Bovine Leukosis: Are We Up To The Challenge

Greg Keefe DVM MSc MBAOmid Nekouei DVM

1

Introduction• Terminology

– Enzootic Bovine Leukosis (EBL) = “the disease”

– Bovine Leukemia Virus (BLV) = “the virus”• Spread

– Blood or other sources of “blood cells”– Not a free virus – needs to be in cells

• Any blood contact – Needles, dehorners, bloody trimming knives, rectal sleeves

• Also possible - colostrum, milk, reproductive procedures, in-utero (before birth) exposure

2

Introduction• Progression of Leukosis

1. Infection and development of permanent carrier state

2. Increase in circulating white blood cells – about 30% of animals develop this stage

3. Tumors – called “lymphsarcoma” in approximately 5% of animals• Superficial lymph nodes• Heart• Stomach/intestine• Spinal canal • Reproductive tract

Introduction• Diagnosis

– Mainly blood/milk antibody tests (ELISA) – Also postmortem and with a test for the virus

RNA (genetic material)• Control/eradication

– The cornerstone in all programs is preventing blood cell movement• Needles, gloves, instruments, colostrum, insects???

– Test & slaughter/segregation/biosecurity measures

– Herd conditions/goals dictate program

4

Importance• BLV can be is economically significant

– premature culling or death as a result of lymphosarcoma

– The condemnation of carcasses at slaughter– Lower production & reproductive

performance– Indirect losses: from export restrictions

• Whole countries have eradicated– UK, Denmark, Netherlands, France…..

• The prevalence in North America is increasing

5

Historic prevalence of BLV in Canada by province

7

PEI (89)

PEI Ont Que NS NB Sask Alb Man 0

20

40

60

80

100

120Animal level Herd level

1998-2003

5.5%

63%

49%

16.6%

Current BLV project• Sponsored by 3 regional boards

and AAFC (ADAPT/CAAP program)• Objectives:

– Test ability of bulk tank milk ELISA to predict prevalence

– Establish prevalence at herd level and estimate cow level

• Pave the way for herd categorization/risk assessment/ management plan similar to AJDI

9

Comparison of individual milk samples (gold standard) to

Bulk tank milk

10

General design: sampling rounds for all Maritimes dairy herds

BTM 1 BTM 2 BTM 3

BTM 4 in 90

selected herds plus all individ

ual milk

samples

11

Stratified random sampling of 90 based on

BT ELISA values (5)

641 634 628

Stratified random sampling

90 herdsNB (30)NS (30)PEI (30)

12

Based on values of BT samples from the 5

groups

Only Valacta herds

<5, 5-40, 40-55, 55-70, >70

Results from 85 herds• Manufacturers recommended cutoff of <5 = Neg• 6 herds with BT value<5 (BTM neg) in fact had a

single positive low ELISA titre animal • All negative herds were correctly classified

13

IndividualBT

- + Total

- (<5) 12 6 18+ (≥5) 0 67 67

Total 12 73 85

Relative * Sn: 91.8%* Sp: 100%

At herd-level

Prediction of within-herd prevalence by BT-values (modeling)

14

Correlation ~ 85%

With

in –h

erd

prev

alen

ce

BT ELISA values

0.1

.2.3

.4.5

.6.7

.8.9

1W

ithin

-her

d P

reva

lenc

e

0 10 20 30 40 50 60 70 80 90 100 110 120 130BT copp

ResultsBulk tank milk samples

Prevalence at herd-level

15

Overall herd prevalence• 623 herds tested 3X – 67 are <5 = negative (11%)• Can estimate within herd prevalence for the positive herds

16

020

4060

80Fr

eque

ncy

0 20 40 60 80 100mean 3 copp

A

B

C

D E BTM ELISA score and cow prevalence estimateA - < 5 = negativeB - 5 to 40 = 10%C- 40-55 = 20%D - 55-70 = 40%E - >70 = 70%

BLV take-home thoughts• BTM testing worked very well to determine

status/predict level – unfortunately........

• Prevalence of BLV infection at herd and cow levels in the Maritimes has been increased over time very high now

• We need a practical control plan for BLV

• Hence the title - Are We Up To The Challenge

17

Atlantic Healthy HerdsJohne’s Control

AJDI

Calf Mgmt and colostrum assessment

Internal parasite treatment model

BLV Control and Risk Management

BVD eradication and biosecurity

Web port - Data collection, delivery

benchmarkingLameness Mgmt.

and Benchmarking

Atlantic Healthy Herds• Cost of these diseases is $10

M/year in Atlantic Canada• Support from the 4 regional

boards• Seeking matching program

funding• Phased rollout in beginning in

2014

Thank you• Acknowledgements

– Dairy Boards– ADAPT councils– NB Dept of Ag– Valacta– MQM technical

team– Participating

farmers