PA Infectious Disease

Bio-exclusion

Activities to decrease the risk of introducing an infectious agent into a population

Bio-containment

Activities to decrease the risk of spreading an infectious agent within a population

How many targets should farmers be given when working on herd health plans

3

Scanning/passive surveillance

Data from routine clinical diagnostic work

Targeted/active surveillance

Specific data proactively collected to accurately describe disease patterns

VIDA

Veterinary Investigation Disease Analysis
Criteria that must be met for a diagnosis to be officially recorded

Limitations of scanning/passive surveillence

Bias in case submission
May not reflect real world trends

4 options for active/targeted surveillence

Compulsory testing
Random cohort tests
Import testing
High risk herd tests

Limitations of active/targeted surveillence

Must be designed for a specific condition
Will not detect new/emerging conditions

CHeCS

Cattle Health Certification Standards

Conditions included in CHeCS

BVD
IBR
Johne's
Leptospirosis
Neospora caninum

What must apply for an animal to be considered organic

It must have been born on an organic certified farm
Its mother must have been managed organically during pregnancy (full pregnancy for sheep, last 3mths for cattle)
Fed 100% organic feed

Can organic farms buy in animals

They should be managed as a closed flock but they are allowed to buy in 10% and breeding tups

Use of medicines on organic farms

Only if there is clinical justification (this includes homeopathies)
Must be authorised medicines
No use of synchonisers
Can use strategic therapy (e.g. antiparasitics)
Can vaccinate
2-3x the normal withdrawal period
Only allowed 3 courses of treatment in a year (not including anti-parasitics)

Organic farm requirement for dairy calves

Must have access to milk for 3mths

Organic farm requirements for pigs

Must have forage and outdoor access
No routine castration, tail docking, teeth clipping or iron injections

Problems with organic farming of poultry

Not allowed to clip beaks \= feather pecking is a big issue
Longer growth (x2) \= increased production costs

Problems associated with organic farming

Often poorer conformation
Variable management - good potential for better welfare and environmental impact, but often not managed well enough
Lack of veterinary input

Transmission of BVD

Direct (nasal secretions, semen, urine, milk, saliva, foetal fluids)
Mainly from PI animals

Outcome of BVD infection if animal is immune and not pregnant

Nothing/very mild transient infection

Outcome of BVD infection if animal is not immune and not pregnant

Transient infection and then immunity develops

Outcome of BVD infection if animal is immune and pregnant

Nothing/very mild transient infection
Foetus unaffected

Outcome of BVD infection if animal is not immune and is pregnant

Transient infection of cow
Foetus effect depends on stage of pregnancy

Outcome of BVD infection on the foetus in the 1st trimester (0-120d)

Abortion or PI animal

Outcome of BVD infection on the foetus in the 2nd trimester (120-240d)

Abortion or congenital defects

Outcome of BVD infection on the foetus in the 3rd trimester (240-280d)

Abortion, still birth or stunted calf

Congenital defects associated with BVD

Cerebellar hypoplasia
Ocular degeneration
Undershot jaw
Thymus/bone/growth retardation

Sources of BVD PI animals

Mainly from BVD infection of mother in 1st trimester
Born to PI mother

Will calves from a BVD PI mother always be PI animals

yes

Main source of BVD on a farm

PI animals

Antigen/antibody status of a BVD PI animal

Antigen +ve
Antibody -ve

Signs of BVD PI animal

Stunted/poor growth/DLWG
Prone to secondary infections (e.g. scour, pneumonia)
May develop mucosal disease

Mucosal disease

BVD PI animals only
Virus mutates to be cytopathic \= GI ulceration \= increased salivation and haemorrhagic diarrhoea
If one PI develops mucosal disease then it can be passed on to other PIs
Euthanise

Ddx for oral ulceration in cattle

Foot and mouth (notifiable)
Bluetongue (notifiable)
BVD/Mucosal disease
Malignant catarrhal fever
Bovine papular stomatitis
Calf diphtheria
Actinobacillosis/Wooden tongue
Actinomycosis/Lumpy jaw
Trauma
IBR

BVD infection of bulls

Transient infection affects sperm motility
Virus shed in the semen for 5mth (lifelong if PI)

Does a BVD PI bull always produce a PI calf

No, but can infect mother at mating (i.e. in first trimester) leading to a PI/abortion

Testing for BVD PI animals

Antigen tests 3 weeks apart (will both be +ve if PI) (can see false -ves in calves due to mother's antibodies)
Antibodies will always be -ve (can see false +ves in calves due to mother's antibodies)

In terms of BVD management why should pregnant cows not be bought

May be carrying a PI calf (AKA Trojan cow)

Herd testing for BVD

Screen test - sample 5 calves at 8-19m old from each management group and Ab test - tells you if there is a PI in that group
Bulk milk antibody test - old-fashioned, need 5% of herd +ve before it shows in bulk milk

How to find the BVD PI animal on a farm

Whole herd antigen testing - expensive
Can decrease the cost by testing all calves (if -ve then mothers must be -ve)

Control of BVD on farm

Remove PIs and strict biosecurity
CLosed herd if possible (esp. don't buy pregnant cows) or purchase from accredited farms and isolate
Vaccination

Scottish government BVD eradication scheme

All breeding herds must be tested
Illegal to move PIs unless to slaughter
Must make attempts to become -ve herd

Causative agent of IBR

Bovine Herpesvirus-1 (BoHV-1)

3 diseases caused by BoHV-1

Infectious bovine rhinotracheitis (IBR)
Infectious pustular vulvovaginitis (IPV)
Infectious pustular balanoposthitis (IPB)

Do all animals infected with BoHV-1 develop latent infection

yes

Transmission of BoHV-1/IBR

Nose-to-nose
Aerosol (3-5m)
Fomites
Reproductive fluids

Signs of IBR

Dull, decreased appetite
Pyrexia
Sudden milk drop
Conjunctivitis
Ocular/nasal discharge
URT signs (rapid, noisy breathing +/- cough)
+/- abortion
+/- meningitis (young animals)

Will animals show signs of a reactivated IBR infection

no (may show mild signs), but still shed

How are seronegative latent IBR carriers produced

Calf infected while still has maternally derived antibodies
Rare

Diagnosis of IBR

Ocular conjunctival swab or guarded nasopharyngeal swab for PCR
Serology (allows identification of latent animals)

Treatment of IBR

NSAIDs
Antibiotics for secondary infection
Vaccination (does not prevent latent infection but will decrease shedding and disease severity)

How are IBR vaccinated and latent animals differentiated?

Serology
Vaccinated animals will only have antibodies against gE, latently infected animals will have antibodies against gE and gB

Control of IBR in a herd

Biosecurity
Culling (not in high prevalence herds)
Isolation
Vaccination

IBR vaccine and bulls

Semen for AI must be seronegative therefore cannot vaccinate these bulls and need to be careful if using a live vaccine on farm as it can spread

Causative agent of Johne's

Mycobacterium avium subspecies paratuberculosis

How long can M. avium paratuberculosis survive in the environment

\>1y on pasture
A long time in slurry/water

Transmission of M. avium paratuberculosis/Johne's

Faecal-oral
Transplacental
Transmammary

What is the usual age of presentation of Johne's disease

3-5y

Pathophysiology of Johne's disease

Localises to GIT \= sets up chronic granulomatous enteritis \= PLE

Clinical signs of Johne's

Dairy cattle:
Milk drop and decreased fertility
Increased SCC
Decreased BCS
Beef cattle
Decreased fertility and BCS
Small, ill thriven calves
Diarrhoea
Oedema

Diagnosis of Johne's disease

History/signs
ELISA (serum/milk) - will only see after a few years
Faecal PCR/smear/culture - will only see after a few years, can be intermittent
PM/histopath

When are can false positives for Johne's be seen

Just after TB testing

Treatment of Johne's

None - isolate and cull

Can Johne's animals enter the food chain

Yes if not emaciated/oedematous or within medication withdrawal period

Control of Johne's in a herd

Biosecurity
Test and cull
Breed positive stock to terminal sire and buy in Johne's free replacements
Good hygiene at calving (and separate positive and negative animals)

Most common species of leptospirosis in UK cattle

L. Linterrogans (Hardjo)

Transmission of leptospirosis

Body fluids (esp. urine)

Signs of leptospirosis in cattle

Usually subclinical
Reproductive disease (infertility, abortion/still birth)
Milk drop with high SCC (milk may appear yellow/orange)
Pyrexia
Meningitis (

Diagnosis of leptospirosis in cattle

PCR
Serology (blood/milk)
Dark ground microscopy
Culture (difficult)
Immunofluorescence

Treatment of leptospirosis in cattle

Antibiotics
High dose PenStrep (off license)
Amoxycillin
Oxytetracycline

Control of leptospirosis in a herd

Identification and removal of carriers
Vaccination
Water hygiene

3 main types of salmonella seen in cattle

S. enterica Dublin
S. e. Mbandaka
S. e. Typhomurium

Salmonella Mbandaka

Adult cattle
Diarrhoea, malaise, abortion
From infected feedstuff
Rarely zoonotic

Salmonella Typhimurium

Mainly calves
Various signs
Carriers exist

Transmission of Salmonella Dublin

Faecal-oral
Fomites
Feed/water
Slurry

Do you get salmonella carriers?

Yes

both persistent shedders and latent infections

Clinical signs of salmonella in cattle

Wide range
Acute/chronic enteritis (pyrexia, haemorrhagic diarrhoea)
Abortion
Decreased production
Calf ill thrift/pneumonia/meningitis/septicaemia

Diagnosis of salmonella in cattle

Faecal sample
PM (esp. foetal stomach contents)
Serology

Identification of salmonella carriers in cattle

Repeated serology (3x in 8mth)

Use of antibiotics in cattle with salmonella

Should only be used if animal has septicaemia
If used for GI form it can lead to carrier status

Control of salmonella in a herd

Biosecurity
Investigation of abortion/scour/illness early on
Vaccination
Good drainage and waste management
Disinfection of calving pens
No slurry on grazed land

Snotsiekte AKA

Malignant catarrhal fever

Transmission of malignant catarrhal fever

Not transmitted cattle-to-cattle
Comes from sheep (or wildebeest)
Direct
Aerosol

Signs of malignant catarrhal fever in cattle

Dull, anorexic, pyrexic (41C)
'Head and eye' signs:
Agalactia/milk drop
Mucopurulent (+/- boody) oculo-nasal discharge
Drooling
Dyspnoea
Decreased BCS
Corneal neovascularisation, scleral congestion, hypopyon
Oral ulceration
Lymphadenopathy
Dermatitis
Cystitis
Diarrhoea

Diagnosis of malignant catarrhal fever in cattle

PCR (blood/tissue)
Serology

Treatment of malignant catarrhal fever in cattle

Euthanasia
Supportive care if very expensive animal

Control of malignant catarrhal fever in cattle

Avoid sheep around lambing (as this is when OHV-2 reactivates)

3 species of Brucella that are of greatest importance

B. abortus (cattle)
B. melitensis (goats)
B. suis (pigs)

Signs of brucellosis in livestock

Placentitis and abortion
Epididymitis and orchitis
Milk drop
Hygromas

Transmission of Brucellosis in livestock

Placental/foetal fluids, vaginal discharge
Milk
Semen (inc. AI)
Blood

Prevention of human brucellosis

Pasteurise milk
Careful handling/disposal of abortion materials
No vaccine for humans

Model for control/eradication of a disease

Phase 1 \= compulsory vaccination
Phase 2 \= restrict/ban vaccination
Phase 3 \= test and slaughter
Takes about 10y

Control of Brucellosis in livestock

Vaccination in high prevalence areas
Test and cull

Which LNs are commonly affected by bTB

Retropharyngeal
Bronchial
Mediastinal

bTB tests

SCITT - tuberculin skin test
Gamma interferon test

Scrofula

TB causing LN enlargement and difficulty swallowing

Control of bTB

Test and cull

What happens if a bTB reactor is identified on farm

Public Health notified
Herd movement restrictions
Reactors slaughtered and PMI
Epidemiological visit
Disinfection
Recently sold animals are traced
Contiguous herds tests
Herd tested every 60d and certified negative after 2 clear tests

Are mycoplasmas gram positive or negative

Positive