NATIONAL BVD CONTROL PROGRAMME

Transcription

1 NATIONAL BVD CONTROL PROGRAMME LECTURE FOR AHDA conference [29/01/2014] [C S Parker BVM&S DBR MRCVS] [l] Royal Veterinary College

2 National BVD control programme with thanks to Joe Brownlie, RVC How your business can interact with the national BVD control programme

3 What is BVD? An RNA virus a pestivirus Enveloped Has two different biotypes (a) non-cytopathic (b) cytopathic Has mutational changes in field viruses (genotypes) Is widespread both nationally and globally

4 The main PESTIVIRUSES Classical swine fever virus (Hog cholera virus) Bovine virus diarrhoea virus Border disease virus Are they important?

5 Back to BVD BVD research & control:- Farmers / Vet perceptions Virus & Disease European status Control and eradication

6 Pieces that need to be in place to combat BVD Education

7 Farmers said that their Vet was the main source of information on infectious disease Q9 What are your sources of information on infectious diseases in cattle. Let's start with your main source?

8 Total virus count Mean Antibody Level (ELISA units/ml) BVD virus : acute infection and immunity Natural infection with BVD virus gives immunity to re-infection Nasal shedding Viraemia Serology Time post infection (days) 0

9 Group 1 ACUTE INFECTION - mild disease >90% UK herds BVDv nc - virus clearance days - antibody responses slow weeks - long immunity but possibly not life-long

10 ACUTE INFECTIONS

11 BVD immuno-suppressive with mixed infections Respiratory infections Worse with BVDv! BVDv + other viruses (IBR+RSV) +bacteria (M. Haemolytica) Enteric infections Worse with BVDv! BVDv + other viruses (corona & rota) +bacteria (Salmonella etc)

12 Group 2 ACUTE INFECTION - severe disease often fatal - virus clearance days BVDV nc - thrombocytopenia, diarrhoea, haemorrhagic disease - weak cross-protection to Group 1 BVDV antibodies - distinct 5 UTR clustering

13 Reproductive disease

14 BVDV - effects on pregnancy Sero-positive calf Persistent Infection Congenital defects Early embryonic death Foetal death, abortion and Mummification Months of gestation

15 Persistently infected (PI) calves 1-2% of national population (Houe 1999) In a study of BVDV in SW UK, 59% herds infected (Booth & Brownlie 2012) 80% infected herds contained PI animals 0.3% 3% PI animals in infected herds (Booth & Brownlie 2012)

16 nc BVDv in early pregnancy Birth of a PI calf Cow and calf infected Only dam becomes immune Calf born persistently infected (PI)

17 PI animals Early pregnancy (up to 110 days) early foetal loss, persistently infected animals 1-2% of national population are PI animals These PI animals are viral super-shedders and the main reservoir in cattle

18 Transmission pathways PI dam always produces PI calf 100% How often does acute infection in pregnant dam result in PI calf the Holsteins go on Holiday? (see next slide)

19 Pathways to produce PI calves? PI dams to PI calf 7% Acute infection in non- PI dam to produce PI calf the Holsteins go on Holiday 93%

20 BVDv Infection during very early pregnancy (Days 1-24) Early Embryonic Mortality In 2 large scale experiments, pregnancy rate was reduced from:- about 80% (un-infected) to about 30% or lower (BVD infected) (Virakul 1988) (McGowan 1993)

21 Age (Years) Ages of PI Animals Identified in BVDvinfected herds Farm Number - PI Number Note that 28% were 2 years or older! Booth and Brownlie 2012

22 Mucosal disease MD Fatal, usually in animals older than 6 months Oral/intestinal erosions esp. Peyer s patches Lymphoid destruction

23 nc BVDv Mucosal Disease in early pregnancy Cow and calf infected Only dam becomes immune Superinfection with BVDv cytopathic biotype Calf born persistently infected (PI) Fatal Mucosal disease

24 Pieces that need to be in place.. Motivation Education Vets are main motivators of BVDv control!

25 The costs of BVD infection?

26 Costs of Disease IBR 6 million/year (Range 5.2-7) Johnes 0.8 million/year (Range ) Leptospirosis 11 million/year (Range ) BVD 39.6 million/year (Range ) (An Economic Assessment of Livestock Diseases in Great Britain Bennett & IJpelaar (2003), University of Reading)

27 Pieces that need to be in place.. Motivation Good diagnostics Education

28 Common Laboratory Tests For BVD virus Diagnosis and Testing

29 Laboratory Tests - (Hunting the PI!) 1. Antibody ELISA (Milk/Blood) 2. Antigen ELISA 3. Ear Notch Antigen ELISA 4. Polymerase Chain Reaction PCR (Milk/Blood)

30 Antibody ELISA Indicates Exposure to disease Blood (clotted/heparinised) Use to screen likelihood of BVDV on farm Young stock cohorts Bulk Milk (see next slide) Don t forget PI = Ab negative! SHOULD NOT BE USED ON ANIMALS UNDER 6 MONTHS

31 Bulk Milk Antibody ELISA Indicates Exposure of the milking herd Longitudinal tests needed Mid/low positive may actually be an increasing titre Historic infection Individual Ab remains high for years after infection Youngstock tests more use? Vaccination effects

32 Antigen ELISA Use to identify viraemic animals (mainly PI s) Blood/Tissue Sample May, occasionally, pick up acute infection retest positives 3-4 weeks later Age at testing Not under 30 days for blood Down to birth for tissue

33 Ear Notch ELISA Use to identify viraemic animals Ear Notch Tag/Notcher Identify PIs May pick up acute infection retest positives 3-4 weeks later (confirm positive with second Ag ELISA)

34 Polymerase Chain Reaction (PCR) Use to identify viraemic animals Blood/Milk sample Acute infection (50days)/PI Use on all animals (inc <30 days) CONTAMINATION

35 Bulk Milk PCR Sensitive to detect 1 PI in 300 contributors Only tests the milking animals Dry/Abx/Fresh calvers need testing separately Herds >300 milking animals 2 tests over 2 days, reverse milking order?? CONTAMINATION

36 Pooled Blood PCR Blood samples pooled in groups of ten animals Acute infection and PI Re-test animals in positive pools with Ag ELISA CONTAMINATION

37 What are the chances of PI in an infected herd? in practice, a herd is not infected until one or more PIs have been established BVDV cannot persist in a herd where contacts between PI animals and susceptible animals in early pregnancy do not occur (Lindberg et al 1999) Lindberg, A. L. E., Alenius, S., (1999) Prin Veterinary Microbiology 64,

38 Approaching BVD Control on Farm

39 BVD Control Options GB Do Nothing Vaccinate Control PI calves Control PI calves & Vaccinate European programmes with no vaccination!

40 Vaccinate 1. Primary course before 1 st service 2. Booster vaccination BVD Virus

41 Vaccination = key factor in the control & prevention of infectious disease - VETS Vaccination Biosecurity advice Testing Blood Testing Monitor performance characteristics Diagnosis Herd Health Plan Milk Testing Isolation Cull infected animals Promote routine herd visits by the vet Stock purchase control/close herd Herd health Other (<=2 mentions) 12% 11% 10% 10% 6% 5% 5% 5% 3% 9% 26% 37% 45% Culling PI is critical for control! 77% 0% 10% 20% 30% 40% 50% 60% 70% 80%

42 Non-Systematic Approach Involving Vaccination What can 40 years of vaccination and 160 currently licensed vaccines* do to eradicate a disease? When you are talking about bovine viral diarrhea virus, apparently not much it is still thriving. Although applied almost world-wide, just unsystematically vaccinating cattle does not even influence the high incidence (in cattle populations) of BVDV infections * in the USA ** J. Ridpath, 2002:

43 So, BVD Vaccines are only as good as they are correctly used to authorised data sheets! In USA study 376 Farms surveyed 82% Producers use a BVD Vaccine BUT ONLY 27% of these farms used it correctly

44 Use and Misuse of BVD Vaccine in the Field 71 farmers interviewed who use BVD vaccine regularly (60 dairy, 11 beef) 34% never referred to the datasheet 21% applied the wrong dose or route of administration All farms gave two doses as the primary course, BUT 48% administered doses at an incorrect interval 24% completed the primary course at an appropriate stage prior to service Only 7% considered concurrent disease as a reason to postpone vaccination 100% of farmers using Vaccine A administered boosters at incorrect intervals Meadows D (2010) A study to investigate the use and application of BVDV vaccine in UK cattle. Cattle Practice

45 Use and Misuse of BVD Vaccine in the Field Common on farm mistakes No universal system for transport of vaccine Storage on farm, the fridge! Checking the Fridge temp Making up the vaccine Injecting the vaccine- 1) Site 2) Route 3) Sterility

46 What Happens if you vaccinate the following herds!

47 Herds..with PI??

48 Herds. with immune cows (PI removed or vaccination?) BM Ab

49 Herds. but naïve (closed herds?) Acute infection in a herd??

50 What is happening in Europe?

51 BVD in Orkney George Baikie (Regional Manager SAC) Having eradicated BVD from Orkneys, farmers have:- 3 to 4 more calves per farm (av. herd size about 60) less barren cows less abortions more and bigger cattle.. in fact, farmers are complaining that their sheds are no longer big enough to winter house their stock

52 National Regional

53 Norway Sweden Denmark Finland

54 Austria Switzerland Germany

55 Biosecurity Identifying greatest risks PI animals on farm Introducing PI animals to farm Bulls (PI animal, pregnant animals, bulls) From neighbours cattle Acute (transitory) infections Bleeding, embryo transfer, fomites etc

56 Pieces that need to be in place.. Motivation Sufficient resources Education Good diagnostics Ownership strategy

57 Successful disease control? Are there any common themes in the national European programmes for controlling (and eradicating!) BVD? A national strategy and leadership Usually a common technology for identifying PI animals Central surveillance and monitoring Strong educational programmes Adequate funding and resources

58 National Schemes in UK & Ireland Scotland Ireland England Wales

59 New Initiative for England Industry Backing for the Initiative: - CHAWG, DairyCo, Eblex and RDPE (Defra)

60 BVDV Control Summary arguably the singly most important endemic pathogen of cattle in developed countries Most important principals of control are:- Education Biosecurity Commitment Strategic planning