Gerald L. Stokka et al., Bovine Leukosis, Kansas State University, November 1998

Falkner, Thomas R.

Shirley, John E.

Smith, John F., 1962-

Stokka, Gerald L.

Van Anne, Travis

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1Bovine LeukosisGerald L. Stokka, Extension BeefVeterinarian, Animal Sciences and IndustryJohn F. Smith, Extension Specialist,Animal Sciences and IndustryJohn Shirley, Associate Professor,Animal Sciences and IndustryThomas R. Falkner, Extension Assistant,Animal Sciences and IndustryTravis Van Anne, Veterinary Student,College of Veterinary MedicineKansas State UniversityAgricultural Experiment Station andCooperative Extension ServiceBovine leukosis usuallydevelops in organs or lymphnodes and is not expresseduntil adulthood.Cattle with the adult(enzootic) form of bovineleukosis are usually 4 years ofage or older, but the diseasecan occur as early as 2 yearsof age.BLV cows may be culledbecause of poor milk produc-tion that, in some instances,results from poor appetiteand weight loss. Poor appetitemay be attributable to neo-plastic growths in the pharyn-geal area, which inhibit theability to swallow.Other signs of the diseasevary. Affected cows may bediagnosed as having suchproblems as traumaticreticuloperitonitis/reticulopericarditis, abomasalproblems, and spinal cordlesions, especially thoseaffecting the rear legs.Abortions and infertilityalso may occur if the uterusor other reproductive organsare affected.Diagnosis and Trans-missionRectal palpation is the bestdiagnostic tool to locateinternal tumors if peripherallymph node enlargement orexophthalmos is not ob-served.Using the agar gel immun-odiffusion (AGID) test, BLV-infected cattle can be identi-fied by testing sera for BLVantibodies. The virus oftenremains dormant in infectedcows until they are stressed,such as during extremely hotor cold weather, parturition,or illness. Clinical signs areapparent in BLV-infectedcattle less than 1 percent ofthe time. However, thenumber of cows condemnedat slaughter plants is on therise, suggesting that thenumber of infected cows isincreasing nationally.The virus is usuallytransmitted through contactwith the blood of an infectedanimal. Only 0.0005 milliliterof blood is needed for thevirus to infect the lympho-cytes of healthy animals.BLV can spread throughsuch procedures as infections,castration, dehorning, andrectal palpation, as well asthrough insect vectors, suchas horseflies. Balling guns, orany instrument that comes incontact with cattle, should besanitized properly after eachuse. Breeding by naturalservice may also be a sourceof infection because bloodmay be transferred duringcopulation.The calves of infected damsbecome infected with thevirus at birth about 5 percentof the time.In addition, calves fed BLV-positive milk have a greaterrisk of contracting the infec-tion. Cows with a high virusload and low antibody titermay transmit infection totheir offspring, whereas cowsexhibiting a low virus loadand high antibody titer aremore likely to transfer immu-nity to their offspring. Thisimmunity is only temporary,Bovine leukosis, bovine leukemia, lymphosarcoma, andmalignant lymphoma are all names given to the retrovirusdisease caused by bovine leukosis virus (BLV) in cattle. All ofthese terms refer to a neoplastic condition of tissues thataffects lymph nodes and lymphocytes. True leukemias, inwhich the entire body is affected, are rare.Outdated Publication, for historical use. CAUTION: Recommendations in this publication may be obsolete.2however, as it results fromcolostral antibodies that lastjust a few months.To date, little evidenceexists that BLV is transmis-sible to humans. Pasteuriza-tion destroys the virus easily,and it can live only a fewhours at room temperatureoutside of living cells.Families that consumedraw milk containing the viruswere studied and found to befree of BLV infection.In addition, veterinariansand others who work closelywith BLV-positive blood on adaily basis have not beeninfected.Economic LossesBreeders of purebredssuffer the biggest economiclosses if their cattle are foundto be BLV-positive. Manycountries and U.S. companieswill not accept animals oranimal products infected withBLV. Heifers or semen may berejected, resulting in a largemonetary loss to the breeder.Some countries also requireembryo-producing dams tobe seronegative. The eco-nomic impact to commercialdairy producers includestreatment and diagnosticcosts, reduced performance,on-farm death losses, con-demned carcasses, and cost ofreplacements.Prevalence in U.S.DairiesThe number of cows in theUnited States condemned atslaughter because of lymphnode tumors(lymphoasrcomas) tripledbetween 1975 and 1990 and isnow nine times that of whatDenmark was during the1950s (before leukosis controland eradication programs hadbegun).It has been suggested thatless than 2 percent of infectedcows will develop lymphosar-coma in a typical dairyoperation each year.The total number of U.S.animals infected with BLVhas not been determined;however, in a study of theupper midwest states duringthe 1970s, approximately 20percent of cows were esti-mated to be infected.In 1984, some states,including Wisconsin (22.2percent), Florida (47.7 per-cent, and Michigan (30percent) reported the preva-lence of BLV-infected dairycattle. Beef cows had lowerinfection rates, ranging from0.12 percent to 6.7 percent.More recent informationindicates that 89 percent ofU.S. dairy operations containBLV-positive cattle.The increasing number ofcondemned carcasses sug-gests that the current manage-ment of dairy cows is notpreventing additional BLVinfections. Although BLV isnot easily spread from animalto animal, increasing animaldensity per pen and exposureto blood increase the risk oftransmission.Calf management prac-tices, such as gouge dehorn-ing, ear tagging, and brand-ing, can contaminate feedareas and other facilities withblood.Multiple use of the sameneedle during routine vacci-nations, use of unsterilizedneedles, and not changinggloves during insemination orpregnancy testing can alsoincrease the number of BLV-positive animals.Establishing an Elimina-tion ProgramBecause no BLV vaccine isavailable, establishing newmanagement and veterinarypractices is the key to control-ling the disease (see Recom-mendations for Reducing BLVTransmission). The first stepis blood testing, which allowsBLV-positive animals to beidentified and groupedseparately.The serologic test ofanimals younger than 6months of age may showfalse-positive results becauseof the presence of colostralantibodies. Pregnant animalsshould be serotested at least 6weeks before parturition toprevent false-negatives,which result from immuno-globulins shifting to colos-trum.Simply separating infectedanimals will reduce incidencewhen older BLV-positivecows are replaced by BLV-negative heifers.Complete eradicationprograms should be imple-mented by dairies that sellheifers, embryos, or semen sothey can achieve BLV-freestatus for their herds. Onlyone state, New York, hascertification programs toidentify BLV-free dairy herds.Proposals for controlinclude:• Identifying sick animalsthrough regular bloodtesting.• Establishing practices andprocedures to prevent thetransfer of blood or otherfluids from BLV-positive toBLV-negative animals.• Isolating infected fromnoninfected animals.• Increasing culling ratesmay also help to rid theherd of BLV-positive cowsmore quickly and to reduceexposure of healthyanimals.Outdated Publication, for historical use. CAUTION: Recommendations in this publication may be obsolete.3Recommendationsfor reducing BLVtransmission• Use only single-use dispos-able needles and palpationsleeves and then discard.• Thoroughly clean allsurgical instruments thatcome into contact withblood, such as those fordehorning, castration, extrateat removal, tagging, andtattooing.• Disinfect instrumentsbetween uses.• Reduce numbers of bitinginsects• Test all cattle entering theherd for BLV, and isolatethem for 30 to 60 days. Testagain at the end of theisolation period.• Implement annual testingfor all animals. A 3- to 4-month testing interval ispreferred but may beimpractical.• Use BLV-negative bulls orsemen for all breedings.• Do not use colostrum ormilk from BLV-positivecows. Feed calves milkreplacer or pasteurizedmilk when BLV-free milk isnot available.• Store intravenous tubingand needles in a disinfec-tant solution, such aschlorhexidine.• Cold sterilize calf deliveryequipment between uses.• Do not use BLV-positivecows as recipients forembryo transfer. If a highlyvaluable donor is testedpositive, implant embryosin BLV-negative cows andtest the offspring of thedonor to be sure they areBLV-free.• Remove extra teats, insertear tags, and dehorn whilecalves are housed indi-vidually.• Use bloodless dehorningmethods, such as electric,hot iron, or caustic paste.• Clean feed and watercontainers regularly toreduce blood contamina-tion.• Perform all veterinaryprocedures on BLV-positivecows last.• Milk all BLV-positive cowslast.Miller J: Personal communi-cation, USDA, NationalAnimal Disease Center, Ames,IA, 1996.Whittier D: Programs canrid herds of bovine leukosis.Hoard's Dairyman 138(8):405,1990.Johnson R, Kaneene JB:Bovine leukosis is caused by avirus. Hoard's Dairyman129(11):716-717, 1984.Smith B: Large animalinternal medicine, ed 2. StLouis, Mosby-year book,1996, p 1238.Howard T: Is bovine leukosisout of control? Hoard's Dairy-man 137(14)571, 1992.Samagh BS, Kellar JA:Seroepidemiological survey ofbovine leukaemia virus infectionin Canadian cattle, in StraubOC (ed): Current Topics inVeterinary Medicine andAnimal Science, Vol.15._____1980, pp 397-411.High prevalence of BLV inU.S. dairy herds. USDA,APHIS, VS, NAHMS228:197,1997.Johnson R, Kaneene JB:Bovine leukemia virus. Part IV.Economic impact and controlmeasures. Compend ContinEduc Pract Vet 13(11):1727-1737, 1991.McGinnis CW: Bovineleukosis control. Dairy briefs(Cooperative ExtensionService, University of NewHampshire) 32(1):8, 1987.Outdated Publication, for historical use. CAUTION: Recommendations in this publication may be obsolete.4Brand names appearing in this publication are for identification purposes only. No endorsement is intended,nor is criticism implied of others not mentioned.Publications from Kansas State University are available on the World Wide Web at: http://www.oznet.ksu.eduContents of this publication may be freely reproduced for educational purposes. All other rights reserved. In each case, creditGerald L. Stokka, Robin Falkner, Patrick Bierman, Bovine Leukosis, Kansas State University, November 1998.Kansas State University Agricultural Experiment Station and Cooperative Extension ServiceEP-51 November 1998It is the policy of Kansas State University Agricultural Experiment Station and Cooperative Extension Service that all persons shall have equal opportu-nity and access to its educational programs, services, activities, and materials without regard to race, color, religion, national origin, sex, age or disability.Kansas State University is an equal opportunity organization. Issued in furtherance of Cooperative Extension Work, Acts of May 8 and June 30, 1914, asamended. Kansas State University, County Extension Councils, Extension Districts, and United States Department of Agriculture Cooperating, Marc A.Johnson, Director.Outdated Publication, for historical use. CAUTION: Recommendations in this publication may be obsolete.

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