Lesson 43 - Viral Diseases of Clinical Significance in Production Animals

What would make you suspect that an animal has a viral disease?

1. fever

2. multiple members of herd affected

3. lethargy

4. high morbidity

What is a notifiable disease?

high-consequence, often foreign, diseases that must be reported immediately (typically within 24 hours) upon suspicion or confirmation to state/federal officials

What is a reportable disease?

broader, often state-defined category of infectious diseases requiring reporting to monitor or control outbreaks, which may have less urgent timelines than notifiable ones

What level are notifiable diseases on?

national/federal

What level are reportable diseases on?

state

What happens when a suspicion of a notifiable disease is reported?

immediate, urgent investigation by state or federal veterinarians

When is the classical swine fever virus vaccine used?

typically restricted to emergency outbreak situations and only under strict USDA authorization

What are the similarities between CSF and ASF?

1. spread rapidly from pig to pig

2. can be spread by feeding chilled pig meat to pigs

3. can lead to skin changes

4. can be diagnosed using RT-PCR

5. notifiable in the USA

Why is routine prophylactic vaccination for CSF prohibited in the USA?

maintain CSF free status and facilitate international trade

What kind of vaccine is the CSF vaccine?

modified live

What is an example of a state restriction of the CSF vaccine?

Texas restricts the use of modified live virus CSF vaccines unless authorized by the Texas Animal Health Commission

What is foot and mouth disease?

highly contagious viral infection affecting cattle and other cloven-hoofed animals

How many serotypes and subtypes of foot and mouth disease are there?

7 serotypes and more than 80 subtypes

What are the clinical signs of foot and mouth disease?

1. fever

2. blisters

3. painful ulcers on the mouth, tongue, teats, and hooves

How does foot and mouth disease affect production?

severe production losses such as reduced milk yield and lameness

Is foot and mouth disease a threat to human health?

no

What is required when foot and mouth disease is suspected?

immediate reporting to veterinary authorities

What should you do if you suspect african swine fever in the US?

notifiable

If the last FMD outbreak was 1929, why is it important?

1. one of the most contagious diseases of livestock

2. outbreak in the United States would have a substantial and detrimental impact on the agricultural economy

3. outbreaks in other countries have had a significant negative impact on their economies

What kind of virus is FMD?

picornavirus

What is the morbidity and mortality of FMD?

high morbidity, low mortality

What are the long-term effects of FMD?

infected animals become carriers

How does the FMDV enter the animal?

inhalation or ingestion, replicating quickly in the mucosa of the pharynx specifically within epithelial cells

Where does the FMDV go after the initial replication in the mucosa of the pharynx epithelial cells?

virus enters the bloodstream (viremia) distributing to epithelial tissues and leading to secondary replication and vesicle formation on the feet, muzzle, tongue, and teats

What does FMDV do to cells as it replicates?

it destroys them

What kind of infection does FMDV cause?

severe cytolytic with ruptured blisters and lesions within 48 hours

How is FMD diagnosed?

1. Clinical signs

2. Virus isolation/PCR of epithelial tissue

3. Antibody detection on blood - ELISA

How is FMD treated?

cull

Is there a FMD vaccine?

no

What is the preferred method of FMD prevention?

eradication

What are the differentials for FMD?

1. vesicular stomatitis

2. blue tongue

3. infectious bovine rhinotracheatis

What is essential for FMD prevention?

border monitoring for disease

What kind of virus is bovine leukemia virus?

lentivirus

What kind of virus is maedi visna/OPP?

lentivirus

What disease is caused by bovine leukemia virus (BLV)?

Enzootic Bovine Leukosis (EBL)

What is Enzootic Bovine Leukosis (EBL)?

blood-borne disease

What cells are affected by the bovine leukemia virus?

white blood cells

What percent of cows infected with BLV develop clinical disease?

5%

What is the state of BLV in the US?

highly endemic in the United States, infecting approximately 94% of dairy herds and roughly 40-50% of individual dairy cows, with a significant presence in beef cattle

What is the primary clinical sign of BLV?

tumors (lymphosarcoma) in the uterus, abomasum, heart, spinal canal, and/or lymphoid tissue behind the eye (which makes the eyeball protrude)

What is another symptom of BLV?

most, or all, internal lymph nodes enlarge and become readily apparent under the skin

How do most cows with BLV present?

no signs of the disease and the infection does not appear to affect their milk production or any other functions

What happens when clinical signs of BLV are present at slaughter?

condemn carcasses

How is BLV diagnosed?

1. clinical signs

2. ELISA

3. semen testing

What does a positive ELISA for BLV mean?

disease positive because there is no vaccine

How is BLV prevented?

1. properly discard needles and syringes

2. use blood-free syringes to pull up drugs

3. wash and disinfect instruments

4. use an electric dehorner instead of gouge or saw because they are hard to clean

5. test and cull

6. feed colostrum from negative cows in low prevalence herds

7. feed frozen colostrum in high prevalence herds

8. clean calving pens

9. test all incoming animals

How can we determine if a calf coming from a BLV positive mom has been infected in utero?

BLV antibody ELISA prior to giving colostrum

What kind of virus is bovine immunodeficiency virus (BIV)?

lentivirus

What kind of herds is BIV infection more common in?

higher in dairy herds compared with beef cattle

What is the suspected mode of transmission of BIV?

1. horizontal transmission in body fluids such as blood, milk, semen, and colostrum

2. vertical transmission through natural transplacental infection

Is there a commercial test for BIV in the US?

no

What are the target species for malignant catarrhal fever (MCF)?

cattle, American bison, water buffalo, and various deer species

How is MCF spread?

1. from asymptomatic carrier species (specifically sheep, goats, or wildebeest) to susceptible animals

2. generally not transmitted between affected cattle

What is the preclinical phase of MCF?

lymphoid tissue infection

What is the pathogenesis of lymphoid tissue infection with MCF?

1. explosive proliferation of lymphocytes, especially CD8+ T cells, which infiltrate multiple organs and the vascular system (vasculitis)

2. widespread tissue damage is thought to be mediated by this aberrant immune response and vasculitis

3. necrosis of mucosal surfaces, severe inflammation, and organ failure

When do symptoms of MCF usually appear?

5-10 days before death

What are the clinical signs of MCF?

1. high fever, severe depression, anorexia

2. corneal opacity (often starting at the edge)

3. mucopurulent discharge

4. mucosal erosions

5. neurological signs

How is MCF diagnosed?

1. clinical signs

2. PCR

How is MCF prevented?

1. preventing contact between susceptible species (cattle/bison) and carrier species (sheep/goats), especially during lambing/birthing

2. no vaccine

What is the federal status of MCF?

reportable

Does MCF pose a threat to human health?

no

What is epizootic hemorrhagic diarrhea?

a disease of wild ruminants, particularly white-tailed deer in North America that is clinically seen in cattle, not small ruminants

Does true persistent infection of EHD happen in ruminants?

no

How does EHD present in sheep?

can be infected experimentally but rarely develop clinical signs

How is EHD transmitted?

1. culicoides biting midges

2. viraemia can be prolonged beyond 50 days

3. deer can be viraemic for up to 60 days

4. not known to cause disease in humans

What are the clinical signs of EDH in deer?

1. Fever, weakness, inappetence

2. Excessive salivation

3. Facial edema

4. Hyperemia of the conjunctiva and mucous membranes of the oral cavity

5. Coronitis

6. Excessive bleeding from bloody diarrhea and hematuria

7. Dehydration

8. Death

What are the clinical signs of EDH in cattle?

1. Fever, anorexia, reduced milk

2. Swollen conjunctiva, redness and scaling of the nose and lips, nasal and ocular discharge, stomatitis, salivation, swelling of the tongue, oral/nasal erosions

3. Lameness, and dyspnoea

4. Abortions and stillbirths

5. Death in some cases

What are the ddx of EDH in deer?

1. indistinguishable from Bluetongue

2. foot and mouth disease

What are the ddx of EDH in cattle?

bluetongue, bovine viral diarrhoea, foot and mouth disease, infectious bovine rhinotracheitis, vesicular stomatitis, malignant catarrhal fever, and bovine ephemeral fever

What are the clinical signs of rinderpest in cattle?

1. acute fever

2. ocular and nasal discharge

3. necrotic stomatitis

4. severe gastroenteritis

What kind of virus is rinderpest?

morbillivirus

What is the pathogenesis of rinderpest?

replicated in the lymphatic system before attacking the gastrointestinal and respiratory mucosa

How is rinderpest spread?

1. direct contact

2. contaminated water

3. aerosolization

What is the global status of rinderpest?

eradicated

What are the goals of a pig herd health plan?

1. disease prevention and control

2. improving productivity and profitability

3. monitoring and evaluation

4. ensuring welfare and compliance

5. systematic approach

How can pig health be optimized?

1. appropriate feeding

2. health checks for early detection and isolation

3. testing

4. vaccines

5. making sure treatments are working

6. quarantine

7. housing, ventilation, drainage, age grouping

8. all in, all out

9. colostrum protocols

How can diseases be monitored in pigs?

1. Record

2. Feed conversion rates/weight gains per day or week

3. Age to finishing

4. Number of piglets/sow

5. Conceptions/services

6. Deaths

7. Antibiotic use

8. Post mortems

9 Testing

10. Feed and water intake

How can disease spread be minimized in pigs?

1. Early detection

2. Isolation

3. Biosecurity

4. Airflow

5. Waste flow

6. Pest control

7. Slaughter

8. Vaccination

9. Reduce stress

10. Lower stocking density

11. Dispose of dead pigs asap

12. Prophylaxis vs metaphylaxis

How can we prevent bringing disease to a pig farm?

1. Quarantine

2. Buy from known source

3. No showing

4. A.I. (instead of buying boars in)

5. Vaccinate

6. Testing

7. Vermin and bird control

8. Remove diseased animals

9. Dip in/dip out

10. Wear different clothing in each pen

11. Secure barriers/fencing

12. No feeding waste food

13. Effective disinfectants for fomites