Diagnosis and Control Measures of Bovine Infectious Rhinotracheitis Explained
Many cattle farmers have encountered problems with cattle showing difficulty breathing, purulent nasal discharge, and congestion of the nasal mucosa. When these symptoms appear, attention must be paid, because combined with epidemiology, the cattle have likely contracted infectious rhinotracheitis. Bovine infectious rhinotracheitis, also known as "necrotic rhinitis" and "red nose disease," is a contact infectious disease of the cattle respiratory tract caused by Bovine herpesvirus type I (BHV-1). This disease is prevalent worldwide and has a significant impact on the milk production of dairy cows, the reproductive capacity of bulls, and the working capacity of draft cattle. Below, QinNong Net provides a detailed introduction to the diagnostic points and control measures for this disease:
I. Clinical Symptoms
The incubation period of bovine infectious rhinotracheitis virus is 1 to 3 days for artificial infection and generally 4 to 7 days for natural infection, sometimes reaching more than 20 days. The disease can present five clinical types.
1. Respiratory type
This is the most important type. It may manifest as a very mild, unnoticeable infection, or as a very severe disease. It often occurs after moving to a new barn or after being transferred from pasture to indoor housing. In acute cases, the entire respiratory tract is mainly affected, followed by the digestive tract. At the onset, body temperature suddenly rises (40 to 42°C), with severe depression, anorexia, and a large amount of mucopurulent nasal discharge. The nasal mucosa is highly congested and fiery red (hence the name "red nose disease") with superficial ulcers appearing, and necrosis of the nasal alae and nasal planum. Because the nostrils are filled with inflammatory exudate, breathing becomes highly difficult, even to the point of open-mouth breathing. Conjunctivitis and lacrimation may be seen, and the exhaled breath has a foul odor due to necrosis of the nasal mucosa. Respiratory rate increases, and coughing from the deep bronchi is frequently heard. Blood-tinged diarrhea may sometimes be seen.
2. Genital type
At the onset, mild fever is usually present. Severely infected animals show tail raising and restlessness, frequent urination with signs of pain, edematous swelling of the vulva, and vulvar hair stained with bloody exudate. The initial symptom is redness of the vaginal mucosa and formation of pustules, which give the vestibular and vaginal walls a granular appearance. Then mucous to mucopurulent exudate accumulates on the floor of the vagina. In some cases, the pustules increase in number and coalesce, subsequently forming an extensive gray necrotic membrane on the vestibular and vaginal walls; when wiped or sloughed off, a reddened abraded appearance remains. This type generally does not involve abortion. The disease course is generally about 2 weeks, and if complications occur, it may reach 3 to 8 weeks. In male animals, it manifests as infectious pustular balanoposthitis; the lesions of the glans penis and prepuce resemble those of the vulva and vagina, with the affected tissues showing pustule formation and a granular, granulation-like appearance. When edema of the prepuce and penis causes posthitis, scrotal swelling occurs, but orchitis has not been confirmed.
3. Conjunctival type
Due to the virus's affinity for the mucous membranes of affected cattle, it can sometimes cause keratoconjunctivitis, usually without corneal ulceration. This type of infection generally has no obvious systemic reaction, and the respiratory type may sometimes occur simultaneously. Generally, there may be subconjunctival edema, on which a gray necrotic membrane may form, creating a granular appearance; the cornea may become mildly cloudy, and affected cattle have seropurulent discharge from the eyes and nose.
4. Abortion type. In some cases, wild-type virus or artificially attenuated virus (vaccine) can cause abortion in cattle, usually seen at any stage of pregnancy in first-calf heifers. The incidence of abortion cases caused by this virus is still unclear, but in recent years it has been found that abortion cases have decreased, which may be due to improved diagnostic methods and increased awareness of the disease. In many cases, an undiagnosed respiratory infectious disease may have been prevalent in the herd 1 to 2 months before the abortion occurred. The virus has been isolated from aborted calves, and inoculation of this virus into susceptible heifers can cause abortion.
5. Encephalitis type
The disease can manifest as meningoencephalitis. It has been reported in the United States, Australia, and other countries, but the incidence is very low. Affected cattle are characterized by ataxia, depression, followed by excitement, frothing, convulsions, and finally recumbency, opisthotonus, leg paddling, and teeth grinding. The disease course is short, and death usually occurs.
Overall, the disease course varies greatly depending on the severity of onset. Mild cases are difficult to detect. Some respiratory or encephalitis cases may die within hours after symptoms are noticed, while most cases have a disease course of several days. Morbidity and mortality also vary greatly, depending on the virulence of the virus, the age of the affected cattle, the clinical type, the herd's feeding and management conditions, and body condition.
II. Diagnostic Points
When affected cattle die, necropsy findings of fibrinous exudate in the nasal cavity and trachea are indicative lesions of the disease.
Diagnosis of the conjunctival type is less difficult. The granular appearance, fibrinous necrotic membrane, subconjunctival edema, and seropurulent discharge from the eyes and external nares are prominent lesions of the disease. When catarrhal conjunctivitis occurs with upper respiratory tract infection, it helps support the diagnosis of the disease. Likewise, clinical diagnosis is not difficult for any bull or cow showing the genital type.
For abortion caused by this virus, diagnosis can be made with the help of virus isolation (the virus can be isolated from fetal thoracic fluid or fetal membranes). During abortion, the antibody titer in the cow's serum increases. The encephalitis type of the disease can also be diagnosed by virus isolation and histopathological examination.
For virus isolation, disease material can be collected from lesioned areas, preferably during the febrile period. The virus can be isolated using tissue cultures such as bovine kidney cells or porcine kidney cells. Preliminary identification of the virus can be determined based on its rapid production of characteristic cytopathic effects in tissue culture (cells become round, shrink, granules enlarge and aggregate, and finally detach). Serum neutralization tests and fluorescent antibody examination can also be used as diagnostic indicators.
III. Control Measures
There is no specific treatment for this disease. The role of broad-spectrum antibiotics is to prevent secondary bacterial infection, and the use of comprehensive symptomatic treatment can reduce mortality. Recovered cattle can obtain lifelong immunity. Vaccination is an important measure for preventing this disease. Generally, calves around six months old are vaccinated, and immunity is produced 10 to 14 days after vaccination; 9% of immunized cattle can retain antibodies in their bodies for a relatively long time. Calves can obtain passive immunity for 2 to 4 months by drinking colostrum from the cow. Pregnant cattle cannot be vaccinated, as it may cause abortion.
Strengthening feeding and management, improving sanitary conditions, and implementing epidemic prevention and isolation measures can prevent the spread of this disease. However, because susceptible cattle are highly sensitive to this disease, these measures can only limit the widespread spread of the active or latent forms. A large number of survey results show that 10%-96% of cattle positive for serum antibodies are latent infection sources; therefore, the use of vaccines remains the main measure for controlling this disease. If complications are to be controlled, symptomatic treatment can be adopted. For example, in the respiratory type, when bacterial complications are confirmed, sulfonamides and antibiotics can be used, but the problem of these drugs remaining in milk and meat should be considered. For pustular vulvovaginitis and balanoposthitis, topical antibiotic ointments can be applied to reduce sequelae.
The above is the diagnosis and control of bovine infectious rhinotracheitis. As mentioned above, there is no specific treatment for this disease. Therefore, doing a good job in daily protection, properly isolating affected cattle, and timely use of vaccines for control are key. QinNong Net will also continue to follow the progress of treatment methods for this disease, and will inform farmer friends as soon as there is a confirmed specific treatment.