Study on Major Respiratory Viral Diseases of Cattle

Bovine respiratory disease syndrome (Bovine resprratory disease COrn-plex, BRDC) is a general term for diseases such as bovine pneumonia, bronchitis, viral diarrhea, etc., caused by a single or mixed infection of viruses or bacteria. BVDV, IBRV, BPIV3 and BRSV are important viral pathogens that are known to cause bovine respiratory disease syndromes. Their infections lead to reduced immunity of cattle and secondary bacterial infections, resulting in serious bovine respiratory diseases. 

Understanding and grasping the prevalence of the above four viral diseases in dairy cows and beef cattle in my country's main cattle-raising areas is of great significance to the prevention and control of bovine respiratory disease syndrome in my country. The author explored the pathogenesis, clinical manifestations and pathogenic mechanism of bovine viral diarrhea virus, and provided a theoretical basis for epidemic surveillance and integrated disease prevention.

Domestic and foreign studies have shown that the main viral pathogens isolated from sick cattle with respiratory diseases are bovine viral diarrhea virus (BVDV) and bovine infectious rhinotracheitis virus(IBRV), bovine parainfluenza type 3 virus (BPV) and bovine respiratory syncytial virus (BRSV). Among the four main viral pathogens that cause bovine respiratory diseases, except BVDV and IBRV alone.

Infection can cause serious clinical morbidity. BPIV3 and BRSV virus infections of cattle alone are often recessive infections, without any clinical symptoms, or only mild clinical symptoms.

Bovine viral diarrhea virus (Bovine vh-al diarrhea virus, BVDV), also known as bovine viral diarrhea, mucosal disease virus or mucosal virus, represents a group of single-stranded RNA viruses.The composition of different pestiviruses is in the pestivirus house of Flaviviridae. Viruses in members of the pestivirus genus were once considered host-specific, but later studies have shown that BVDV and DBV can infect more.A wide range of hosts, they can not only infect cattle and sheep, but also a variety of cloven-hoofed animals including pigs.

Clinical manifestations and pathogenic mechanism of BVDV

1. Subclinical infection

In cattle with healthy immune function and negative serum reaction. About 70%-90% of BVDV infect cattle without showing clinical symptoms, that is, in a subclinical infection state.

Related tests have shown that BVDV infection mostly leads to leukopenia, mild fever and the production of serum neutralizing antibodies. After dairy cows are sick, subclinical infections can lead to reduced milk production.BVDV generally replicates and proliferates in adjacent lymphoid tissues and the upper respiratory tract.

2. Acute infection

Acute BVDV infection is the most common, with a relatively high incidence and a low mortality rate. It usually occurs in sero-negative cattle at 6-24 months of age. Main clinical symptoms.For depression, high fever, leukopenia, anorexia, diarrhea, runny nose, occasional oral ulcers or erosions, oral bleeding and pustules, and decreased milk production during lactation, breast and skin intercourse.

Skin ulcers can be seen at the boundary. Acute BVDV in newborn calves may cause symptoms of pneumonia and enteritis. Researchers believe that the appearance of this symptom is related to the insufficient passive immunity of the calf.Carprofen injection, an adjuvant of antibacterial drugs for cattle infection with acute respiratory diseases, is used to reduce clinical symptoms.

3. Severe Acute

After cattle become ill, the morbidity and mortality increase, which occur at all ages. The necropsy of infected cattle showed lesions such as bleeding, ulcers, and congestion on the gastrointestinal surface, similar to mucosal diseases. The new BVDV virus group that caused this disease is defined as BVDV2. Hemorrhagic syndrome and thrombocytopenia are a form of severe acute bovine viral diarrhea virus infection.

4. Persistent infection

Persistent infection is a way for BVDV to maintain its existence in the natural environment. It is mainly caused by uterine infection of NCP BVDV in cattle in early pregnancy. Persistently infected calves mainly show symptoms such as premature birth, congenital defects, stunted growth, breastfeeding difficulties, and lethargy. BVDV can also infect susceptible cattle and cows through artificial insemination in the semen of persistently infected bulls, but it is rarely caused by direct mating of infected bulls.

BVDV control measures

First of all, we must strengthen cattle breeding management, minimize various stress responses, avoid overcrowding, and clean up the breeding environment in time. Pay attention to strengthening nutrition and frequent observation, should be treated or removed in time.

Cows with respiratory diseases in the herd. In addition. Carprofen injections, vaccines and antibiotics, which are auxiliary agents of antibacterial drugs to reduce clinical symptoms, are still important means for prevention and treatment. Inactivated vaccines are safe for pregnant cattle, but their immunity period is short. Attenuated vaccines have a long immunization period, but are not safe for pregnant cattle. Therefore, vaccines should be selected according to different immunization subjects and immunization procedures.