees celsius). The disease in dogs is most commonly characterized by the sudden onset of lameness. In fact, lameness is often the only sign of infection. One or more joints may become swollen and painful to the touch. Some dogs run a fever and experience weakness, lethargy, loss of appitite and weight loss. The lameness may only last a few days, but in some cases it becomes chronic and persists or re-occurs for months. Kidney problems are the next most common sign. An acute cardiac syndrome is quite rare. Both these syndromes are usually fatal. Most dogs exposed to lyme disease do not become ill. Serological blood tests will indicate wether a dog has been exposed to the disease. Dogs may not test positive for a few weeks after exposure. New serologic test can distinguish between dogs with vaccine immunity and dogs with natural exposure. A rising antibody titer in the absence of recent vaccination, however, indicates active infection. Western Blot and ELISA blood test are now both used to detect exposure. Many dogs who test positive for lyme disease will also have other tick-borne diseases, such as ehrlichiosis and babesiosis. X-rays of swollen joints show fluid without degenerative joints changes. Synovial fluid analysis (in which a needle is inserted into a joint to remove fluid for examination) may show spirochetes.

Distemper

Distemper is a highly contagious disease caused by a virus similar to the one that causes measles in people. Worldwide,it is the leading cause of infectious disease deaths in dogs, although in the United States it occurs only sporadically. Infected animals shed canine distemper virus in all body secretions. Inhaling the virus is the primary source of exposure. Half the dogs who become infected with canine distemper virus show mild signs of illness or no signs at all. The overall health of the dog has a lot to do with how ill he becomes. The disease is most severe in dogs who are poorly nourished and ill-kept. The distemper virus tends to attack brain cells and cells that line the surfaces of the body, including the skin, the conjunctiva, the mucous membranes of the respiratory tract and the gastrointestinal tract. The disease takes a variety of forms. Secondary infections and complications are common, partle attributable to the immuno-suppressive effects of the virus. The first signs of distemper appear in six to nine days after exposure, and in mild cases, go unnoticed. First stage: is characterized by a fever spike of up to 103 to 105 degrees fahrenheit (39.4 to 40.5 degrees celsius). A second fever strike is accompanied by loss of appetite and a watery discharge from the eyes and nose. These symptoms may be mistaken for a cold. Within a few days, the eye and nasal discharge becomes thick, yellow and sticky. The dog develops a pronounced dry cough. Pus blisters may appear on the abdomen. Vomiting and diarrhea are frequent and may cause severe dehydration. During the next one to two weeks, very often the dog seems to be getting better, but then relapses. This often coincides with the end of the course of antibiotics (antibiotics are not recommended unless absolutely neccessary) and the development of gastrointestinal and respiratory complications due to secondary bacterial invasion. Second stage: occurs two to three weeks after the onset of the disease. Many dogs develop signs of brain involvement (encephalitis), characterized by brief attacks of slobbering, head shaking and chewing movements of the jaws (as if the dog were chewing gum). Epileptic-like seizures may occur, in which the dog runs in circles, falls over and kicks all four feet wildly. After the convulsive episode the dog appears to be confused, shies away from his owner, wanders about aimlessly and appears to be blind. In cases with brain involvement in which the diagnosis is uncertain, a spinal tap and analysis of cerebrospinal fluid may be of assistance. But this is not always diagnostic. Another indication of brain involvement is distemper myoclonus, a condition characterized by rythmic contractions of muscle groups at up to sixty contractions per minute. The jerking can effect all parts of the body, but is most common in the head. Myoclonus is first seen when the dog is resting or sleeping. Later it occurs both day and night. Pain accompanies myoclonus, and the dog whines and cries. If the dog recovers, the jerking jerking continues indefinitely-but becomes less severe in time. Hard pad: is a form of distemper in which the virus attacks the skin of the nose and feet, producing thick, horny skin on the nose and calluslike pads on the feet. It first appears about 15 daysafter the onset of the infection. At one time, hard pad and encephalitis were thought to be separate diseases, but now they are recognized as being caused by different strains of the distemper virus. Hard-pad is much less common than it was in the past due to better vaccines and natural remedies.

Canine herpesvirus is wide spread in the dog population and produces a variety of illnesses. It causes a fatal disease in newborn puppies. It is one of the agents implicated in the kennel cough complex. It causes vaginitis in bitches and infection of the penile sheath in males, and it can be transmitted between males and females during breeding. Bitches with vaginitis develop hemorrhagic areas and blisterlike lesions of the vaginal mucosa. These lesions may reappear when the bitch comes into heat. Intrauterine infections that progress from the vagina are associated with early embryonic loss, abortions and stillbirths. Herpesvirus infection can be confirmed by isolating the virus from infected tissue.

Infectious canine hepatitis is a highly contagious viral disease caused by canine adenovirus-1. In the United States the disease is rare and is seen almost exclusively in wild canids and unvaccinated dogs. Most cases occur in puppies under 1 year of age. Following exposure, the virus multiplies in the dog's tissues and is shed in all body secretions. During this stage, the dog is highly contagious and can spread infection to other dogs who make contact with his infected urine, stool and saliva. After he has recovered, the dog remains infected and sheds the virus in the urine for up to nine months. Infectious canine hepatitis effects the liver, kidneys and the lining of the blood vessels, producing a mild infection at one extreme to a rapidly fatal infection at the other. A dog with a mild or subclinical infection loses his appetite and simply appears lathargic. In the fatal form, the dog suddenly becomes ill, develops bloody diarrhea, collapses and dies within hours Puppies may die without obvious illness. A dog with acute infection runs a fever up to 106 degrees Fahrenheit (41.1 degrees Celsius), refuses to eat, passes bloody diarrhea and often vomits blood. The dog has a tucked-up belly caused by painful swelling of the liver. Light is painful to the dog's eyes and causes tearing and squinting. Tonsilitis, spontaneous bleeding beneath the gums and under the skin and jaundice may occur. Infectious hepatitis can be suspected by the signs and symptoms and confirmed by virus isolation tests. About 25% of dogs recovering from infetious canine hepatitis develop a characteristic clouding of the cornea of one or both eyes known as blue eye. In most cases blue eye disappears within a few days.

Rabies

The major wildlife reserviors for rabies (with substantial overlap) are the skunk in the Midwest, Southwest and California; racoons in New England and the East; foxes in New York, neighboring eastern Canada, Alaska and the Southwest; and coyotes and foxes in Texas. Bats , which are distributed widely, also carry rabies. The main source of infection for humans outside the United States continues to be a bite from an infected dog or cat. In India for example: a country that lacks an effective rabies control program, it is estimated that several thousand people die of rabies each year. Travelers to countries where rabies is endemic should be aware of the risk of dog bites. The rabies virus, which is present in infected saliva, enters the body at the site of a bite. Saliva on an open wound or disrupted mucous membrane also constitutes exposure. The average incubation period in dogs is two to eight weeks, but it can be as short as one week, or as long as one year. The virus travels to the brain along the nerves. The more distant the bite is from the brain, the longer the period of incubation. The virue then travels back along the nerves to the mouth. Entry into the salivary glands occurs less then ten days before symptoms occur-which means animals can be infectious before they show any signs of rabies (this is unusual but is possible). Dogs can show either two versions: The aggressive form, they attack and act very bodly aggressive; or the "dumb" form where they are ataxic (an inability to coordinate voluntary muscle movements) and may walk into objects. In both cases, you may notice extensive drooling due to paralysis of the muscles used for swallowing. Any dog who is bitten by an animal who is not absolutely known to be free of rabies must assume to have been exposed to rabies, until proven otherwise.

Kennel Cough is, in fact, not one but a group of highly contagious respiratory diseases of dogs that spread rapidly though a kennel or other area where many dogs are kept in close quarters. A harsh, dry cough is the characteristic sign of infection. The cough may persist for many weeks and become a chronic problem as the virus is replaced by secondary bacteria invaders. A number of viruses and the bacteria Bordetella bronchiseptica, have been implicated in the kennel cough complex.

Canine parvovirus is an acute, highly contagious disease of dogs that was first described in the early 1970's. The virus had a tendency to attack rapidly reproducing cells, such as those lining the gastrointestinal tract. The virus is shed in large amounts in the stools of acutely infected dogs for up to several weeks following infection. The disease is transmitted by oral contact with infected feces. Parvo can be carried on the dogs hair and feet, as well as on contaminated crates, shoes and other objects. When the dog licks the fecal material off hair, feet or anything that came into contact with infected feces, he aquires the disease. Parvo effects dogs of all ages, but most cases occur in puppies 6 to 20 weeks of age. Doberman Pinschers and Rottweilers appear to aquire the infection more readily and experience more severe symptoms. The reason for lower resistance in these breeds is unknown. Following an incubation period that averages 4 to 5 days, the acute illness begins with depression, vomiting and diarrhea. Some dogs have no fever, while others may have high fevers up to 106 degrees Fahrenheit (41.1 degrees Celsius). Pups with severe abdominal pain exhibit a tucked-up abdomen. Diarrhea is profuse and contains mucus and/or blood. Dehydration develops rapidly. Suspect parvo in all pups with the abrupt onset of vomiting and diarrhea. The most efficient way to diagnose parvo is to identify either the virus or virus antigens in stools.

Canine coronavirus is a contagious intestinal infection that usually produces a mild disease. However, it can be severe in young puppies and dogs who are stressed by concurrent infections. The distribution is worldwide, and dogs of all ages are effected. Coronavirus is transmitted by contact with infected oral and fecal secretions. Following infection, the virus is shed in the stool for many months. Symptoms vary from none (the most common form) to outbreaks of acute diarrhea, typically occuring in a community of dogs. Dehydration can occur if the diarrhea is severe. The early signs of the illness is depression with loss of appetite, followed by vomiting and the passage of a foul-smelling, yellow to orange colored diarrhea that varies from soft to watery. The diarrhea may contain blood. Unlike parvovirus, fever is not common. There is no readily available test to diagnose coronavirus during the acute illness. A rise in antibody titer in serum tested at the time of illness and two to six weeks later can provide a retrospective diagnosis.

Fungi are a large family that includes mushrooms. They live in soil and organic material. Many types of fungi spread via airborne spores. Fungus spores, which resist heat and can live for long periods without water, gain entrance through the body through the respiratory tract or a break in the skin. Fungal diseases can be devided into two catagories. There are fungi that effect only the skin or mucous membranes, such as ringworm and thrush. In the other catagory, the fungus is wide spread and involves the liver, lungs, brain and other organs, in which case the disease is systemic. Systemic fungal diseases are not common in dogs. They tend to occur in chronically ill or poorly nourished animals. Prolonged treatment with steroids and/or antibiotics may also change the dog's pattern of resistance and allow a fungal infection to develop. Good hygiene is important when handling and caring for a dog with any fungal infection. The risk to humans is low, but these are difficult diseases to treat.

This disease is found in the central United States near the Great Lakes, the Appalachian Mountains, Texas, and the valleys of the Mississippi, Ohio and Missouri rivers. These areas have nitrogen-rich soil that facilitates growth of the causative fungus (histoplasma capsulatum). Spores are found in soil contaminated by the feces of bats, chickens and other birds. Spores are breathed in by dogs, peopls or other animals. In most cases, histoplasmosis is subclinical or inapparent, occasionally producing a mild respiratory infection. There is an acute intestinal form, however, that attacks the small bowels and colon. The principal signs are weight loss, vomiting, muscle wasting, coughing, enlargement of the tonsils and other lymph nodes, as well as involvement of the liver, bone marrow, spleen, eyes, skin and rarely the brain. The diagnosis is made by chest X-rays, blood studies and identification of the histoplasma organism in cytology, biopsy or culture specimens.

This is the most severe and life-threatening of the systemic fungal diseases. Coccidioidomycosis is found in dry, dusty parts of the Southwestern United States, and in California and neighboring Mexico. (Note: that coccidioidomycosis is not the same disease as coccidiosis, disease caused by intestinal protozoa). Infection occurs by inhaling spores. Most cases are subclinical or inapparent. A severe form affects the lungs and produces acute pneumonia. If the disease becomes systemic, it may involve the long bones (most common), liver, lymph nodes, spleen, skin and brain. Affected dogs will often have a chronic cough, weight loss, fever and lameness. The diagnosis is made by identifying the organism (Coccidioides immitis) in cytology, biopsy or culture specimens.

This disease, caused by the yeastlike fungus Crytpococcus neoformans, is aquired by inhaling spores found in soil contaminated by bird droppings, especially those of pigeons. In dogs, cryptococcosis involves the brain, eyes, skin and lymph nodes. About 50% of the dogs with this fungus will also show respiratory signs. Signs of brain involvement are an unsteady gait, pressing the head against a hard surface or standing with the head up against a wall, circling, seizures, blindness and dementia. Involvement of the inner structures of the eyes leads to blindness. In the less common form that infects the skin, cryptococcosis produces firm nodules, primarily in the head area, that ulcerate the drain pus. The diagnosis is made by fungal culture and/or tissue biopsy. A cryptococcus latex agglutination test is available.