Scientect

Authors: Truong Khiet Lam
Affiliation: School of Biosciences, Nottingham University, Malaysia.

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Introduction

Among infectious diseases found in ruminants globally, the bovine viral diarrhoea (BVD) virus is capable of bringing pathological damage to cattle hosts that it infects but also economic damages to farmers. The term bovine is derived from the Latin word Bovidae, meaning cow, and denotes any hoofed mammals that belong to the family Bovidae, such as cattles, sheeps, and goats. Hence, bovine viral diarrhoea virus is a virus that affects these animals, particularly cattle. In this article, the name of the virus will be abbreviated as BVDv in some paragraphs for the purpose of convenience.

The Virology of Bovine Viral Diarrhoea virus (BVDv)

Bovine viral diarrhoea virus (BVDv) belongs to the genus Pestivirus of the Flaviviridae family. Virions (particles of a virus) of Flaviviridae share the common characteristics of having a spherical shape of 50 nm in diameter coated with a lipid envelope. The first case of infection by this virus was first reported in New York, in 1946, by C.G Rickard and P. Olafson, and later published in an article in April 1, 1947, under the title of ‘New transmissible disease by virus diarrhoea in cattle.’ 

Viral RNA genome of Pestivirus is positive-sense, single-stranded ( (+) ssRNA) and is about 11-13 kB in length. The main difference between positive or plus(+) stranded and negative or minus(-) stranded viruses is that the genomes of positive stranded virus have functional mRNAs, which means that these genomes are translatable by the host cell right after penetration, allowing for replications of viral proteins. The majority of known viruses, including several pathogens in humans, possess this type of genome. One primary example for (+) ssRNA virus is the severe acute respiratory syndrome (SARS) virus of the Coronaviridae family, otherwise known as SARS-Coronavirus. The SARS-CoV 2 strain of the SARS virus is responsible for causing COVID-19.  

BVDv is teratogenic in nature, meaning that the foetal of the infected cattle, usually in their gestational stage, is most likely to suffer defects of bodily functions and physique, or even premature death. Viral replication of BVDv attacks and destroys the number of cells of both innate and adaptive immune systems, including macrophages and neutrophils, and T and B-lymphocytes, respectively. The immune system of persistently-infected cattles are found to be compromised, or suppressed, and is therefore unresponsive to BVDv, and hence these animals often die young after being infected throughout their lives. 

Epidemiology of BVDv in cattle

BVDv is found in cattle worldwide, and there is no known region in the world that is unaffected by the virus. Once a single cattle is infected, the virus spreads quickly and soon become prevalent in the whole herd.  

BVDV infection in cattle are classified into two genotypes: BVDv-1 and BVDv-2, but studies have found that the BVDv-1 is more prevalent in herds.

The epidemiology of BVDv infection depends on many risk factors like farming practices and density of the herd. On the same page, numerous studies have found that a smaller, less dense in number herd has a better at pathogen clearance (when the immune system rids or ‘cleans’ itself of a disease) than a herd that is more packed. 

Economic losses caused by BVDv infection in cattle

For lower and middle-income countries, like Asian and African countries whose economy relies heavily on farming and agriculture, BVDv poses a huge threat to the core of these countries’ income: their livestock and in turn, their livelihood. 

In the dairy sector, yield of milk is reduced along with poor reproductive ability, and for the meat sector, the main reasons for reduced meat production are caused by high mortality rate and induced abortion of foetus in the early stage of pregnancy, all of which are pathological results of BVDv infection. This situation in which BVDv pathogenesis is in effect is the main contributor to what is called ‘direct economic losses.’ Indirect losses are expenses spent on methods of prevention in disease control programs such as diagnostic tests, vaccination, and culling.

Conclusion

As of now, there is currently no standard treatment for BVDv, and there is little that is studied in the epidemiology of BVDv and its consequences in lower – and middle income countries. However, farmers worldwide can take in account the costs that are used in prevention methods of BVDV, such as diagnosis and vaccination, to measure against the potential economic losses that they will go through in encountering infections caused by bovine viral diarrhoea virus.

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