Content
Adenovirus infection of calves (CAVI) 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. This only means that the causative agent of the disease has been identified for the first time in the United States. Later, the adenovirus was 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: adenoviral pneumoenteritis and adenoviral pneumonia of calves. Diseases are caused by DNA-containing viruses that integrate into the cells of the body. In total, 62 strains of adenoviruses have been counted so far. They affect not only animals, but also people. Nine different strains have been isolated from cattle.
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 bovine adenoviruses are highly resistant in 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 using a solution of formaldehyde 0.3% and ethyl alcohol with a strength of 96%.
Viruses of all strains are very resistant to thermal influences. At a temperature of 56 °C they die only after an hour. The viruses are kept at 41°C for a week. This 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, a high percentage of deaths occurs in very young calves.
Viruses can withstand freezing and thawing up to 3 times without losing activity. If an outbreak of AVI occurs in the fall, then one cannot expect that the pathogen will be inactivated due to cold in winter. You can expect the disease to return in the spring.
Sources of infection
The sources of infection are animals that have recovered from the disease or are latently ill. This is one of the reasons why young animals cannot be kept together with adult animals. In adult cows, adenovirus infection is asymptomatic, but they can infect calves.
Transmission of the virus occurs in several ways:
- airborne;
- when eating 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 feces of an adult cow. In this way he receives the microflora he needs. If a cow is latently sick with an adenoviral infection, infection is inevitable.
All cows with leukemia were also infected with adenovirus. Upon penetration of the mucous membrane, the virus invades 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 infected with adenovirus, calves can develop three forms of the disease:
- intestinal;
- pulmonary;
- mixed.
Most often, the disease begins with one of the forms and quickly develops into a mixed form.
Symptoms of adenovirus infection:
- temperature up to 41.5 °C;
- cough;
- diarrhea;
- tympany;
- colic;
- mucus discharge from the eyes and nose;
- decreased appetite or refusal to feed.
Initially, the discharge from the nose and eyes is clear, but quickly becomes mucopurulent or purulent.
In calves under 10 days of age that receive antibodies with their mother's colostrum, adenoviral infection does not manifest itself clinically. 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.
The acute form occurs in calves aged 2-3 weeks. As a rule, this is the intestinal form of adenoviral pneumoenteritis. Characterized by severe diarrhea. Feces often contain blood and mucus. Severe diarrhea causes the body to become dehydrated. With this form, the death rate of calves can reach 50-60% in the first 3 days of the disease. Calves die not because of the virus itself, but because of dehydration. In fact, this form of adenoviral infection is an analogue of cholera in humans. You can save the calf if you have time to restore its water balance.
In older calves, a chronic form of adenoviral infection often occurs.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 carries the virus 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 of the diseases are similar, there are also differences. But in order to catch them, you need to know well the signs of disease and the habits of calves. Treatment should begin before the laboratory tests arrive.
Parainfluenza-3
Also known as bovine parainfluenza and transport fever. Has 4 types of flow. Hyperacute is usually observed in calves up to 6 months: severe depression, coma, death on the first day. This form has nothing in common 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 exudate from the nose;
- lacrimation;
- Outwardly, a return to a healthy state occurs in 6-14 days.
In the subacute course, the symptoms are similar, but not as pronounced. They disappear within 7-10 days. In acute and subacute cases, parainfluenza can easily be confused with AVI in cattle.Since the symptoms disappear, the owners do not treat the calves and lead to a chronic course, which is also similar to an adenovirus infection: retarded growth and development.
Pasteurellosis
Symptoms of pasteurellosis may also include:
- diarrhea;
- refusal of food;
- nasal discharge;
- cough.
But if, with an adenovirus infection, small calves die on the 3rd day, and older calves externally 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
This infection is similar to adenovirus due to:
- high body temperature (41 °C);
- cough;
- serous nasal discharge;
- 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 of food;
- diarrhea;
- respiratory:
- temperature rise 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 in the encephalitic form.
Viral diarrhea
There are few signs similar to AVI cattle, but they exist:
- temperature 42 °C;
- serous, later mucopurulent discharge from the nose;
- refusal of food;
- cough;
- diarrhea.
Treatment, as with AVI, is symptomatic.
Infectious rhinotracheitis
Similar signs:
- temperature 41.5-42 °C;
- cough;
- copious nasal discharge;
- refusal of food.
Most animals recover on their own after 2 weeks.
Changes
When autopsying a corpse, 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 mucosal cells, in common parlance sputum;
- a collection of white blood cells around small blood vessels in the lungs.
After a long illness, changes caused by secondary infection are also found in the lungs.
Treatment
Since viruses are part of RNA, they cannot be treated. The body must cope on its own. Adenoviral infection of calves in this case is no exception. There is no cure for the disease. You can only carry out a symptomatic auxiliary course to make the calf’s life easier:
- eye wash;
- inhalations to make breathing easier;
- drinking decoctions that stop diarrhea;
- use of antipyretics;
- broad-spectrum antibiotics to prevent secondary infection.
But the virus itself remains with the cow for its entire life. Since adult cattle are asymptomatic, the dam can transmit the adenovirus to the calf.
To help the body fight the virus, hyperimmune serum and serum from convalescent animals containing antibodies to the adenovirus are used.
Forecast
Adenoviruses affect not only animals, but also people. Moreover, 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 high temperatures well. They stop eating and quickly die. The picture is worsened by diarrhea, which dehydrates the calf. These reasons explain the high mortality rate 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. A recovered animal develops antibodies in its 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 “suspected” of disrupting spermatogenesis.
Preventive measures
Specific prevention is still under development. For now, general sanitary and veterinary principles apply:
- kept in good conditions;
- maintaining hygiene;
- quarantine of newly arrived animals;
- ban on the import of livestock from farms unaffected by adenovirus.
Due to the large number of virus strains, immunoprophylaxis for AVI is less developed than for other viral diseases. This is due not only to the large number of strains, but also to the hidden course of the disease in adult cows.
The search for means of protection against adenoviral infection today is carried out in 2 directions:
- passive protection using immune serums;
- 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 using immune sera is not practical.In addition, such protection is difficult to apply in mass quantities.
Vaccines have proven to be more reliable and shelf-stable. In the CIS, mono-vaccines are used based on strains of two groups of adenoviruses and a bivalent vaccine, which is also used against cow pasteurellosis. Queens are vaccinated with the monovaccine twice at 7-8 months of pregnancy. The born calf acquires resistance to AVI through the mother's colostrum. Immunity to adenovirus lasts for 73-78 days. Afterwards, the calves are vaccinated separately from the uterus. In order for the calf to begin to produce its own antibodies by the time the “borrowed” immunity ends, it is vaccinated for the first time between the 10th and 36th day of life. Repeated vaccination is done 2 weeks after the first.
Conclusion
Adenoviral infection of calves, if precautions are not followed, can cost the farmer his entire newly born livestock. Although this will not affect the quantity of dairy products, due to insufficient knowledge of the virus, the veterinary service may impose a ban on the sale of milk.
