Content
Intestinal dysfunction is a common symptom of many diseases. Many of these illnesses are not even infectious. Since diarrhea accompanies most infectious diseases, it may seem strange that bovine viral diarrhea is not a symptom, but a separate disease. Moreover, with this disease, intestinal dysfunction is not the main symptom.
What is viral diarrhea
A highly contagious viral disease. Diarrhea is the lesser of the evils that characterize this disease. With viral diarrhea, the mucous surfaces of the intestines, mouth, tongue, and even the nasolabial mirror become inflamed and ulcerated. Conjunctivitis, rhinitis and lameness develop. Fever appears.
The disease causes great economic damage on farms, as sick pregnant cows abort, and lactating cows reduce their milk yield. Viral diarrhea is common throughout the world. Only the strains of the virus may differ.
The causative agent of the disease
The causative agent of this viral disease in cows belongs to the pestivirus genus.At one time it was believed that this type of virus could be transmitted by blood-sucking insects and ticks, but later it was established that cow viral diarrhea is not transmitted this way.
There are 2 genotypes of viruses that cause infectious diarrhea in cows, but they do not differ in virulence. Previously, it was believed that viruses with the BVDV-1 genotype cause milder forms of the disease than BVDV-2. Later studies did not confirm this. The only difference: viruses of the second type are less common in the world.
The diarrhea virus is very resistant to low temperatures in the external environment. At -20°C and below, it can persist for years. In pathanotomy material at - 15 °C it remains for up to 6 months.
The virus is not easy to “finish off” even at positive temperatures. It can withstand + 25 °C for 24 hours without reducing activity. At + 35 °C it remains active for 3 days. The bovine diarrhea virus is inactivated only at + 56 °C and after 35 minutes at this temperature. At the same time, there is an assumption about the presence of heat-resistant strains of viral diarrhea.
The virus is sensitive to disinfectants:
- trypsin;
- ether;
- chloroform;
- deoxycholate.
But not all is well here either. According to research by Huck and Taylor, viral diarrhea also has ether-resistant strains.
An acidic environment is capable of “finishing off” the virus. At pH 3.0, the pathogen dies within 4 hours. But it can survive in excrement for up to 5 months.
Because of this “resourcefulness” of the causative agent of viral diarrhea, today, according to various sources, from 70 to 100% of the total number of cows in the world are infected with this disease or were previously ill with this disease.
Sources and routes of infection
Viral diarrhea is transmitted in several ways:
- direct contact of a sick cow with a healthy animal;
- intrauterine infection;
- sexual transmission even with artificial insemination;
- blood-sucking insects;
- when reusing nasal forceps, needles or rectal gloves.
It is almost impossible to avoid contact between sick cows and a healthy herd. There are always up to 2% of infected animals in the herd. The reason for this is another way of spreading the infection: intrauterine.
Due to the latent course of the disease, many cows are able to calve already infected calves. A similar situation arises if there is an outbreak of an acute form of the disease in the early stages of pregnancy. The calf’s body, infected in the womb, recognizes the virus as “its own” and does not fight it. Such an animal secretes the virus in large quantities throughout its life, but does not show signs of illness. This feature contributes to the “success” of cow viral diarrhea among other diseases.
Since latently ill bulls and sires with an acute form of the disease secrete the virus along with sperm, cows can become infected through artificial insemination. Freezing sperm in liquid nitrogen only contributes to the preservation of the virus in the seed. In the body of cattle producers, the virus persists in the testes even after treatment. This means that a bull that has been ill and treated still remains a carrier of the bovine diarrhea virus.
The virus is also transmitted through blood. These are the usual non-sterilized instruments, reusable syringe needles or reuse of reusable ones and the transmission of the virus by blood-sucking insects and ticks.
Symptoms of bovine viral diarrhea
The usual incubation period is 6-9 days.There may be cases when the incubation period lasts only 2 days, and sometimes extends to 2 weeks. The most common clinical signs of viral diarrhea include:
- ulceration of the mouth and nose;
- diarrhea;
- high temperature;
- lethargy;
- loss of appetite;
- decrease in milk yield.
But the symptoms are often vague or poorly expressed. If there is insufficient attention, the disease can be easily missed.
A general set of symptoms that may occur with viral diarrhea:
- heat;
- tachycardia;
- leukopenia;
- depression;
- serous nasal discharge;
- mucopurulent discharge from the nasal cavity;
- cough;
- salivation;
- lacrimation;
- catarrhal conjunctivitis;
- erosions and ulcers on any mucous membranes and in the interhoof gap;
- diarrhea;
- anorexia;
- abortions in pregnant cows.
The specific set of symptoms depends on the type of disease. Not all of these signs of viral diarrhea are present at the same time.
Course of the disease
The clinical picture is varied and largely depends on the nature of viral diarrhea:
- acute;
- subacute;
- chronic;
- latent.
The course of the acute form of the disease varies depending on the condition of the cow: pregnant or not.
Acute course
In acute cases, symptoms appear suddenly:
- temperature 39.5-42.4 °C;
- depression;
- refusal of food;
- tachycardia;
- frequent pulse.
After 12-48 hours the temperature drops to normal. Serous nasal discharge appears, later becoming mucous or purulent-mucous. Some cows experience a dry, hard cough.
In severe acute cases, the cow's face may become covered with dried secretions. Further, pockets of erosion may form under the dry crusts.
In addition, viscous saliva is observed in cows hanging from their mouths.Catarrhal conjunctivitis develops with severe lacrimation, which may be accompanied by clouding of the cornea.
Round or oval foci of erosion with sharply defined edges appear on the mucous membranes of the oral cavity and the nasolabial mirror.
Sometimes the main symptom of viral diarrhea is lameness in cows, resulting from inflammation of the cartilage of the limb. Cows often lame throughout the entire period of illness and after recovery. In isolated cases, lesions appear in the interhoof gap, which is why viral diarrhea can be confused with foot and mouth disease.
During fever, the manure has its usual form, but contains mucous and blood clots. Diarrhea occurs only after a few days, but does not stop until recovery. Manure is foul-smelling, liquid, bubbling.
Diarrhea causes the body to become dehydrated. Over a long period of time, the cow's skin becomes hard, wrinkles and becomes covered with dandruff. Foci of erosion and crusts of dried exudate appear in the groin area.
Sick cows can lose up to 25% of their live weight within a month. Cows' milk yields decrease and abortions are possible.
Acute course: non-pregnant cattle
In young cows with strong immunity, viral diarrhea is almost asymptomatic in 70-90% of cases. With careful observation, you may notice a slight increase in temperature, mild agalactia and leukopenia.
Young calves aged 6-12 months are very susceptible to the disease. In this category of young animals, circulation of the virus in the blood begins on the 5th day after infection and continues up to 15 days.
Diarrhea in this case is not the main symptom of the disease. More often clinical signs include:
- anorexia;
- depression;
- decrease in milk yield;
- nasal discharge;
- rapid breathing;
- damage to the oral cavity.
Pregnant cows with acute disease shed less virus than those infected in utero. Antibodies begin to be produced 2-4 weeks after infection and persist for many years after clinical signs have disappeared.
Previously, viral diarrhea in nonpregnant cows occurred in mild forms, but since the late 1980s, strains causing severe diarrhea have appeared on the North American continent.
Severe forms were characterized by the acute onset of diarrhea and hyperthermia, which sometimes led to death. The severe form of the disease is caused by viruses of genotype 2. Initially, severe forms were found only on the American continent, but were later described in Europe. Viral diarrhea of the second type is characterized by a hemorrhagic syndrome, which leads to internal and external hemorrhages, as well as nosebleeds.
A severe form of the disease is also possible with a mutation of type 1 infection. In this case, the symptoms are:
- heat;
- mouth ulcers;
- eruptive lesions of the interdigital clefts and coronary region;
- diarrhea;
- dehydration;
- leukopenia;
- thrombocytopenia.
The latter can lead to pinpoint hemorrhages in the area of the conjunctiva, sclera, oral mucosa and vulva. In addition, after injections, prolonged bleeding from the puncture site is observed.
Acute course: pregnant cows
When pregnant, a cow exhibits the same signs as a single animal. The main problem of the disease during pregnancy is infection of the fetus. The causative agent of viral diarrhea is able to penetrate the placenta.
When infected during insemination, fertility decreases and the percentage of early embryo death increases.
Infection in the first 50-100 days can lead to the death of the embryo, while expulsion of the fetus will occur only after several months. If the infected embryo does not die within the first 120 days, a calf with congenital viral diarrhea is born.
Infection during the period from 100 to 150 days leads to the appearance of birth defects in calves:
- thymus;
- eye;
- cerebellum.
Tremors are observed in calves with cerebellar hypoplasia. They can't stand. Eye defects can lead to blindness and cataracts. When the virus is localized in the vascular endothelium, edema, hypoxia and cellular degeneration are possible. The birth of weak and stunted calves can also be caused by infection with viral diarrhea in the second trimester of pregnancy.
Infection between 180 and 200 days triggers a response from the now fully developed immune system. In this case, calves are born outwardly completely healthy, but with a seropositive reaction.
Subacute course
The subacute course with inattention or a very large herd can even be missed, since the clinical signs appear rather weakly, only at the onset of the disease and for a short time:
- temperature increase by 1-2 °C;
- rapid pulse;
- frequent shallow breathing;
- reluctant eating of food or complete refusal of food;
- short-term diarrhea for 12-24 hours;
- slight damage to the oral mucosa;
- cough;
- nasal discharge.
Some of these signs can be mistaken for mild poisoning or stomatitis.
In the subacute course, there were cases when viral diarrhea occurred with fever and leukopenia, but without diarrhea and ulcers on the oral mucosa. The disease can also occur with other symptoms:
- cyanosis of the mucous membranes of the mouth and nose;
- pinpoint hemorrhages on mucous membranes;
- diarrhea;
- increased body temperature;
- atony.
Viral diarrhea was also described, lasting only 2-4 days and resulting in diarrhea and decreased milk yield.
Chronic course
In the chronic form, signs of the disease develop slowly. The cows are gradually losing weight. Intermittent or constant diarrhea appears. Sometimes there may even be no diarrhea. Other signs do not appear at all. The disease can last up to 6 months and usually ends in the death of the animal.
Chronic diarrhea occurs in cows that are kept in inappropriate conditions:
- poor feeding;
- unsatisfactory living conditions;
- helminthiasis.
Also, outbreaks of the chronic form of the disease are present in farms where an acute form of diarrhea was previously recorded.
Latent flow
There are no clinical signs. The fact of the disease is determined by a blood test for antibodies. Often, antibodies to this viral disease are found even in clinically healthy cows from farms where diarrhea has never been recorded.
Disease of the mucous membrane
It can be classified as a separate form of the disease, which affects young animals aged 6 to 18 months. Inevitably leads to death.
The duration of this type of diarrhea ranges from several days to several weeks. It begins with depression, fever and weakness. The calf loses its appetite.Gradually, exhaustion sets in, accompanied by foul-smelling, watery, and sometimes bloody diarrhea. Severe diarrhea causes the calf to become dehydrated.
The name of this form comes from the ulcers localized on the mucous membranes of the mouth, nose and eyes. With severe damage to the mucous membranes, young cows experience severe lacrimation, drooling and nasal discharge. Lesions can also be in the interdigital gap and on the corolla. Because of them, the cow stops walking and dies.
This form of the disease occurs in prenatally infected young animals as a result of the “superposition” of their own virus on an antigenically similar pathogen strain from another sick individual.
Diagnostics
The diagnosis is made based on clinical data and the epizootic situation in the area. The final and accurate diagnosis is made after examining the pathological material. The virus isolated from the mucous membranes is differentiated from pathogens of other diseases that have similar symptoms:
- fungal stomatitis;
- foot and mouth disease;
- infectious ulcerative stomatitis;
- rinderpest;
- parainfluenza-3;
- poisoning;
- malignant catarrhal fever;
- paratuberculosis;
- eimeriosis;
- necrobacteriosis;
- infectious rhinotracheitis;
- mixed nutritional and respiratory infections.
For pathological studies, parts are selected where erosion of the mucous membranes is most pronounced. Such changes can be found in the gastrointestinal tract, lips, tongue, and nasal planum. Extensive foci of necrosis sometimes occur in the intestine.
Viral diarrhea affects the respiratory organs less. Erosion is present only in the nostrils and nasal passages. Mucous exudate accumulates in the larynx and trachea.Sometimes there may be bruising on the tracheal mucosa. Part of the lungs is often affected by emphysema.
Lymph nodes are usually unchanged, but may be enlarged and swollen. Hemorrhages are noted in the blood vessels.
The kidneys are swollen, enlarged, and pinpoint hemorrhages are noticeable on the surface. Necrotic foci are clearly visible in the liver. The size is increased, the color is orange-yellow. The gallbladder is inflamed.
Treatment of bovine viral diarrhea
There is no specific treatment for viral diarrhea. Symptomatic treatment is used. To stop diarrhea, astringents are used to reduce the loss of water from the body and avoid dehydration.
Forecast
With this disease, it is difficult to predict the mortality rate, since it depends on the strain of the virus, living conditions, the nature of the outbreak, the individual characteristics of the cow’s body and many other factors. The percentage of fatalities may vary not only in different countries, but even in different herds belonging to the same farm.
In the chronic course of diarrhea, 10-20% of the total number of livestock may become ill, and up to 100% of the number of sick people may die. There were cases when only 2% of cows fell ill, but they all died.
In acute diarrhea, the incidence rate depends on the strain:
- Indiana: 80-100%;
- Oregon C24V and related strains: 100% with case fatality rate 1-40%;
- New York: 33-38% with a case fatality rate of 4-10%.
Rather than treating and predicting the mortality rate among cows, it is easier to carry out prevention using a vaccine against bovine viral diarrhea.
Prevention of bovine viral diarrhea
The vaccine is used for cows in the 8th month of pregnancy and calves. For this category of cows, it is recommended to use a vaccine made from a virus weakened in rabbits. After double intramuscular injection of the vaccine, the cow receives immunity for 6 months.
In disadvantaged farms, serum from convalescent cows is used for prevention. If the virus is detected, the farm is declared unsafe and closed for quarantine. Sick cows are isolated from the herd until recovery or death. The premises are treated daily with disinfectant solutions. The farm is declared safe a month after the last sick cow recovers.
Conclusion
Cattle viral diarrhea is dangerous due to the variety of symptoms, high virulence and stability of the pathogen in the external environment. This disease can easily be disguised as many others, but if you miss the initial stage, it will be too late to treat the cow. Preventive measures also do not always yield results, which is why the disease is already widespread throughout the world.
