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Adenovirus infection of calves (AVI bovine) as a disease was discovered in 1959 in the USA. This does not mean that it originated on the North American continent or spread from there throughout the world. It only means that the causative agent of the disease was first identified in the United States. Adenovirus was later identified in European countries and Japan. In the USSR, it was first isolated in Azerbaijan in 1967 and in the Moscow region in 1970.
What is adenovirus infection
Other names for the disease: adenovirus pneumoenteritis and adenovirus pneumonia of calves. Cause disease DNA-containing viruses embedded in the cells of the body. In total, 62 strains of adenoviruses have been counted so far. They affect not only animals, but also people. In cattle, 9 different strains have been isolated.
The virus causes a cold-like illness when it enters the lungs. The intestinal form is characterized by diarrhea. But the mixed form is much more common.
Calves aged 0,5-4 months are most susceptible to AVI. Newborn calves rarely get sick. They are protected by antibodies obtained from colostrum.
All adenoviruses of cattle are highly resistant to the external environment, as well as to disinfectants. They are resistant to the main disinfectants:
- sodium deoxycholate;
- trypsin;
- ether;
- 50% ethyl alcohol;
- saponin.
The virus can be inactivated with a 0,3% formalin solution and 96% ethyl alcohol.
Viruses of all strains are very resistant to thermal effects. At a temperature of 56 ° C, they die only after an hour. 41 ° C viruses withstand for a week. That is how long an adenovirus infection lasts in a calf. But since it is difficult for an animal to withstand a high temperature plus diarrhea, very young calves have a high percentage of deaths.
Viruses are able to withstand freezing and thawing up to 3 times without loss of activity. If the AVI outbreak occurred in autumn, then it is not necessary to expect that the pathogen is inactivated due to the cold in winter. In the spring, you can wait for the return of the disease.
Sources of infection
The sources of infection are animals that have been ill or are ill in a latent form. This is one of the reasons why young animals should not be kept together with adult animals. In adult cows, adenovirus infection is asymptomatic, but they will be able to infect calves.
The transmission of the virus occurs in several ways:
- airborne droplets;
- when eating the feces of a sick animal;
- with direct contact;
- through the conjunctiva of the eyes;
- through contaminated feed, water, bedding or equipment.
It is impossible to prevent a calf from eating the faeces of an adult cow. He thus receives the microflora he needs. If a cow in a latent form is sick with an adenovirus infection, infection is inevitable.
All cows with leukemia were also infected with adenovirus. When penetrating the mucous membrane, the virus enters the cells and begins to multiply. Later, along with the bloodstream, the virus spreads throughout the body, causing already visible manifestations of the disease.
Symptoms and manifestations
The incubation period for adenovirus infection is 4-7 days. When affected by adenovirus, calves can develop three forms of the disease:
- intestinal;
- pulmonary;
- mixed
Most often, the disease begins with one of the forms and quickly flows into a mixed one.
Symptoms of adenovirus infection:
- temperature up to 41,5 °С;
- cough;
- diarrhea;
- tympanum;
- colic;
- discharge of mucus from the eyes and nose;
- loss of appetite or refusal to feed.
The discharge from the nose and eyes is initially clear, but quickly becomes mucopurulent or purulent.
In calves under the age of 10 days, receiving antibodies from the mother’s colostrum, clinically adenoviral infection does not manifest itself. But this does not mean that such calves are healthy. They may also become infected.
Course of the disease
The course of the disease may be;
- sharp;
- chronic;
- latent.
Calves at the age of 2-3 weeks get sick with an acute form. As a rule, it is an intestinal form of adenovirus pneumoenteritis. Characterized by severe diarrhea. Often feces mixed with blood and mucus. Due to severe diarrhea, the body becomes dehydrated. With this form, the death of calves can reach 50-60% during the first 3 days of illness. Calves are dying not because of the virus itself, but because of dehydration. In fact, this form of adenovirus infection is an analogue of cholera in humans. You can save a calf if you have time to restore its water balance.
In older calves, a chronic form of adenovirus infection is common. In this course, calves survive, but lag behind their peers in growth and development. Among calves, adenovirus infection can take on the character of an epizootic.
The latent form is observed in adult cows. It differs in that a sick animal is a virus carrier for a long time and can infect the rest of the livestock, including calves.
Diagnostics
Adenovirus infection is easily confused with other diseases that have the same symptoms:
- parainfluenza-3;
- pasteurellosis;
- respiratory syncytial infection;
- chlamydia;
- viral diarrhea;
- infectious rhinotracheitis.
An accurate diagnosis is made in the laboratory after virological and serological studies and taking into account pathological changes in the body of dead calves.
While the symptoms are similar, there are also differences. But in order to catch them, one must know well the signs of diseases and the habits of calves. Treatment should begin before laboratory tests arrive.
Parainfluenza-3
It’s also bovine parainfluenza and transport fever. Has 4 types of flow. Superacute is usually observed in calves up to 6 months: severe depression, coma, death on the first day. This form has nothing to do with adenovirus infection. The acute form of parainfluenza is most similar to adenovirus:
- temperature 41,6 °C;
- decreased appetite;
- cough and wheezing from the 2nd day of illness;
- mucus and later mucopurulent nasal exudate;
- lacrimation;
- outwardly, the return to a healthy state occurs on the 6-14th day.
In the subacute course, the symptoms are similar, but not so pronounced. Pass for 7-10 days. In acute and subacute course, parainfluenza is easily confused with bovine AVI. Since the symptoms disappear, the owners do not treat the calves and bring them to a chronic course, which is also similar to an adenovirus infection: a lag in growth and development.
Pasteurellosis
Symptoms of pasteurellosis can also be:
- diarrhea;
- refusal to feed;
- nasal discharge;
- cough.
But if, with an adenovirus infection, small calves die on the 3rd day, and the older ones outwardly return to normal after a week, then with pasteurellosis, in the case of a subacute course, death occurs on the 7-8th day.
Respiratory syncytial infection
The similarity with adenovirus infection is given by:
- high body temperature (41 ° C);
- cough;
- serous discharge from the nose;
- developing bronchopneumonia.
But in this case, the prognosis is favorable. The disease in young animals disappears on the 5th day, in adult animals after 10 days. In a pregnant cow, infection can cause abortion.
chlamydia
Chlamydia in cattle can occur in five forms, but there are only three similarities with adenovirus infection:
- intestinal:
- temperature 40-40,5 ° C;
- refusal to feed;
- diarrhea;
- respiratory:
- an increase in temperature to 40-41 ° C with a decrease after 1-2 days to normal;
- serous discharge from the nose, turning into mucopurulent;
- cough;
- conjunctivitis;
- conjunctival:
- keratitis;
- lacrimation;
- conjunctivitis.
Depending on the form, the number of deaths varies from 15% to 100%. But the latter occurs with the encephalitic form.
Viral diarrhea
There are few signs similar to AVI cattle, but they are:
- temperature 42 °C;
- serous, later mucopurulent discharge from the nose;
- refusal to feed;
- cough;
- diarrhea.
Treatment, as with AVI, is symptomatic.
Infectious Rhinotracheitis
Similar signs:
- temperature 41,5-42 ° C;
- cough;
- copious discharge from the nose;
- food refusal.
Most animals recover on their own after 2 weeks.
Path changes
At autopsy, note:
- blood circulation disorders;
- intranuclear inclusions in the cells of internal organs;
- hemorrhagic catarrhal gastroenteritis;
- emphysema;
- bronchopneumonia;
- blockage of the bronchi with necrotic masses, that is, dead cells of the mucous membrane, colloquially sputum;
- accumulation of white blood cells around small blood vessels in the lungs.
After a long illness, the lungs also show changes caused by a secondary infection.
Treatment
Since viruses are part of RNA, they cannot be treated. The body has to cope on its own. Adenovirus infection of calves in this case is no exception. There is no cure for the disease. You can only conduct a symptomatic auxiliary course that makes life easier for the calf:
- eye wash;
- inhalations to make breathing easier;
- drinking decoctions that stop diarrhea;
- the use of antipyretics;
- broad-spectrum antibiotics to prevent secondary infection.
But the virus itself remains with the cow for life. Since adult cattle are asymptomatic, the uterus can transmit adenovirus to the calf.
To help the body in the fight against the virus, hyperimmune serum and serum from convalescent animals containing antibodies to adenovirus are used.
Forecast
Adenoviruses affect not only animals, but also humans. What’s more, scientists believe that some of the virus strains may be common. Adenoviruses belong to the group of acute respiratory viral diseases.
All animals do not tolerate heat well. They stop eating and quickly die. The picture is worsened by diarrhea, dehydrating the body of the calf. These reasons explain the high mortality among small calves that have not yet accumulated “reserves” for a long fight against adenovirus infection.
If these two factors can be avoided, then the further prognosis is favorable. In an ill animal, antibodies are formed in the blood that prevent re-infection of the calf.
The fact has not been proven, but adenovirus is isolated from the testicular tissues of recovered calves. And the virus is under “suspicion” of violating spermatogenesis.
preventive measures
Specific prophylaxis is still under development. While applying the general sanitary and veterinary principles:
- keeping in good conditions;
- hygiene compliance;
- quarantine of newly arrived animals;
- a ban on the import of livestock from farms that are unfavorable for adenovirus.
Due to the large number of strains of the virus, AVI immunoprophylaxis is less developed than for other viral diseases. This is due not only to a large number of strains, but also to the latent course of the disease in adult cows.
Today, the search for means of protection against adenovirus infection is carried out in 2 directions:
- passive protection using immune sera;
- active protection using inactivated or live vaccines.
During the experiments, it turned out that the level of passive protection is very low, since calves with passive antibodies can be infected with adenovirus and transmit it to healthy animals. Protection by means of immune serums is inexpedient. In addition, such protection is difficult to apply in mass quantities.
Vaccines have shown themselves to be more reliable and stable in storage. On the territory of the CIS, monovaccines are used based on strains of two groups of adenoviruses and a bivalent vaccine, which is also used against cow pasteurellosis. The uterus is vaccinated with a monovaccine twice for 7-8 months of pregnancy. The born calf acquires resistance to AVI through the mother’s colostrum. Immunity to adenovirus persists for 73-78 days. After the calves are vaccinated already separately from the uterus. In order for the calf to start producing its own antibodies by the time the “borrowed” immunity ends, it is vaccinated for the first time in the period from 10 to 36 days of life. Re-vaccination is done 2 weeks after the first.
Conclusion
Adenovirus infection of calves, if precautions are not taken, can cost the farmer the entire newly born livestock. Although this will not affect the amount of dairy products, due to insufficient knowledge of the virus, the veterinary service may impose a ban on the sale of milk.
