Content
An upset bowel movement is a common symptom of many diseases. Many of these ailments are not even infectious. Since diarrhea accompanies most infectious diseases, it may seem strange that cattle viral diarrhea is not a symptom but a separate disease. Moreover, in this disease, bowel dysfunction is not the main symptom.
What is viral diarrhea
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 speculum 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 milk yield. Viral diarrhea is common throughout the world. Only the virus strains may differ.
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 can be transmitted by blood-sucking insects and ticks, but later it was established that viral diarrhea of cows is not transmitted in this way.
There are 2 genotypes of viruses that cause infectious diarrhea in cows, but they do not differ in virulence. It was previously thought 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 widespread 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 the pathanotomy material at - 15 ° C it lasts up to 6 months.
The virus is not easy to "finish off" even at positive temperatures. It can withstand + 25 ° С during the day without decreasing activity. At + 35 ° C, it remains active for 3 days. The cow 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 everything is good here either. According to research by Huck and Taylor, there are also ester-resistant strains in viral diarrhea.
An acidic environment is capable of "finishing off" the virus. At pH 3.0, the pathogen dies within 4 hours. But in excrement it can persist up to 5 months.
Due to this "resourcefulness" of the causative agent of viral diarrhea, today this disease is infected or hurt earlier, according to various sources, from 70 to 100% of the total number of cows in the world.
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 of sick cows with a healthy herd. There are always up to 2% of infected animals in a 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 with an already infected calf. A similar situation occurs if an outbreak of an acute form of the disease occurs in the early stages of pregnancy. The body of a calf, infected while still in the womb, recognizes the virus as “its own” and does not fight it. Such an animal sheds the virus in large quantities throughout its life, but does not show signs of illness. This feature contributes to the "success" of viral diarrhea in cows among other diseases.
Since latently ill bulls and breeders with an acute form of the disease shed the virus along with the semen, cows can become infected with artificial insemination. Freezing semen in liquid nitrogen only helps to keep the virus in the seed. In the organism of cattle producers, the virus remains in the testes even after treatment. This means that a bull that has been ill and treated will still carry the cow's diarrhea virus.
The virus is also transmitted through blood. These are already familiar to everyone, non-sterilized instruments, reusable needles of syringes or reuse of reusable ones and transmission of the virus by blood-sucking insects and ticks.
Symptoms of cattle viral diarrhea
The usual duration of the incubation period is 6-9 days. There may be cases when the incubation period lasts only 2 days, and sometimes stretches up to 2 weeks. The most common clinical signs of viral diarrhea include:
- ulceration of the mouth and nose;
- diarrhea;
- high fever;
- lethargy;
- loss of appetite;
- decrease in milk yield.
But the symptoms are often blurred or poorly defined. With insufficient attention, illness can be easily missed.
A general set of symptoms that can occur with viral diarrhea:
- heat;
- tachycardia;
- leukopenia;
- depression;
- serous nasal discharge;
- mucopurulent discharge from the nasal cavity;
- cough;
- salivation;
- lacrimation;
- catarrhal conjunctivitis;
- erosion and ulcers on any mucous membranes and in the interdigital fissure;
- diarrhea;
- anorexia;
- abortion in pregnant cows.
The specific set of symptoms depends on the type of disease course. Not all of these signs of viral diarrhea are present at the same time.
Course of the disease
The clinical picture is diverse and largely depends on the nature of the course of viral diarrhea:
- sharp;
- subacute;
- chronic;
- latent.
The course of the acute form of the disease differs depending on the condition of the cow: pregnant or not.
Acute current
In an acute course, symptoms appear suddenly:
- temperature 39.5-42.4 ° C;
- depression;
- refusal of feed;
- tachycardia;
- rapid pulse.
After 12-48 hours, the temperature drops to normal. Serous nasal discharge appears, later becoming mucous or purulent-mucous. Some cows have a dry, hard cough.
In severe acute currents, the muzzle of the cow may become covered with dried secretions. Further, under dry crusts, foci of erosion can form.
In addition, viscous saliva hanging from the mouth is observed in cows. Catarrhal conjunctivitis develops with severe lacrimation, which may be accompanied by clouding of the cornea of the eye.
On the mucous membranes of the oral cavity and nasolabial speculum, round or oval foci of erosion with sharply defined edges appear.
Sometimes the main symptom of viral diarrhea is cow lameness, resulting from inflammation of the cartilage of the limb. Often, cows lame throughout the entire period of illness and after recovery. In isolated cases, lesions appear in the interdigital fissure, which is why viral diarrhea can be confused with foot and mouth disease.
During a fever, the manure is normal, but contains mucous membranes and blood clots. Diarrhea occurs only after a few days, but does not stop until recovery. The manure is offensive, thin, bubbling.
Diarrhea makes the body dehydrated.With a prolonged course, the cow's skin becomes tough, wrinkled and covered with dandruff. In the groin area, foci of erosion and crusts of dried exudate appear.
Affected cows can lose up to 25% of their live weight within a month. Milk yield in cows is decreasing, abortions are possible.
Acute course: non-fertile livestock
In young cows with strong immunity, viral diarrhea is almost asymptomatic in 70-90% of cases. On close observation, you may notice a slight increase in temperature, mild agalactia and leukopenia.
Young calves at the age of 6-12 months are very susceptible to the disease. In this category of young animals, the circulation of the virus in the blood begins from 5 days after infection and lasts 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;
- discharge from the nose;
- rapid breathing;
- damage to the oral cavity.
Acutely ill-nestled cows shed less virus than in utero infected cows. Antibodies begin to be produced 2-4 weeks after infection and persist for many years after the disappearance of clinical signs.
Previously, viral diarrhea in non-pregnant cows was mild, but since the late 1980s, strains have appeared on the North American continent that cause severe diarrhea.
Severe forms were characterized by an acute onset of diarrhea and hyperthermia, which sometimes led to death. The severe form of the disease is caused by genotype 2 viruses. 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 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 interdigital clefts and coronary spine;
- diarrhea;
- dehydration;
- leukopenia;
- thrombocytopenia.
The latter can lead to punctate hemorrhages in the conjunctiva, sclera, oral mucosa and vulva. In addition, after injections, prolonged bleeding from the puncture site is observed.
Acute course: pregnant cows
During pregnancy, the cow shows the same symptoms as the unmarried animal. The main problem of the disease during pregnancy is fetal infection. The causative agent of viral diarrhea can cross the placenta.
When infected during insemination, fertilization decreases and the percentage of early death of embryos increases.
Infection in the first 50-100 days can lead to the death of the embryo, while the expulsion of the fetus will occur only after a few months. If the infected embryo does not die within the first 120 days, then a calf is born with congenital viral diarrhea.
Infection in the period from 100 to 150 days leads to birth defects in calves:
- thymus;
- eye;
- cerebellum.
In calves with cerebellar hypoplasia, tremors are observed. They cannot stand. With eye defects, blindness and cataracts are possible. 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 within 180-200 days triggers a response from an already fully developed immune system. In this case, the calves are born outwardly perfectly healthy, but with a seropositive reaction.
Subacute course
A subacute course with carelessness or a very large herd can even be skipped, since clinical signs appear rather weakly, only at the onset of the disease and for a short time:
- temperature rise by 1-2 ° С;
- rapid pulse;
- frequent shallow breathing;
- reluctant food intake or complete refusal of food;
- short-term diarrhea within 12-24 hours;
- slight damage to the mucous membranes of the oral cavity;
- cough;
- discharge from the nose.
Some of these signs can be mistaken for mild poisoning or stomatitis.
In the subacute course, there were cases when viral diarrhea proceeded with fever and leukopenia, but without diarrhea and ulcers on the oral mucosa. Also, the disease can occur with other symptoms:
- cyanosis of the mucous membranes of the mouth and nose;
- pinpoint hemorrhages on the 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. Cows are gradually losing weight. Intermittent or persistent diarrhea appears. Sometimes even diarrhea may be absent. The rest of the signs do not appear at all. The disease can last up to 6 months and usually results in the death of the animal.
Chronic diarrhea occurs in cows that are kept in improper conditions:
- poor feeding;
- unsatisfactory conditions of detention;
- 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 established by analyzing blood for antibodies. Often, antibodies to this viral disease are found even in clinically healthy cows from farms where diarrhea has never been recorded.
Mucosal disease
Can be taken out in a separate form of the disease, which affects young animals aged 6 to 18 months. Inevitably fatal.
The duration of this type of diarrhea is 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 ulcers localized on the mucous membranes of the mouth, nose and eyes. With severe damage to the mucous membranes in young cows, strong lacrimation, salivation and nasal discharge are observed. Also, lesions can be in the interdigital cleft 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 "imposition" of its own virus on an antigenically similar strain of the pathogen from another sick individual.
Diagnostics
The diagnosis is made on the basis of 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 causative agents of other diseases that have similar symptoms:
- fungal stomatitis;
- foot and mouth disease;
- infectious ulcerative stomatitis;
- cattle plague;
- 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 on the gastrointestinal tract, lips, tongue, nasal mirror. In the intestine, sometimes there are extensive foci of necrosis.
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 bruises on the tracheal mucosa. Part of the lungs are 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 edematous, enlarged, punctate hemorrhages are visible on the surface. In the liver, necrotic foci are clearly expressed.The size is increased, the color is orange-yellow. The gallbladder is inflamed.
Treatment of viral diarrhea in cows
There is no specific treatment for viral diarrhea. Apply symptomatic treatment. Astringents are used to stop diarrhea to reduce water loss and dehydration.
Forecast
With this disease, it is difficult to predict the mortality rate, since it depends on the virus strain, livestock conditions, the nature of the outbreak, the individual characteristics of the cow's body and many other factors. The percentage of deaths may differ 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 can get sick, and up to 100% of the number of cases can 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 a case fatality rate of 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 prevent with a vaccine against viral bovine diarrhea.
Prevention of viral diarrhea in cattle
The vaccine is used for cows at the 8th month of pregnancy and calves. For this category of cows, a vaccine made from a virus attenuated in rabbits is recommended. After a double intramuscular injection of the vaccine, the cow gains immunity for 6 months.
In dysfunctional farms, serum from convalescent cows is used for prevention. If a virus is detected, the farm is declared dysfunctional and quarantined. Sick cows are isolated from the herd until they recover or die. The premises are treated daily with disinfectant solutions. The farm is declared safe a month after the last sick cow recovered.
Conclusion
Cattle viral diarrhea is dangerous due to the variety of symptoms, high virulence and resistance of the pathogen in the external environment. This disease is easily disguised as many others, but if you skip the initial stage, it will be too late to treat the cow. Preventive measures also do not always give a result, which is why the disease is already spread throughout the world.
