Canine Viral Diseases – An Overview
Dogs of different breeds are always a subject of attraction for human beings. With this attraction the interest of rearing of dogs particularly in metro cities and urban areas are significantly increasing. A segment of society keeps them as a status symbol and during this they remain very near to owners and even share the bedding and rooms. In middle class and lower class dogs are kept in close vicinity due to lack of space. Thus the health of dogs, kept as pet, is of major concerns. Dogs may be affected by bacterial, viral and mycotic pathogens which adversely affect their health, physical status and appearance. Out of these viral infections are of utmost importance as viral diseases:
- Mostly acute or per-acute in nature.
- Have high morbidity and mortality rate.
- Contagious in nature.
- Persistence is common.
- Some are zoonotic in nature.
- Lack of effective and accurate treatment.
- High cost of antiviral therapy.
Keeping all these facts in view present article is to make dog owners aware regarding viral diseases, their etiology, route and mode of transmission, clinical signs and measures to be adopted for prevention and control of diseases. The major viral diseases of dogs are:
- Canine parvo virus
- Canine adeno virus
- Canine distemper
- Canine para influenza
- Canine rabies
Canine parvo virus -2 causes parvoviral enteritis within one to two weeks after infection. Some breeds of dogs like Rottweilers, German Shepherds, Doberman Pinschers and Labrador Retrievers are more susceptible for this infection.CPV-2 is very resistant to environment conditions and disinfectants and can survive several months in contaminated areas as it can withstand high temperatures and wide ranges of pH. The virus is transmitted via direct contact with an infected dog, or via oral contact with infected feces. The virus starts to be shed in the feces within three to four days of infection and up to three weeks following infection. Transplacental transmission to puppies through placenta from infected bitches is also reported.
After ingestion, virus initially replicates in pharyngeal lymphoid tissues and then spread to rapidly diving cells in the body through haematogenous route leading to destruction of the intestinal crypts within 3 days of infection. It further tends to collapse of intestinal villus, diarrhoea, bleeding and vomiting. Young pups that are infected prior to birth, or before they are eight weeks old can develop myocarditis which causes either acute heart failure or scarring of the heart muscle, causing insufficient heart function.
Depression, lethargy, anorexia and vomiting are initial signs with the onset of mucous and blood tinged diarrhoea within 24 to 48 hours after the onset of illness. Severely affected dogs may show septic shock. Recovered animals develop lifelong immunity.
Treatment and Prevention
Use of disinfectant, separation of infected animals and use of fluid therapy along with symptomatic treatments are commonly referred to save the life of pet. Immunization is the best way to prevent the occurrence of disease. Both live attenuated and inactivated vaccines are commercially available. Live attenuated (modified) virus vaccine is recommended over inactivated virus as it produces better immunity of longer duration. Vaccination in pups is recommended at the age of 5 to 8 weeks of age with booster vaccination at 16 to 20 weeks of age. Then annual re-vaccination is recommended.
Infectious tracheobronchitis (kennel cough) is an acute inflammation of the upper airways that can progress to fatal pneumonia in puppies, or to chronic bronchitis in older dogs. The disease is highly contagious and spreads quickly among dogs that are housed together (For example, kennels and Veterinary clinics). CAV-2, a member of the Adenoviridae virus implicated as a cause of infectious diseases of the respiratory tract, is spread mainly via direct (nose-to-nose) and indirect contact with nasal secretions of infected dogs. Mostly infection occours in the combination of canine parainfluenza, canine distemper virus and Bordatella bronchiseptica. Stress and environmental extremes in ventilation, humidity and temperature can increase susceptibility and severity of disease.
Disease starts with harsh, dry cough of productive or non-productive type. Coughing is increased with excitement and exercise. Dogs with non-complicated infections commonly do not show signs of a systemic illness. However, serious respiratory complications can arise in the presence of secondary invaders. Complicated infections may display clinical signs such as fever, pus in nasal discharge, depression, anorexia and productive coughing.
Treatment and Prevention
Proper nutrition good hygienic measures and limited exposure to stray and other suspected diseased dogs may prevent the infection.
Immunization of dogs with a modified live virus vaccine is effective. Puppies should receive their initial vaccinations when they are 6 to 8 weeks old. The vaccine should be administered 2 more times at 2 to 4 week intervals until the pups are 14 to 16 weeks old. Annual revaccination is recommended.
Canine distemper virus is a paramyxovirus .It is responsible for a highly contagious systemic viral disease in dogs. The virus affects canids as well as many some other species. The virus is sensitive to environmental conditions, and is found in respiratory secretions, fecal material and urine from infected animals even few months after recovery. Contact with these infected materials can result in infection of the naïve animal. The virus first grows in the respiratory lymphoid tissue and then during viremia passes to all lymph tissue, and to the epithelium of the respiratory, urinary and gastrointestinal tracts including central nervous system (brain and spinal cord) and the optic nerves.
Onset of the disease shows transient fever, anorexia and listless along with leucopenia. Some time initial stage passes unnoticed and followed by second stage of fever which generally lasted for seven days. With the advancement of disease clinical signs like watery discharge from the nasal cavity and congestion and discharge of pus from the eyes, coughing, diarrhea and vomiting are also recorded.
Hyperkeratosis of nasal plane and foot pads and neurological disorders as paresis, paralysis or ataxia of the hind limbs are observed. Some animals also experience twitching of face and leg muscles along with convulsions that are characterized by salivation and chewing-motions. The seizures increase in both frequency and severity as time progresses with the involuntary urination and defecation during the seizures.
Treatment and Prevention
Maternal antibodies received from colostrum of immunized dam may protect puppies during the early stage of life. These maternal antibodies interfere in vaccination. Therefore, pups are vaccinated at six weeks of age, and again at two to four week intervals with annual revaccination.
Canine Parainfluenza Virus
Canine Parainfluenza Virus (CPiV) is a single-stranded RNA virus of the virus family Paramyxoviridae. Canine parainfluenza virus (CPiV) typically causes mild respiratory tract infections but the presence of secondary invaders like canine adeno virus, bordatella bronchiseptica, canne herpes virus, mycoplasmas and sometime mycotic infection result in canine infectious tracheobronchitis (kennel cough). Kennel cough is an acute inflammation of the upper respiratory tract that can progress to fatal pneumonia in puppies, or to chronic bronchitis in older dogs. The disease is highly contagious and spreads quickly in closely associated dogs. The virus is transmitted via contact with the nasal secretions of infected dogs. CPiV infection is restricted to the upper respiratory tract and causes damage to the epithelium lining the trachea (windpipe). This allows for secondary infection by other pathogens, which can complicate the infection and result in more serious disease leading to tracheobronchitis, laryngitis and pneumonia. Stress and environmental extremes in ventilation, humidity and temperature increase susceptibility to disease and severity of disease.
Dogs infected with disease show dry coughing and nasal discharge. Dogs may retch, and possibly produce mucous. The prognosis for recovery from infection is good if the dog receives appropriate treatment upon onset of disease.
Treatment and Prevention
Only way to prevent the disease is immunization. Dogs should be immunized with a modified live virus vaccine. Young pups should receive their first vaccination with at the age of 6 to 8 weeks old, with subsequent vaccinations every 3 to 4 weeks until they are 12 to 14 weeks old. Annual re-vaccination is recommended.
Rabies is fatal acute disease of canines and characterized by encephalomyelitis. The causing agent of Rabies is caused Lyssa virus belonging to Rhabdoviridae. Wild animals act as reservoir and for sylvatic form of rabies the bats are main source of infection. The rabies is mainly transmitted through the saliva of an infected animal, almost always via penetrating bite wounds. Rarely, the virus has been spread from the saliva, salivary glands or brain through open wounds or intact mucous membranes. The viruses are found in saliva shortly before or immediately with the onset of clinical signs. Aerosol spread of the virus is incredibly rare. The incubation period of rabies is highly variable depending upon the site of wound, depth of bite, no. of viruses in bite and many other factors but generally it is quite long from 21-80 days to years. At the site of bite virus may remain for a considerable length of time. Then virus moves through centripetally peripheral nerves to the spinal cord and from the spinal cord to the brain. From brain, the virus descends centrifugally through peripheral nerves and reachs the salivary glands. Once the virus is established in the salivary glands, it can be transmitted via the saliva, and will be detectable in the brain.
The clinical signs of rabies are not always definitive and are mostly related with central nervous system (CNS) disturbance. Sudden and unexplainable behavioral changes like anorexia, irritability, anxiety, apprehension, hyper excitability, unexplained aggressiveness, loss of coordination and a rapid onset of a progressive paralysis with animals seeking out solitude. In general there are three clinical phases of rabies:
- Prodromal Period
- Excitative Period
- Paralytic/End stage
The prodromal phase is characterized by vague CNS signs and typically lasts 1-3 days. These signs rapidly intensify in the Excitative period with the apparent clinical signs. Once clinical signs are evident the disease is invariably fatal. With the progression into the onset of incoordination and paralysis as the terminal or end stage. Usually these phases do not occur in all affected animals as sometime affected animals die acutely with minimal or without clinical signs.
In some infected animals, aggression becomes incredibly pronounced.
“Furious Form” is characterized by pronounced aggression and rare evidence of early paralysis. Excessive alertness, anxiety, dilation of pupil and loss of fear along with attacking tendency on slight provocation are common signs of this stage. In “Paralytic Form” form of the disease, dropped bottom jaw with profuse salivation and inability in swallowing due to the paralysis of throat and masticatory muscles are observed. The rapid spread of paralysis throughout the body usually bring animal in comatose state and die within a few hours.
Suspected animals for bite of rabid animals must be brought to a veterinarian immediately as early treatment is essential. The rabies diagnosis is difficult as it can be confirmed only by testing the brain in a diagnostic laboratory.
Treatment and Prevention
There is no treatment of rabies after the onset of clinical signs. Although the infection. Only way to protect domestic animals is vaccination. Vaccination is recommended every three years, after an initial series of two vaccines, one year apart. Rabies can be spread from infected wild or domestic animals to human beings.
The viral diseases are mostly deadly and incurable. Thus prevention of viral diseases is most important. The control and prevention of viral diseases in pet animals require:
- Better management practices.
- Strict hygienic measures.
- Awareness regarding the diseases.
- Scheduled vaccination.