Contagious infectious diseases

These are caused by bacteria or viruses. Vaccines are available against the majority of these diseases. They are often fatal without treatment or in unvaccinated animals.

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This is a contagious disease caused by bacteria from the Leptospira genus; it can affect all domestic animals and is transmissible to man. In the dog, several groups, known as serotypes, are highly pathogenic, including Leptospira icterohæmorragiæ and Leptospira canicola. These diseases are found worldwide with variable serotypes from one region to the next, and a predilection for wet areas and kennels.

The clinical symptoms of leptospirosis vary depending on the serovar present. At first, the dog may have haemorrhagic gastroenteritis, which can be caused by either of the serovars mentioned above. This is a severe form of gastroenteritis: after an incubation period of five days, the dog is exhausted and prostrate with anorexia and polydipsia (increased thirst). It will have a high fever for two or three days, followed by an abnormally low body temperature. Palpation of the abdomen is extremely painful.

The following clinical phase lasts about five to six days. During this period, gastrointestinal symptoms appear (bloody vomit and diarrhoea), as well as haemorrhagic patches on the mucous membranes and skin, inflammation of the oral mucosa (which smells extremely unpleasant) and acute kidney failure (reduced urine production, sometimes tinged with blood). Nervous, visual, cardiac and pulmonary symptoms may also be observed. This phase is followed by coma then death.

Gastroenteritis may be present in a peracute (very severe) form leading to death within 48 hours, after a period of hypothermia accompanied by vomiting and diarrhoea then coma. A less acute form is also possible, which lasts about two weeks, in which the dog may recover after the gastroenteritis phase.

A second form of leptospirosis known as icteric leptospirosis (infectious jaundice) also exists. It is caused exclusively by Leptospira icterohaemorrhagiae. The incubation period lasts between 5 and 8 days, giving way to fever for two days, followed by hypothermia, exhaustion and abdominal pain. The dog becomes anorexic. During the following clinical phase the mucosae take on the reddish-orange colour characteristic of jaundice. The jaundice is accompanied by diarrhoea and vomiting. This form leads to death in 5 to 15 days.

© Diffomédia/Royal_Canin

A third form of the disease, leptospiral nephritis, is caused byLeptospira canicola. There are two forms: a rapid form in which gastroenteritis predominates, and a slow form, which is usually not discovered until its final stage with uraemia (a significant increase in the urea concentration in the blood). The dog dies after falling into a uraemic coma.


River or pond water and objects soiled by urine may lead to indirect contamination.


Leptospirosis is diagnosed on clinical examination of the animal. The symptoms are fairly characteristic. Laboratory analysis can be used to detect leptospires in the blood before the 8th day of the disease, and thereafter in the urine. Circulating antibodies are not present until after the 10th day of the disease and cannot therefore be detected in the blood until then.

Dogs may contaminate themselves or each other by biting, licking or coming into contact with contaminated dead animals. River or pond water and objects soiled by urine may lead to indirect contamination. The leptospires enter the body via the mucous membranes or through wounds in the skin. Sources include the excreta and secretions of diseased animals, blood in the early stages of infection and urine for several months after the 8th day. Dogs suffering from less acute and chronic forms of the disease can be treated with certain antibiotics. Preventive measures include preventing water contamination, disinfection of the premises and rodent control; the latter act as vectors, particularly rats, hedgehogs and voles. Vaccines are available and provide relatively good immunity with a maximum duration of six months; they should be used in high-risk areas.

Dogs can transmit these leptospires to man, thus presenting a public health risk. It is therefore classified as a zoonosis. In man the disease causes jaundice similar to that seen in the dog.

Infectious tracheobronchitis (Kennel Cough)

This disease is a contagious respiratory disease, characterized by a cough which can last for several weeks. The syndrome is caused by a combination of bacteria and viruses, and is primarily encountered in group situations (kennels) in which dogs of various origins are brought together. It is also seen in isolated animals, for example after a dog show. The main culprit is the Bordetella bronchiseptica bacterium. It often appears at the same time as a viral infection. The dog’s general health is not affected. After an incubation period of about three days, the dog begins to cough and a purulent nasal discharge appears. Different viruses may cause the various symptoms. Canine parainfluenza virus may provoke mild inflammation of the nasopharyngeal region and a cough that lasts for a few days. This virus is highly contagious and can be transmitted to other dogs in the vicinity. Finally, various Mycoplasma may exacerbate the effects of other microorganisms, although alone they do not cause symptoms.

The most common clinical symptom of kennel cough, tracheobronchitis, is uncomplicated. It causes a severe cough that is dry, harsh, non-productive and persistent. The symptoms may disappear within a week or last for several weeks in more serious forms of the illness. Associated symptoms include inflammation of the conjunctivae, sinuses, tonsils and pharynx. The dog’s general health is not usually affected.

© Duhayer/Royal Canin

In rare cases, in dogs with immunodepression, a more serious form of the illness develops, leading to pneumonia and deterioration in general health (exhaustion, anorexia and fever). This form develops progressively over a short period.

Diagnosis is easier in a group situation than in a single animal. Kennel cough is usually suspected if a cough matching the above description is observed. Laboratory analysis of a sample of the nasal secretions can confirm which viruses or bacteria are responsible, thus indicating which treatment will be most effective. In isolated cases, other possible causes of the same symptoms should be investigated before concluding that the disease is kennel cough.


The only effective medical treatment is an antibiotic in aerosol form.


The value of laboratory analysis prior to implementing treatment is limited. The only effective medical treatment is an antibiotic in aerosol form. If treatment is administered within 48 hours of the onset of the first symptoms, the injection of a serum specific to the principal pathogens may be effective. To make the dog more comfortable, antitussive (cough-relieving) agents are also given.

The risk of kennel cough can be reduced by taking proper sanitary measures. The kennel layout is important: an outdoor area and an area with a constant temperature should be available to the dogs. The kennel should be easy to clean and disinfect. A quarantine period allows the kennel owner to determine a dog’s state of health before introducing it into a group, and vaccinations can be administered. A number of vaccines are available, although their effectiveness varies.

© Diffomédia/Royal_Canin
© Rivière

Infectious canine hepatitis

Also called Rubarth’s disease, infectious canine hepatitis (ICH) is an infectious disease specific to carnivores and is caused by a virus that was isolated in dogs in 1933. The disease was essentially encountered in Northern and Central Europe and the U.S.A., affecting mostly young dogs between 3 and 12 months of age, and occasionally adult dogs as well. It is now thought to have been almost completely eradicated.

The disease is caused by canine adenovirus 1 (CAV1), which can live for about 10 days in the environment, but is destroyed by heat and ultraviolet radiation. It has peracute, acute and subacute forms.

The peracute (very severe) form affects puppies, which die within a few hours without displaying any particular symptoms. The acute form comprises an invasion phase during which the dog is apathetic and has a fever for about 48 hours; and a clinical phase with the onset of gastrointestinal symptoms (diarrhoea, vomiting, gastroenteritis, anorexia and increased water intake). In addition, some of the lymph nodes are swollen and ocular symptoms such as conjunctivitis and corneal clouding (“blue eye”) are seen. The dog usually recovers in 6 to 10 days. More rarely, the disease leads to a coma and then death.

The subacute form has essentially the same symptoms, but they are less severe than in the acute form. The dog recovers within 3 or 4 weeks.

The prognosis is usually good, except in the peracute form. However, in some cases, corneal clouding may persist.

Infection results from contact with an infected dog, or by indirect contact (contact with contaminated objects or food). Nursing bitches can also transmit the virus to their puppies, which then develop the peracute form of the disease. The virus primarily enters the body via the gastrointestinal tract, but also via the respiratory tract. The disease is specific to dogs and foxes; the latter can spread the disease through the environment by the excretion of infected faeces or shedding contaminated blood. The urine of affected animals remains infectious for several months after clinical recovery.


Infection results from contact with an infected dog, or by indirect contact with contaminated objects or food.


Once in the body, the virus multiplies in the tonsils and various ganglia (nerve centres), then it may or may not spread. The fact that it can remain localized in certain areas explains why so many cases remain undetected. In the third phase of the disease, the viral particles multiply in targeted organs (the liver, kidneys, gastrointestinal tract and eyes), giving rise to the symptoms outlined above.

Treatment for infectious canine hepatitis involves the administration of a specific serum, which is effective when administered during the first 48 hours of the infection. This is followed by symptomatic treatment for the vomiting, diarrhoea and corneal clouding. Prevention involves isolating new arrivals and blood testing to look for antibodies against the virus. Vaccines are available; these contain CAV2, which is related to CAV1, but does not cause infectious hepatitis. This disease has almost disappeared now thanks to routine vaccination.

© Diffomédia/Royal_Canin


Distemper is a highly contagious disease which affects dogs and wild carnivores. It is caused by a virus from the Paramyxoviridæfamily. It has become rare since 1960, i.e. since the implementation of routine vaccination programmes. However since the beginning of the 21st century it has tended to re-emerge regularly in the form of localised epizootic outbreaks in certain regions. Distemper affects dogs of all ages; sensitivity to the infection varies from one individual to another. Dogs usually become infected by direct contact, inhaling the virus, which enters through the respiratory tract. Once in the body, the virus multiplies in the tonsils and bronchi before spreading throughout the body over a period of about 8 days. From this point, the disease can develop in three different ways. Half of all infected dogs develop a sufficient immune response and the virus disappears. These dogs recover after displaying only a few mild symptoms. In other dogs, however, the immune response is inadequate. These dogs have the characteristic symptoms of the disease. Finally, in a minority of dogs, apparent recovery takes place, but the dogs display neurological symptoms a month later.

The most classical form of this disease develops as follows. The incubation period lasts 3 to 7 days, during which time the dog displays no symptoms. The virus then spreads through the dog’s body provoking pyrexia (fever) of up to 40°C, a yellow discharge from the eyes and nose and sometimes small pustules on the abdomen. This stage lasts 2 to 3 days and is followed by a stage in which the dog seems to return to normal, except for persistent conjunctivitis. Next comes the clinical phase, during which the majority of the classic symptoms of canine distemper are seen. The body temperature remains high (about 39.5°C), the mucous membranes are inflamed, a discharge appears from the nose and eyes, the dog has diarrhoea and coughing betrays the presence of tracheobronchitis.

The virus may be localized in various sites provoking rhinitis, conjunctivitis, bronchial pneumonia (revealed by coughing and respiratory problems), gastroenteritis (causing diarrhoea and vomiting) and keratitis (inflammation of the cornea) with ulceration, which are all symptomatic of complications due to the presence of bacteria. Later on in the disease, the reaction of the immune system leads to the development of neurological symptoms. If the symptoms appear rapidly, paralysis, seizures, involuntary muscle contractions and incoordination may be observed. When the symptoms take longer to appear (up to several months) the dog still displays lack of coordination and this ataxia progressively develops into paralysis. Involuntary muscle contractions and visual problems also occur. There are various modes of progression including neurological, respiratory or dental.

Atypical forms of the disease also exist. One form affects the skin and nerves, causing thickening of the nose and footpads, nasal and ocular discharge and persistent fever. This form progresses slowly. After a few weeks, encephalitis appears and leads to death. Another form of encephalitis (old-dog encephalitis) can affect old dogs, as the name implies.


At least four of the following six criteria must be met before a diagnosis of distemper can be confirmed: nasal and ocular discharge, gastrointestinal symptoms, neurological symptoms and persistent fever, observed in a young dog. Laboratory tests will confirm the clinical diagnosis.

The disease is transmitted by direct contact with infected animals. The virus is usually inhaled and all body secretions contain viral particles. Treatment includes the administration of high doses of a specific serum, and a more general approach to combat secondary infections and relieve gastrointestinal and respiratory symptoms. Prevention is the most effective way to protect a dog against this disease. In large populations of dogs, any new arrivals should be quarantined and the facilities disinfected regularly. Vaccines are available and can be used from eight weeks of age. Dogs should be immunized as soon as possible.

Distemper can also be transmitted to seals; this has led to legislation that forbids the introduction of dogs into the Antarctic in order to protect these endangered wild animals.

© Callaloo Canis/Fotolia


This infectious disease, which can be prevented by vaccination, is caused by a heat-sensitive rhabdovirus which is inactivated by visible or ultraviolet light. It is preserved by cold. The rabies virus has a very marked affinity for nerve tissues. The virus is usually transmitted to dogs through a wound (bite, scratch, etc.) and multiplies locally. After multiplying in the muscle, the virus spreads through the body and enters the nerves. The symptoms of infection with the rabies virus are neurological and always result in the death of the dog. Several possible outcomes are possible following contact with the virus. Once the dog has been infected, the disease may take many courses. Infection may be asymptomatic. Very rare cases of contact with the virus without subsequent development of the disease have been reported; nevertheless, rabies is considered in both man and in the dog as being a fatal disease in 100 percent of cases.

Rabies infection passes through several phases: the incubation period, which last fifteen to sixty days on average, after which the dogs excretes the virus in its saliva - on average for three to ten days. Then the symptoms appear and the dog dies after a short period of evolution (between two and ten days). The symptoms can be classified into two categories, referred to as furious rabies and dumb or paralytic rabies.

During the first phase of the evolution of the disease, the dog simply presents with a change of character. It becomes worried and is constantly active. It looks for somewhere quiet to rest; this is followed by periods of apathy and excitation. The general status of the dog does not seem to be of particular concern.

The disease then progresses and leads to intense agitation along with generalised disorders and notable difficulty in chewing food. The dog then becomes furious and attacks everything in its path. Finally it becomes progressively paralysed and inevitably dies within 4 to 5 days on average.

The other clinical form is known as dumb or paralytic rabies, as the first symptoms to be seen are a paralysis of the jaws. The first phase of this form is also solely comprised of depression. Paralysis of the head region makes it impossible for the dog to feed itself, and the dog does not try to bite. This paralysis then extends to the rest of the body and leads to the death of the dog within two to three days.

Animals which present a danger to man are those in the final phase of incubation, when the virus is excreted in the saliva, as well as animals showing clinical signs of the disease. Numerous tissues and organs represent a source of the rabies virus. Some of these enclose the virus whilst staying in the body, whilst others are responsible for the excretion of the virus and are therefore dangerous for other dogs. This principally involves the saliva. The viral concentration is particularly high in the saliva, which explains why bite wounds are so dangerous for other animals and humans. The bodies of animals which have succumbed to rabies are also dangerous as the virus is very resistant in the external environment. The contagion is essentially linked to bites, but not all bites are contagious.

© Diffomédia/Royal_Canin

Everything depends on the depth of the bite wound as well as the region bitten (areas with a high nerve supply are more dangerous). Other modes of contamination exist, although their importance is lower in comparison to bite wounds. Contact with the mucous membranes can cause contamination when there are lesions which may be difficult to see. If the saliva of a rabid animal has come into contact with an object, these can also be a source of contamination. A few rare cases of contamination via ingestion or inhalation have also been reported, as well as transmission from mother to pups.

The clinical diagnosis of rabies is very difficult to establish, and in fact only a brain biopsy performed at autopsy means that a definitive diagnosis of rabies in the dog can be made. Rabies should be suspected when a dog shows a change in behaviour or displays other characteristic symptoms, particularly in areas where rabies is still endemic. The dog’s lifestyle may also provide an indication as to the likelihood of it coming into contact with an infected animal (fox, cat, another dog, etc.). There is no treatment for rabies, which is almost always fatal.

To keep dogs and other domestic carnivores from becoming infected, preventative measures must be implemented. Firstly, animals from countries which are not rabies-free should not be allowed to travel to other countries, as they may carry the rabies virus with them. Measures for excluding such animals can include denial of entry, requirement for a certificate of vaccination and good health, and quarantine. Secondly, wild animals, particularly foxes, are known carriers of the rabies virus: vaccination programmes have therefore been implemented in wild animals.

© Diffomédia/Royal_Canin

In the last few years, quarantine regulations have been relaxed, allowing the passage of animals between rabies-free countries on the condition that these animals have been correctly vaccinated prior to travel with proof of their immune status via blood testing. This laboratory proof of the dog’s vaccination status enables the dog to travel to rabies-free countries. The UK’s “Pet Travel Scheme” (PETS) is one example.

Individual precautions can be taken to prevent infection between dogs. Dogs which bite and which are suspected of carrying rabies are placed under medical surveillance. In France, suspicious cases are classified into one of several different legal categories. Clinical suspects are animals which display symptoms typical of rabies. Biting suspects are dogs which have bitten a person or another animal for no apparent reason, in an area where rabies is endemic. There is also a category of non-suspect biting dogs which have bitten for no apparent reason, in a rabies-free area.


The best way to protect a dog against rabies is to vaccinate it.


“Clinical suspects” are placed under close watch, in a veterinary hospital, until the diagnosis of rabies can be confirmed. Animal’s that bite are placed under so-called “biter” surveillance, which involves a two-week period during which time the dog is examined three times by the vet. The first visit is within 24 hours of the bite, the second on the 7th day thereafter, and the third 15 days after the bite. During each of these visits, if the dog is in good health, the vet draws up a certificate stating that on the date of the examination, the dog had no symptoms of rabies. This legal procedure varies from country to country, but the principle of monitoring remains the same. It is forbidden to give a booster shot of rabies vaccine during this period. Of course, the dog may remain with its owner. If at any time during this period the dog shows symptoms of rabies, it is immediately taken to the vet and placed under veterinary surveillance, as for a clinical suspect. The “biting dog” surveillance is then considered to be at an end.

The best way to protect a dog against rabies is to vaccinate it. The first vaccination cannot be given until the dog is at least three months old and is in good health. A single inoculation is generally sufficient, although a second one may be advised for a young dog. Booster injections must be given either annually or every 3 years depending on the country, and on the requirements of any country to which it is intended to travel with the dog.

Finally, it is important to remember that rabies can be transmitted to humans through bites or scratches, that a vaccine is also available for humans, and that the disease is also fatal in man if treatment is not provided very early on in the disease. Rabies is a major zoonosis.


Parvovirus infection is a contagious disease which appeared in the U.S.A. and Australia in 1978, and is now found all over the world. It is caused by a member of the parvovirus family which is very resistant in the environment. This disease usually causes haemorrhagic gastroenteritis. Clinical signs appear after an incubation period of three to four days. The dog is initially prostrate and anorexic. It will then start to vomit, which is rapidly followed by bloody diarrhoea. After four to five days, the stools become pinkish-grey in appearance, which is characteristic of this disease and the dog has a distinctive odour.


In the peracute (very severe) form of this disease, the dog becomes extremely dehydrated and dies within two or three days. In the acute form, the reduction in blood volume caused by the diarrhoea and vomiting and the secondary bacterial infections result in death within five to six days. If it has not succumbed by the fifth day, the dog usually recovers.

This disease is particularly dangerous for young puppies aged six to twelve weeks, i.e. when the protection conferred by their mother’s antibodies wears off. There is also a rare myocardial form of the disease which only affects one- to two-month old puppies who have not received any maternal immunity. The disease is usually fatal after a short period of respiratory distress. Surviving puppies usually suffer from cardiac problems. It is also possible for some dogs to be infected without showing any symptoms.

Dogs can be infected directly through contact with an infected dog. Indirect infection is also possible via contact with objects that have been soiled with contaminated faeces.

The virus enters through the nose or mouth, then multiplies in the ganglia (nerve centres) before spreading through the body via the blood stream between the second and fifth day. Once the virus has been disseminated in the blood, it multiplies in the gastrointestinal tract, destroying the cell-lining of the intestines and causing an intestinal infection. The virus is primarily excreted in the faeces and to a lesser extent in the urine and saliva. Young and old dogs are more susceptible to infection.

Diagnosis is more difficult in a single animal, but is fairly easy within a population. In group situations, the disease is highly contagious, affecting dogs aged between six and twelve weeks of age with a 50% mortality rate. Some animals suffer from haemorrhagic gastroenteritis. Those that live beyond the 5th day usually make a rapid recovery. Laboratory examination can confirm the diagnosis, either by detecting the virus in the stools, or by identifying antibodies specific for the disease in the blood.

These antibodies can be detected as soon as diarrhoea appears. In both cases, it is important to differentiate between the “wild” virus that causes the disease and the strain used for vaccination. Symptomatic treatment can be given for about 4 days to stop the vomiting and diarrhoea and rehydrate the dog; secondary bacterial infections are prevented from entering through the lesions caused by the multiplication of the viruses in the cells of the gastrointestinal tract.

In breeding kennels, preventive measures are strongly recommended. Contaminated areas should be disinfected with bleach and affected animals should be quarantined (although this is made less effective by the fact that the virus is so resistant in the outside environment, particularly on the coat). Puppies can be vaccinated against parvovirus from six weeks of age.

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