List of two major diseases caused due to virus in animals:- 1. Canine or Dog Distemper 2. African Horse Sickness.
Disease # 1. Canine or Dog Distemper:
Definition:
Distemper in dogs is an acute infective disease caused by a virus and is nearly always complicated by numerous secondary invaders, e.g. Bordetella, Salmonella enteriditis, Brucella bronchisepticus, Streptococcus cerebritis and various Staphylococci, and is characterised by four different types of symptoms , e.g., Pulmonary, Gastro-intestinal, Nervous and Exanthematous.
Incidence:
Distemper is a extremely common and universally distributed in dogs and is more prevalent in cities than in the open countries.
Animals susceptible:
Dogs and other members of canine species such as fox, wolf, ferret, mink etc, particularly young animals ageing from 3 weeks to 1 year, which diminishes with the increase in age.
Incubation period:
3 to 21 days.
A natural attack confers a strong and lasting immunity.
Pathogenesis:
At the onset, the virus causes a septicaemia, characterised by sharp rise in temperature, which, in itself may sometimes be fatal, but this is usually followed by the effects of secondary invaders which produce the symptoms of anyone or more of the four types mentioned.
Modes of infection:
Ingestion of contaminated food and water, inhalation of air in the neighbourhood of an infected animal and by droplet infection. It has been found experimentally that the virus can be carried about 2 ft. by air in a closed room and about 12 metres by the wind in the open.
Postmortem lesions:
The lesions are chiefly those caused by secondary invaders and vary in accordance with the symptoms, which, however, are not diagnostic.
The lesions usually seen in different forms are as follows:
(a) Pulmonary:
Ecchymosis over most of the visceral pleura, purulent plugs in bronchioles, areas of atelectasis (solidification) in the lungs and fibrinous pleurisy.
(b) Gastro-intestinal:
Catarrhal gastroenteritis and occasional ulceration of the gastric or intestinal mucosa.
(c) Nervous:
Macroscopically visible haeamorrhages in Pia-arachnoid, infiltration of the glia cells, vacuolation of superficial cells of the cerebral cortex and diffused encephalomyelitis.
(d) Miscellaneous:
Inflammation of thoracic and mesenteric lymph glands, petechial myocarditis, parenchymatous degeneration of the liver and kidneys.
Symptoms:
Initial symptoms:
In peracute or septicaemic form, commences with a very high rise of temperature — 106° to 107°F and marked constitutional, e.g., great depression, fatigue, total a loss of appetite etc. The temperature in the course of several hours drops to normal and later to subnormal, followed by coma and death in 1 to 3 days.
The acute form also begins with a rise of temperature — 103° to 106°F which remains elevated for several days or weeks. Some cases show marked variations in temperature, beginning with a high temperature, which in a few days drops to normal or in some cases to subnormal, where it remains until either recovery or death. In some cases, the fever, may be of a remittent type.
The animal becomes dull, depressed and does not respond to master’s call. The hair becomes rough, soon loses its gloss and the animal shows an extremely dejected appearance. The nose becomes hot and dry and there is violent sneezing followed after one or more days with pronounced of the respective four forms of the disease. There may be occasional fits at the onset.
(a) Pulmonary type:
These may be occasional fits at the onset, spasmodic cough, sometimes resulting in vomiting and dyspnoea. The discharge from the nostrils increases and may be stained with streaks of blood. On auscultation over the areas of the lungs, areas of bronchial breathing, dry or moist rales or absence of respiratory sounds are revealed. Broncho-pneumonia is one of major complications of the disease.
(b) Digestive symptoms:
Gastro-enteritis:
These are nearly always associated with all the other three types and begin early as shown by anorexia, vomiting, constipation followed by diarrhoea, thirst, coating and ulceration of the tongue, buccal mucosa and gums. These lesions of the mouth and with the gas regurgitated from the stomach, give rise to extremely bad odour perceptible when the mouth of the dog is opened for examination. There is coppery discolouration of the tongue. Sometimes worms are expelled spontaneously during bowel complications. This diarrhoea causes rapid emaciation and great weakness.
(c) Nervous symptoms:
These may begin with the after initial symptoms or occur as late as 5 or 6th week. These usually comprise of chorea like spasms of any muscles — specially the muscle controlling the lips, alae nasi, cheeks, ear fore or hind limbs.
When nervous symptoms develop early in the attack, they are often manifested by epileptic form convulsions. The animal falls down, screams of yelps, foams at the mouth, rolls on to its side and become unconscious. There may be involuntary evacuation of urine and faeces due to relaxation of-the sphincters of bladder and rectum.
In very acute case, the epileptic form convulsion may terminate in death in a few hours. In less acute cases, paresis develops, which usually begins in the hind limbs and progresses forward. Death occurs when any group of vital muscles is affected by paralysis.
(d) Skin symptoms:
Some cases of distemper, are affected by eruptions of skin, specially of the abdomen. These begin as small papules terminating in pustules which later on, become encrusted and emit a repulsive odour. In rare cases, the pads of the feet become thickened and swollen, occasionally to such an extent that they make a tapping sound on the floor when the dog walks and thus, it is called “Hard pad disease”. Inflammation of the kidneys, bladder, testes, liver, heart wall may appear during the course of the disease.
The urine in all cases is dark coloured and may contain bile pigments and albumin.
Course:
Peracute case — 1 to 3 days. Other forms — 10 days to 6 weeks.
Diagnosis:
This is usually made from the clinical symptoms or else by means of the complement fixation test, using the dog’s spleen as antigen. Ferrets can be used for inoculation.
Mortality:
This averages 50 per cent. The prognosis is most favourable in the exanthematous form in which 70 per cent may recover. Least favourable when nervous symptoms predominate and in this form, the recovery is only 10 to 15 per cent. An unfavourable sign is sudden rise and rapid fall of temperature (Septicaemia).
Treatment:
There is no specific treatment other than serum for this disease. Even immuned serum, to be of value as a therapeutic agent, must be injected very early in the attack, preferably within 48 to 60 hours after the initial rise of temperature.
Anti-Distemper and Infectious serum to be given intravenously for preference. A small sized dog should have 1ml per formed of body weight. A second dose of serum may be administered within 48 hours if fever has not began to decline. A small sized by should have 10ml, a medium sized one – 20 ml and a large dog – 30 to 40 ml and if necessary, it must be repeated.
The use of Penicillin, Tetracycline, Chloromycetin in conjunction with serum therapy is advocated. Doxicycline is another useful drug. Procaine penicillin with dihydrostreptomycin in proper dosage according to body weight, given intramuscularly every 24 hours for 3 to 5 days in very help in combating secondary infections.
Supportive therapy consisting of intravenous injection of 5 per cent dextrose in normal saline with Vitamin B Complex is of great value in maintaining patient’s fluid balance. Vitamin A and D should be given by administration of a few drops Halibut liver oil. Even combination of Sulpha drugs — i.e. Sulphamethazine, Sulphadiazene and Sulphamerazine in equal parts are quite effective in controlling secondary bacterial infections.
Nervous symptoms should be checked by barbiturates. It necessary, Calmpose may be administered parenterally to prevent fits.
Mild antiseptic solutions may be used to soften any dried ocular secretions and nasal discharges and into antiseptic ophthalmic ointment may be applied to the eyes.
Since nutrition is the major consideration, a mixture of eggs, milk, glucose should be given, which in case of inability to take, must be given with the help of stomach tube, a little at a time but several times daily. Essence of chicken, raw meat juice are good supportive.
N.B.:
Proper elimination must be maintained at all times and nothing should be given to bring on constipation.
Immunity:
Anti-canine distemper serum will create a passive immunity lasting 10 to 14 days. The use of serum is useful whenever a short period of protection is necessary. Small puppies may be given serum every two weeks until active vaccination can be performed.
For Active immunity, many vaccines are available. Combined Vaccines against distemper, virus hepatitis and leptospirosis may be given followed by a booster dose. A measles virus vaccine has been introduced for use in dogs to give protection against distemper. This vaccine can be used in puppies 3 weeks old and upwards and immunity is established in 72 hours and last 5 month at least Distemper — CVH vaccines either contain two live viruses or live distemper and inactivated CVH virus. But this vaccine must be used only in healthy puppies. Several other combined vaccines are now available and may be used according to the directions.
Virus-serum method is also quite effective. First a dose of virus is given and within an hour, the serum is given. If still there is a rise of temperature, then a second dose of serum is given.
Disease # 2. African Horse Sickness:
Definition:
African Horse Sickness is a highly fatal, infectious disease of horses, mules and donkeys. It is caused by a number of strains of a virus spread by insect vectors.
Etiology:
The disease is caused by a viscerotropic arbovirus. A number of antigenic strains of the virus exist and there is evidence of some cross-immunity between strains. Therefore, it is essential in large-scale vaccination programmes to include a number of strains in the vaccine. The vaccine currently in use contains 7 strains and is effective in most areas. It is spread by insects.
Epidemiology:
African Horse Sickness was confined to African continent but since 1959, it spread to Iran, Pakistan, India, Middle East, Turkey, Eastern Mediterranean and Cyprus. It is an enzootic disease in Africa.
Pathogenesis:
It is a disease of vascular endothelium with virus clones affecting endothelium in different organs, resulting in a variety of forms of the disease. The virus is present in the blood stream from the first day of clinical illness and persists for about 30-90 days.
Symptoms:
The incubation in natural infections is about 5-7 days. Three clinical forms of the disease occur, an acute or pulmonary form, a cardiac or sub-acute form and a mild form known as Horse sickness fever. An intermittent fever of 40°-41°C (140°-106°F) is characteristic of all forms.
Acute (Pulmonary) Form:
This is the most common form in acute outbreaks in susceptible animals. Initially there is fever followed by very laboured breathing and severe paroxysms of coughing. There is profuse nasal discharge of yellowish serous fluid and froth. Profuse sweating commences an the horse becomes very weak, develops a staggery gait and becomes recumbent.
At this time, the nasal discharge is usually voluminous. Initially, the appetite is good but later the animal is unable to eat due to laboured breathing. Death follows within a few hours after a total course of 4-5 days. In the few animals which recover severe dyspnea persists for many weeks.
Subacute (Cardiac) Form:
This is the most common in horses in enzootic areas. The incubation period may be longer, up to 3 weeks, and the fever develops more slowly and persists longer than in the acute disease. The most obvious sign is edema in the head region, specially the temporal fossa, the eyelids and the lips and may spread to the chest.
The above symptoms develop when the horse has been febrile for a week. The oral mucosa is bluish in colour. Restlessness and mild abdominal pain are often evident. Auscultation of the heart and lungs reveals evidence of Hydropericardium, Endocarditis and Pulmonary edema. Paralysis of the Oesophagus with inability to swallow and regurgitation of; food and water through the nose is not uncommon. A fatal course may be as long as two weeks.
Horse Sickness Fever Form:
It presents no diagnostic signs and may go unrecognized except that it usually occurs in areas in which the disease in enzootic. The temperature rises to 40.5°C (105°F) over a period of 1-3 days but returns to normal about 3 days later. The appetite is poor, moderate dyspnea and there is slight conjunctivitis.
Treatment:
No treatment has been shown to have any effect on the course of the disease but careful nursing and symptomatic treatment is not without value.
Prophylaxis:
The vaccine currently in use in Middle East and India contains seven strains of attenuated virus and has proved to be very effective. Immunity after vaccination is solid for atleast a year but animal revaccination of all horses, mules and donkeys is recommended.