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What is the cause of sporadic bovine leukosis?

Cause is unknown and affected cattle are seronegative for the EBL virus.


What clinical signs are seen in the juvenile form of sporadic bovine leukosis?

occurs in calves 2weeks -6months, characterised by generalised enlargement of all lymph nodes. superficial LNs are visinble form a distance and gradual weight loss, depression and other signs related to tumour masses in thorax and abdomen.


What clinical signs are seen in the thymic form of sporadic bovine leukosis?

Occurs in older cattle typically 1-2 years of age. characterised by massive enlargement of the thymus and local LNs. thymic mass causes jugular engorgement, oedema of brisket extending to submandibular region and chronic bloat due to oesophageal compression.


What type of virus is BVD?

A pestivirus closely related to viruses causing border disease in sheep and classical swine fever in pigs.


What are the two types of BVD virus?

Cytopathic virus
Non cytopathic virus.
There is also two pathogenic genotypes type 1 and 2 BVDV, BVD-2 mainly is present in the USA.


How is BVD virus shed?

Viraemic animals shed virus in nasopharyngeal secretions, urine and aerosol droplets. Faeces is not a major source of virus excretion. Sheep and deer can also act as vectors of the virus, causing infection of cattle but this is low risk. Virus can also be transmitted in fresh or frozen semen of infected bulls and via embryos.


When does acute BVDV infection occur?

Seen when a previously unexposed antibody negative animal becomes exposed to non cytopathic BVD virus. Following transient viraemia the animal seroconverts within 3-4 weeks and may remain antibody positive for years. Many infections are subclinical.


What are the clinical signs of acute BVDV infection?

Many are subclinical. Signs include pyrexia, leucopaenia, dullness, oral nasal eroions which quickly heal, transient scour, milk drop. most affected animals recover uneventfully. May temporarily lower immunity to other infectious diseases e.g salmonella, ibr, rsv, coccidia.


What are the sequelae to acute bvdv infection in a pregnant animal?

Acute BVD infection during pregnancy in a naive cow/heifer can cause various problems associated with transplacental infection of the foetus in utero. Depending on stage of pregnancy can get embryonic death, feotal abortion /death, mummification, congenital defect of CNS/eye, weak/premature calves, live persistently viraemic calves or live normal seropositive calves.


What is the sequelae when a cow is infected with BVD when

May lead to the birth of a live persistently infected calf. this is caused by failure of the foetus to recognise virus as foreign due to immune system not being fully functional


What is the sequelae when a cow is infected around 90-150 days of gestation?

May lead to congenital abnormalities forming cataracts, retinal dysplasia, cerebellar hypoplasia, CNS dysmyelination, cerebral cavitation. These calves are normally antibody positive if sampled before sucking colostrum.


What happens if a cow is infected with BVD >150 days of gestation?

Often gives live seropositive calves born at full term. Abortion can occur following infection at any stage of pregnancy but is not common.


when do maternally derived antibodies normally dissapear?

They normally disappear in calves by 6 months but can persist for as long as one year.


How does mucosal disease occur in calves?

Can only occur in animals which have been born persistently viraemic following in utero exposure to Nvp BVD in early pregnancy. Mucosal disease occurs when a PI animal becomes superinfected with CpBVD virus. This can occur from genetic assortment within PI animal or from a new strain or assortment of a heterologous strain to the NCP BVD strain. Most cases occur in 6 months to 2 year age group which may coincide with the waning of passive immunity. Most PI animals die within the first two years of life but a few can survive until much older.


What are the clinical signs of mucosal disease?

Acute onset depression, pyrexia, anorexia. Salivation around muzzle, widespread oral/nasal erosions/ulcers especially on the hard palate, gums, dental pad. Often muco purulent nasal discharge. Profuse diarrhoea/dysentry with shreds of gut mucosa/blood present in terminal stages.


How can acute BVD infection be diagnosed?

Paired acute/ convalescent sera 3-4 weeks apart to demonstrate rising titre (ELISA) hard to interpret in calves


How can mucosal disease be diagnosed?

Characteristic PM findings - virus isolation from pm tissues. Take blood sample and test for antibody/antigen. Normally antibody negative, antigen positive on ELISA test. May be low antibody titre along with virus positive due to persistent maternally derived antibodies.


How can PI calves be diagnosed?

can often be clinically normal before developing mucosal disease but may commonly be presented as chronic ill thriven or stunted calves. Can confirm PI status by testing tissue (ear notch) or blood for persistent viraemia. Ear notch testing can be done at any age. IDEXX BVDV serum antigen test used by some labs appears to accurately detect PI calves from 1 month of age in the presence of maternal antibodies. Take two samples 3-4 weeks apart to confirm persistent virus positive status.


What is the treatment for BVD?

In acute BVD- symptomatic supportive treatment for enteritis.
Mucosal disease - no effective treatment, will invariably die.
Persistent infection - should be disposed of as act as a source of infection.


How can vaccination be used for BVD?

Initial vaccine 2 doses 3-4 weeks apart before first service followed by boosters at 6 or 12 month intervals depending on the vaccine used. if all breeding females are vaccinated then this should control disease by preventing acute BVD and production of PI calves.


How can BVD be eradicated?

By whole herd blood testing and elimination of PI carrier animals. Strict biosecurity measures must be maintained to prevent reintroduction of disease as herd will soon become naive.


What age group of calves is necrotic enteritis most commonly seen in?

Spring born suckled calves and normally affects calves 2-4 months old. Most cases are seen at pasture in june/july.


What are the clinical signs of necrotic enteritis?

Depression and pyrexia in acute stages, diarrhoea often profuse and haemorrhagic then progressing to more scant muco haemorrhagic faeces, tenesmus, abdominal pain, pale mm membranes, occasional oral and nasal ulcers. death in 7-10 days.


What clinical chemistry findings would be present in a calf with necrotic enteritis?

anaemia, leucopaenia caused by a severe non regenerative neutropaenia. Cases exhibiting profound neutropenia carry a poor prognosis.


What gross pathology is seen in calves with necrotic enteritis?

Crusting of nasal mucosa with oral ulceration occasionally seen. Ulcers are often overlaid by necrotic debri and secondary fungal infection. Ileum, caecum and colon are areas most commonly affected with lesions sometimes extending as far as the rectum. The ulcerative lesions vary from small discrete punctate lesions to large linear diptheritic placques overlying peyers patches.


What is the treatment for necrotic enteritis?

No specific aetiological agent has been identified so the treatment is symptomatic - sulphonamides, IV or oral fluid therapy, multivitamins.


What are the most common types of salmonella serovars that infect UK cattle?

S typhimurium and S dublin. S typhimurium is a zoontoic risk.


How is salmonellosis spread?

Faecal oral infection is the most common route of infection. S dublin infection normally arises form exposure to infected puchased animal or from carrier animals in herd. In infected herds cows can become symptomless carriers and excrete at times of stress. S typhimurium infection also normally arises due to contact with infected purchased animals, or via contaminated feedstuffs, pasture or water courses.


When do most outbreaks of salmonellosis occur?

during the winter months


What are the clinical signs of salmonellosis in calves?

Often 2-6 week old calves affected, can be acute septicaemia and death with either serotype, S dublin may cause pneumonia, commonly dull, anorexic, pyrexic and have pasty faeces with blood present, develop more watery foul smelling diarrhoea with shreds of gut lining passed. Progressive dehydration with tucked up abdomen.