Infectious bovine Rhinotrachieitis (IBR): A highly neglected disease with greater economic impact on farmers
Dr. Shailendra Singh1, Dr. Shailesh Kumar Patel1, Dr, Jigyasa Rana2
1Department of Veterinary Pathology, College of Veterinary Science and A.H., Rewa, M.P. – 486001
2Department of Veterinary Anatomy, Faculty of Veterinary and Animal Sciences, RGSC, BHU, Barkachha, Mirzapur, U.P. – 231001
Introduction
Bovine herpes virus-1 (BHV-1) is one of the most important viral infections of cattle which cause severe respiratory infection, conjunctivitis, abortion, vulvovaginitis and balanoposthitis (OIE 2008). It is a disease of cattle that is responsible for significant economic losses worldwide. The BHV-1 is a member of the genus Varicellovirus in the subfamily Alpha herpesvirinae, which belongs to the Herpesviridae family. The virus is associated with major clinical syndromes, namely IBR, infectious pustular vulvovaginitis (IPV) and infectious pustular balanoposthitis (IPB). The virus also causes other clinical syndromes such as abortion, infertility, conjunctivitis, enteritis and encephalitis. The disease is also known as red nose, necrotic rhinitis or dust pneumonia.
In the year 1955, at a meeting of the US livestock sanitary association, the accepted name for the disease became infectious bovine rhinotracheitis. The main sources of the virus are nasal exudates and cough droplets, genital secretions, semen, fetal fluids and tissues. These materials can be transmitted by direct contact with infected animals or by indirect contact with infected material and personnel. The BHV-1 has the ability to remain in the latent form following a primary infection with a field isolate or vaccination with an attenuated strain. The virus is usually detectable in the sensory ganglia of the trigeminal nerve in IBR and in the sacral spinal ganglia in IPV/IPB. Latency may also occur in tonsillar lymphoid cells and peripheral blood lymphocytes. Viral reactivation may occur owing to stressful stimuli associated with delivery, transport or animal, insufficient herd management, co-infections, superinfection, treatments with corticosteroids, or parturition (Winkler et al., 2000). As a result, the reactivated virus may be re-excreted and an increased neutralizing antibody titer may be observed. Latently infected animals should always be considered as a potential source of infection (Bitsch, 1973).
Etiology
IBR is caused by Bovine Herpesvirus-1 (BHV-1). It belongs to family- Herpesviridae, sub family- Alphaherpesvirinae and genus- Varicellovirus. Herpesviruses are large, enveloped, double-stranded DNA viruses (Harrison 2001). Typical herpesvirus virions consist of a core containing linear double-stranded DNA, an icosadeltahedral capsid of about 100 nm diameter containing 162 capsomeres, a tegument surrounding the capsid, and an envelope containing viral glycoprotein spikes on its surface. All herpesviruses encode a large number of proteins involved in nucleic acid metabolism, DNA synthesis and protein processing. There are 8 known glycoproteins: gB, gC, gD, gE, gH, gI, gK and gL; the major envelope glycoproteins are gB, gC and gD. The gC, gD, gE, gG, gI, UL49h and thymidine kinase genes are involved in viral virulence (Roizman and Pellett 2001).
Epidemiology
The BHV-1 is currently distributed globally (Rajkhowa et al., 2004). Several European countries successfully implemented the IBR eradication program. Countries like Austria, Denmark, Finland, Sweden, and Switzerland are officially free of IBR (Ackermann and Engels 2005). Like other countries, India was also affected by this disease as the virus was detected in many parts of the country, like Gujarat, Tamilnadu, Orissa, Arunachal Pradesh and Nagaland (Rajkhowa et al., 2004).
Economic Importance
IBR is not a highly fatal disease but it can cause considerable economic losses due to abortion, loss of body condition, reduced milk yield and loss of new born calves, temporary failure of conception, insufficient feed conversion, secondary bacterial pneumonia and cost of treatment. Morbidity and mortality rates vary considerably and were lower in dairy herds (8% morbidity and 3% mortality) than in beef cattle. In feed lots the mortality rate may reach upto 20-30% and rarely up to 100 (Barenfus et al., 1963). Screening, surveillance and monitoring is important to maintain the herd health status and to decrease the economic losses caused by this disease (Raizman et al., 2011).
In India, no such estimates have been made till date, but the epidemiological surveys indicate a substantial loss due to the disease. Morbidity rate of 90% and mortality rate of 30% was recorded in an outbreak of nervous form of disease in Australia (Gardiner et al., 1964). Conception rate fall down from 80% to 45-50% in majority of cows suffering from herpes vulvovaginitis due to artificial insemination (Laveso et al., 1984)
Transmission
Direct contact (e.g. nose to nose) is the most important method by which IBR virus is transmitted from infected animal to a susceptible animal. The virus can also spread through air between animals over short distances of 3-5 meter. The BHV-1 can be shed during primary and secondary infections and following reactivation. The main routes of shedding are in fluid from the nose, eyes and mouth, in the semen of bulls, in fluids from the female reproductive tract. Unlike other pathogens, IBR virus transmission is not thought to commonly occur via milk or faeces. Latently infected animals do not continuously shed virus. The latent virus must first reactivate (usually following a period of stress or immune suppression) and then shedding may occur for a limited period of time (around 10-20 days).
Clinical Signs
The BHV-1 is an important cause of respiratory infection, abortion, conjunctival infection, and other respiratory tract diseases. The clinical manifestation of BHV-1 infection depends on the nature of various subtypes. The BHV-1 causes three different types of infection, namely respiratory infection (BHV-1.1), genital infection (BHV- 1.2), and neurological disease (BHV-1.3/BHV-1.5). The respiratory infection is characterized by high fever, mucopurulent nasal discharge, and excessive salivation. The lesion includes rhinotracheitis, pharyngitis, and laryngotracheitis. The virus with co-infection might induce severe bronchopneumonia, and pleuritis.
Control
Control measures include normal hygienic measures and maintaining 2-3 weeks of quarantine period before introducing new animals to the herd and exclusion of positive animals, use of live attenuated or whole virus vaccines, and removal of semen from positive animals. Successful eradication requires strict import restriction on cattle, semen and embryos because the reintroduction of the virus into these immunologically naive populations is likely to have serious consequences and lead to severe economic loss. If a cow with clinical BHV-l infection is diagnosed, the whole herd may be vaccinated to protect the animals from disease, if there is a clinical outbreak of BHV-l in the close vicinity.
Effective monitoring and control measures are required to avoid the risk of reintroducing BHV-1 into BHV-1 free herds/ farms. Good farm management practices, zoo-sanitary and hygienic measures should also be adopted. The WOAH guidelines recommend 2-3 weeks quarantine period for newly introduced cattle after which only BHV-1 sero-negative cattle are introduced to the herd.
The use of the marker vaccines is advocated as it offers the differentiation of vaccinated and naturally infected animals. Besides, there should be strict isolation of the affected animals along with control of movement.
References
Available on request at drshailendravet78@gmail.com.
