86. Enzootic bovine leucosis.

Question 1

Occurrence?

Answer 1

Enzootic bovine leucosis ʹ OIE listed

• Retroviridae, Orthoretrovirinae, Deltaretrovirus, Enzootic bovine leukosis virus
• Forms of bovine leukosis: Susceptible: Bo (Ov, Cap)
• Sporadic (calf, not infectious)
• Enzootic (infectious)
• Occurrence:
• Friesian,
• worldwide,
• eradication program in several countries

Question 2

Ethiology?

Answer 2

Etiology:

• 51kD surface glycoprotein antigen
• doesnt have onc-gene, protein are responsible for the tumor formation (Rex, Tax)
• Can be cultured in bovine lymphoid cells

Question 3

Epidemiology?

Answer 3

Epidemiology:

• Horizontal infection with discharges: lymphoid cells (contact, aerogenic, PO, insemination,
• iatrogenic, insects ʹ blood also contains but not often way of transmission)
• Intrauterine (transplacental): US 4-8%, immune tolerant calves (issue for eradication) sheds but
• seronegative
• Colostrum, milk: virus + antibody
• Iatrogenic: needle, multidose injectors, rectal examination (GLOVES)
• SLOW spreading (years)
• Genetic predisposition: family cumulation, MHC-type

Question 4

Pathogenesis?

Answer 4

Pathogenesis

• Infection generally between 6 months and 3 yr old
• Target cells: B lymphocytes
• Lifelong carriage
• Three phases:
• 1) Incubation phase (1-4months): replication in lymphoid cells, seropositivity,
• asymptomatic ʹ some stay in this phase for years
• 2) Pretumor phase (2-4 yr): persistent lymphocytosis, blood smear ʹ still no CS
• 3) Tumor phase (4-5 yr): 1-10% tumor (lymphosarcoma)

Question 5

Clinical signs?

Answer 5

Clinical signs:

• Long incubation: asymptomatic
• Pretumor phase: no clinical signs, lymphocytosis, immature lymphocytes (left shift)
• Tumor phase: lymphnode enlarged (dysfunction can be caused: compress esophagus/trachea
• 2dary complications), depression, fatigue, anorexia, weight loss, drop of milk production,
• infertility Death

Question 6

Pathology?

Answer 6

Pathology:

• LN, hemopoetic tissues, tumor of lymphoreticular tissue - lymphosarcoma
• Tumor: gut, abomasum, lungs, heart, bladder

Question 7

Diagnosis?

Answer 7

Diagnosis:

• clinical signs, pathology, histology, hematology
• Detection of antibodies:
• AGP, ELISA (51kD) - blood, milk
• Persistent seropositivity
• Fluctuation: calving, vaccination (slight decrease)
• Maternal antibodies: 4-6 months
• Detection of agent:
• Detection of virus (PCR): during colostral protection, immune tolerant calves
• Virus isolation
• Differential diagnosis: sporadic leucosis (age, LN are larger), other tumor

Question 8

Prevention?

Answer 8

Prevention:

• cannot heal, removal of infected animals, close herd, restrict movement
• veterinary surgeon (sterile work, blood), colostrum/milk (pasteurisation),
• insemination with semen from disease free bulls

Question 9

Eradication?

Answer 9

Eradication

• 1) Selection: test and remove (only if lower infection, dont slaughter whole herd)
• ELISA: animals above 6 month of age, every 3-6 months
• Removal of seropositive animals
• After 4-5 tests the disease can be eradicated
• 2) Generation shift: isolation of calves within 3 days, ELISA test at the age of 6months ʹ hopefully
• seronegative
• 3) Herd replacement
• 4) Free state: 2X seronegativity 3-6 months apart, control of free state, maintaining free state