Sensitivity and Specificity of Multiple Technologies for the Detection of Confirmed Persistently BVDV Infected Cattle from a Feed Yard in South Texas

Etiology: Bovine Viral Diarrhea Virus (BVDV)

Bovine Viral Diarrhea Virus (BVDV) is a pathogen belonging to the genus Pestivirus of the family Flaviviridae. It is an enveloped, single-stranded RNA virus.

Economic Relevance: Bovine Viral Diarrhea leads to major economic loss in both beef and dairy industries, estimated to be approximately $2-3 billion annually in the US alone.

History: It was first reported in 1946 in Ithaca, New York, by researchers from Cornell University in a one-cow herd, with subsequent outbreaks of the disease showing morbidity of 33-88% and mortality of 4-8%.

Genome: BVDV has a positive-sense single-stranded RNA genome (ss (+) RNA), approximately 12.3 Kb in size. The genomic RNA contains one open reading frame of about 4000 codons, flanked by two untranslated regions (5'- and 3'-UTR).

Diagram Description: A linear representation of the BVDV genome showing the 5'UTR, Npro, Core, E1, E2, p7, NS2 (NS23), NS3, NS4A, NS4B, NS5A, NS5B, and 3'UTR, indicating structural and non-structural regions.

Citation: Vet. Res. 41 (6) 44 (2010). DOI: 10.1051/vetres/2010016. This is an Open Access article distributed under the terms of the Creative Commons Attribution-Noncommercial License (http://creativecommons.org/licenses/by-nc/3.0/), which permits unrestricted use, distribution, and reproduction in any noncommercial medium, provided the original work is properly cited.

Classification of BVDV

Cattle are the natural host of BVDV, but infection has been demonstrated in other species, including sheep, goats, wild ruminants, pigs, bison, alpacas, mouse deer, mountain goats, and white-tailed deer.

The virus is divided into two main genotypes:

• BVDV-1: Considered the most prevalent genotype.
• BVDV-2: Historically considered more virulent, causing severe disease.

Most recently, BVDV-3 or HoBi-like pestivirus has been classified as an atypical pestivirus.

Other pestiviruses include Classical Swine fever and Borders Disease Virus.

Note: More recent data has demonstrated that both genotypes (BVDV-1 and BVDV-2) can cause the same damage at respiratory and reproductive levels.

Further classification based on isolates:

• Non-cytopathogenic (ncp): Do not induce apoptosis and is the main source in PI cattle. NCP accounts for 95% of isolated BVDV.
• Cytopathogenic (cp): Induces apoptosis. The ncp biotype is the main frame to generate the cp biotype through mutations and reconventions.

Diagram Description: A phylogenetic tree illustrating the relationships among various pestivirus strains, with distinct branches for BVDV type 1 and BVDV type 2. Microscopic images labeled 'ncp' and 'cp' are also shown.

Citations: Vet. Res. 41 (6) 44 (2010). DOI: 10.1051/vetres/2010016. Open Access article under Creative Commons Attribution-Noncommercial License (http://creativecommons.org/licenses/by-nc/3.0/). Virol J. 2011 Feb 25;8:83. doi: 10.1186/1743-422X-8-83. Copyright Policy - open access http://openi.nlm.nih.gov/index.php.

BVDV Presence and Epidemiology

Presence: BVDV has a world-wide presence. Prevalence of seropositive cattle varies among countries and is influenced by vaccine use and management practices. In the USA, seropositive rates range between 40% and 90%. Unvaccinated herd-level prevalence varies from 28% to 53% depending on the region. PI prevalence is approximately 0.2% in the USA.

Epidemiology: From an epidemiological point of view, BVDV is very adaptable. It employs a combination of strategies to remain in a herd for extended periods. Persistent infection provides a unique ability for BVDV to survive by inducing immune tolerance through evasion of both innate and acquired immunity in utero. Laboratory techniques are the best way to detect the presence of BVDV and distinguish the form of the disease.

BVDV-Persistently Infected (PI) Creation

Diagram Description: A flowchart illustrating the creation of Persistently Infected (PI) BVDV cattle. It depicts pathways starting from insemination, leading to potential embryonic death or return to estrus if the ncp biotype is involved, resulting in persistent infection and immunotolerance. Alternatively, infection can lead to transient infection and seroconversion, or birth of a PI calf. PI calves can develop mucosal disease through mutation from ncp to cp. Transient infection can also result in abortion or malformation.

Citation: Vet. Res. 41 (6) 44 (2010). DOI: 10.1051/vetres/2010016. Open Access article under Creative Commons Attribution-Noncommercial License (http://creativecommons.org/licenses/by-nc/3.0/).

The Impact of BVDV PI Animals on BRD

Although the prevalence of PI-BVDV cattle in the USA is very low, the presence of only one PI-BVDV animal is well documented (Hay et al, 2016) to be a risk factor in feed yards for an increased rate of Bovine Respiratory Disease (BRD), cost of vaccination, antibiotic therapy, and mortality of unresolved BRD infections.

BVDV-PI cattle are more likely to become chronically ill or die than non-BVDV-PI cattle. Also, the probability for initial treatment with respiratory disease was 43% greater for cattle exposed to BVDV-PI cattle in the same pen or an adjoining pen (Loneragan; Journal of the American Veterinary Medical Association, 2005).

Diagram Description: A diagram outlining factors influencing Bovine Respiratory Disease (BRD). Preweaning factors include prenatal nutrition, intake of colostrum, preweaning health, temperament, preshipment management, preconditioning, vaccinations, and nutritional status. Postweaning factors include transportation/marketing stress, commingling, receiving period management, castration/dehorning, implant programs, receiving diet nutrients (energy, protein), minerals (Cu, Se, Zn), vitamins (E, antioxidants), and prophylactic antibiotics. These factors, along with the presence of BVDV (indicated by '?'), influence immunity and ultimately affect feedlot performance, feedlot health, and carcass quality.

BVD: Control and Management

Key strategies for controlling BVDV include:

• Biosecurity
• Vaccinations
• Diagnostics

Study Rationale & Objectives

Rationale: There was a request from the Kansas Farm Bureau in South East Kansas to regulate BVDV in their region by making it a reportable disease. The SNAP BVDV Antigen Test was yielding some discrepant results when compared to testing in VDLs. The application of highly sensitive and specific diagnostic technologies is fundamental to accurately identify those low prevalent PI-BVDV animals for the implementation of control strategies.

Objective: To compare the sensitivity and specificity performance of:

• Immunochromatographic strip (SNAP Test)
• Antigen Capture ELISA (ACE)
• Applied Biosystems RT-PCR VetMAX™ Gold BVDV PI Detection Kit

Materials and Methods

Two samplings, with three weeks apart, were performed on previously confirmed PI-BVDV (n=37) and BVDV-negative (n=20) cattle from a feed yard located in South Texas, USA. The feed yard held 24,000 cattle and kept PI-BVDV in a single pen until slaughter time (~n=48).

Diagram Description: A map of the United States highlighting Texas. An image shows cattle ear notching for sample collection. Another image shows a cow with an ear tag.

During the first sampling, five ear notches from each animal were collected in a single day and shipped overnight to the Kansas State Veterinary Diagnostic Laboratory (KSVDL) for processing with the following diagnostic technologies:

Two weeks later, resampling of the same set of animals (n=57) was carried out to be tested with IHC and BVDV RNA sequencing as the gold standard methods. True positive or true negative results were determined based on the combined results from at least 1 out of the 2 gold standard methods.

Results

Table 1: Result of the real-time PCR testing, SNAP test, and Antigen Capture ELISA.

• VetMAX-Gold BVDV PI Detection Kit is more sensitive than the other methods.
• Missing some of the PI-BVDV animals when utilizing technologies with low sensitivity will generate false-negative results, allowing PI-BVDV cattle to be undetected and continue commingling with BVDV-negative cattle, which is very detrimental for the health status of a herd.

Discussion and Conclusions

All of the diagnostic technologies tested in this study offered a good but different level of sensitivity and an equal level of specificity.

However, the real-time PCR technology tested was more sensitive than the antibody-based methods.

The practical implication of using diagnostic technologies with low sensitivity (e.g., 91.67% and 94.44%) with a disease of very low prevalence (0.2%-0.4%) such as PI-BVDV in the US is of significant importance.

Diagram Description: Three flowcharts illustrate the breakdown of a population of 24,000 cattle for each diagnostic test, showing the number of True Positives, False Negatives, False Positives, and True Negatives.

• SNAP Test: Population 24000 (48 Sick, 23952 Well). Results: 44 True positive, 4 False negative, 0 False positive, 23952 True negative.
• ACE: Population 24000 (48 Sick, 23952 Well). Results: 45 True positive, 3 False negative, 0 False positive, 23952 True negative.
• VetMAX™ Gold BVDV PI Detection Kit: Population 24000 (48 Sick, 23952 Well). Results: 48 True positive, 0 False negative, 0 False positive, 23952 True negative.

The current study reveals substantial practical differences in diagnostic methods that can be used as management tools in controlling BVDV and ultimately reducing the incidence of BRD.

Acknowledgments

• KSVDL
• South Texas Feed Yard
• Thermo Fisher Scientific

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