BOVINE VIRAL DIARRHEA OVERVIEW OF SASKATCHEWAN LABORATORY TESTING 2015 - 2016

February 28, 2017

In this report:

BVD importance

Diagnostic tests

offered by PDS

Testing overview

Test results

Changes trends

Report limitations

Prairie Diagnostic Services Endemic Disease Report

Disease importance

Bovine Viral Diarrhea (BVD) remains the most economically important viral disease for the Saskatchewan beef cattle industry and one of production limiting diseases for the dairy industry. It importance is defined by reproductive loss, aggravation of respiratory diseases in calves, immunosuppression and resulting increased susceptibility to other diseases, feedlot losses due to mucosal disease, direct production loss, and treatment cost. The Saskatchewan government provides support to producers affected by BVD through the BVD Screening and Control Program. This initiative covers the cost of testing in sick, dead, deformed, or aborted calves submitted under the program. It will also cover testing of yearlings with clinical signs of BVD if they still reside on the farm of birth.

Diagnostic tests offered by PDS

Testing overview: animal species

Most of the BVD diagnostic work performed by PDS in 2016 was done on samples obtained from cattle (211 cases > 2194 animals > 2200 samples > 2254 tests). Samples were also submitted from bison (7 cases > 21 animal > 22 samples > 32 tests), alpaca (1 case > 7 animals > 7 samples > 7 tests) and a goat (Figure 1). BVD diagnostic work performed in 2015 was similar, with the majority of testing done on cattle (234 cases>1712 animals>1725 samples>1788 tests) and the reminder on samples from bison (9 cases > 21 animal > 22 samples > 22 tests), alpaca (1 case 7 animals/7 samples/7 tests), sheep (one case/24 animals/24 samples/24 tests), and goats (two cases/two animals/two samples/two tests) were tested (Figure 2).

Science and art of counting laboratory submissions

There is more than one way to count laboratory submissions:

by case (one submission

event with assigned Case Number);

by sample source (there

might be more than one animal submitted; for example, three carcasses in one case - each gets a unique Sample Source ID);

by sample (there might be

multiple samples submitted in one case or derived from one sample source) - each gets a unique Sample ID;

by test - each ordered test

gets a unique Test Ordered ID

For the purposes of this report the default analyses will be performed on the number of conducted laboratory tests unless specified otherwise.

Overall, compared to 2015, PDS conducted 20% more tests and 21% more animals

were tested for BVD in 2016. Due to particular importance of BVD to the cattle industry

and insignificant number of submissions from other species, further analysis pertains only

to bovine submissions.

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Test name Target Specimens Diagnostic value Immunohistochemistry BVDV antigen Formalin-fixed skin biopsies ≥ 6 mm or ear notch-

es Paraffin-embedded tissues

Positive diagnosis for persistent infection

Polymerase Chain Reaction BVDV gene EDTA whole blood, tissue or culture Positive diagnosis Virus Isolation BVDV Ileum, lymphoid tissue, or kidney.

For PI cattle >6 months – serum. For PI cattle< 6 months – EDTA or Heparin for

buffy coat For acute infection – EDTA or Heparin for buffy

coat

Positive diagnosis

Fluorescent Antibody BVDV antigen Abortion cases – kidney (fetus) Older animals – lung, lymph node, spleen, kidney

or intestine Positive diagnosis

Virus Neutralization BVDV antibodies Serum History of exposure to BVDV, recent infection (paired

testing), vaccination efficacy

Testing overview: number of tests per bovine case

A closer look at the number of tests per case shows that individual animal diagnostic submissions (1 test per case) were slightly

lower in 2016 (137 case in 2016 vs. 156 cases in 2015), but there were more group screening submissions (40 submissions with

over 10 samples/case in 2016 vs 31 in 2015) (Fig. 3 and 4).

Testing overview: number of bovine tests by laboratory method

Not all BVD tests are created equal

There are five different types of laboratory tests developed for BVD diagnostic purposes:

Detecting a live virus (Virus

Isolation) is the “gold standard’”, but it is labor intensive, takes a long time to complete, and requires special care in sample collection and transport to maintain virus viability. This makes it less suitable for routine diagnostic purposes;

Detecting host’s immune response

to BVD virus (Serum Neutralization) is a practical tool for diagnosing acute BVD infection (two samples collected 21 days apart required), history of animal’s exposure to BVDV, or gauging an immune response to BVDV vaccine;

Detecting presence of BVDV

genetic material (RNA) by polymerase chain reaction (PCR) is a sensitive, reliable, and fast method to detect presence of the virus. It is useful in acute or persistent BVDV infection cases;

Detecting presence of BVDV

antigen in animal tissues by application of fluorescent antibodies. This method is most useful for diagnostic investigation of abortions and clinical cases;

Immunohistochemistry also relies

on detection of viral antigens. It is especially useful for detection of persistently infected (PI) animals. This method is the most practical and economical tool for herd screening.

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Immunohistochemistry remains the predominant method used for BVD diagnostic

testing in cattle (91% of all tests in 2016 and 86% in 2015).

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Testing overview: temporal distribution of bovine tests

per laboratory method

When is the best time to test for BVD?

There are few considerations on strategic timing for BVDV testing:

All animals entering the herd

should be quarantined and tested;

Early gestation is the most critical

time to avoid exposure to BVDV in pregnant animals ;

It is convenient to use ear notches

collected at branding for IHC BVD testing;

The Saskatchewan BVD

Screening and Control Program, funder under Growing Forward 2, provides free testing of BVD suspects (dead, deformed, aborted and stillborn calves or yearlings with clinical symptoms residing on the farm of birth). Call 306-798-0253 for more information.

The best time to start the BVDV testing program is NOW!

There are distinct seasonal trends in bovine BVD testing related to the primary reason for diagnostic inquiries (Figures 7 and 8):

Abortions investigations ( January to April) (fluorescent antibody, STET PCR, and serum neutralization testing);

Fall clinical cases investigations (September to December) (real-time PCR, and serum neutralization testing);

Herd screening (throughout the year, but peaking during branding (May—July) (immunohistochemistry testing).

Bovine BVD testing results by test method*

* Serum Neutralization testing results not in-

cluded in this analysis

There were 33 positive BVDV tests from 13 cases recorded in 2016 and 35 from

19 cases in 2015. (Figures 9 and 10).

Photo Caption

Bovine BVD positive tests: temporal distribution

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Bovine BVD positive cases: spatial distribution

Bovine BVD positive cases: temporal distribution

Personal information? It is protected!

Spatial distribution of positive cases and tests is an important analysis tool for disease management and planning control measures. However, specific locations of affected animals might disclose personal information about their owners.

Usage and distribution of sensitive information in Saskatchewan is protected by the Personal Information and Electronic Documents Act (PIPEDA) . PDS has a client service agreement in place defining rules for data collection, ownership, usage and distribution.

In order to avoid breaching individual client’s privacy, data for the spatial distribution analysis are aggregated by geographic area. For the purpose of this report, submitting veterinarian’s postal code is used as a proxy for animal location.

Photo Caption

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Bovine BVD testing in 2015—2016: lessons learned

Report limitations

Bovine Viral Diarrhea is still a serious problem for Saskatchewan cattle industry—in 2015 and 2016 there were cases of BVD

abortions, mucosal disease, and persistent infection detected in Saskatchewan cattle. The Saskatchewan BVD screening and

control program provides support to beef producers and is a major driver for large herd testing efforts.

Samples from 46 distinct geographical locations were submitted to PDS for BVD testing in 2016 and positive results were de-

tected in five (10.8% location prevalence). In 2015, samples were received from 52 locations and positive results were found in

ten (19.2% location prevalence). While overall incidence of positive tests was only slightly lower in 2016 compared to 2015 ( 33

vs. 35 positive results), 2016 positive test prevalence rate was 25% lower (1.46% vs. 1.96%) due to much larger submission num-

bers in 2016 (2254 tests, as compared to 1788 tests in 2015). BVD case prevalence (percentage of cases whit at least one posi-

tive test result) was also lower in 2016 compared to 2015 (5.69% vs. 8.12%).

These observations must be interpreted with caution considering the short observation period (2015—2016) and potential labora-

tory submission bias.

This report is compiled from the Prairie Diagnostic Services Laboratory Information Management System (LIMS) data. Infor-

mation and analyses contained in the report are restricted by the original data quality, LIMS database design, and functional limi-

tations. The following shortcomings have been identified as of the date of this report:

The current PDS LIMS was launched on June 2, 2014. All the data collected prior to this date are stored in a separate lega-

cy database. The old and new PDS databases are operated on incompatible platforms (Cache and Microsoft SQL Server

respectively). Combining the data from these two sources is a major challenge and the main reason why this report includes

only data from the new system.

PDS, as a public animal health laboratory, serves a wide variety of clients. The main categories of PDS submissions based

on the clients’ specific needs include diagnostic investigation, research, and surveillance. The reason for submission can be

entered on a submission form but is not mandatory. Submission reason classification mechanism has been included into

PDS LIMS design, however it is not enforced. As a result, it is not possible to reliably categorize the reason for submission

data.

Poor submitters’ compliance with commodity and production stage fields on submission forms prevents reliable distinction of

beef and dairy cattle submissions as well as operation size at this time.

Premise ID can be recorded by PDS LIMS; however it is not a mandatory information field required for sample submission at

the present time. As a result, tracing sample source location using proxy data (animal owner postal code or submitting veter-

inarian postal code) adds a level of complexity and uncertainty to spatial analysis.

Similarly, the absence of Premise ID prevents clear recognition of samples submitted from the same herd at different times.

Because of the complexity of Serum Neutralization test result interpretation for diagnostic purposes, these data were exclud-

ed from some of the analyses.

A participant bias can have a potential effect on this report data as a result of individual producers and veterinarians prefer-

ences for diagnostic laboratory services usage.