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Brucellosis

ISSN 2398-2993

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Synonym(s): zoonosis zoonotic prregnacy

Introduction

  • Cause: bacteria from genus Brucella; it is mainly Brucella abortus that causes disease in cattle, but in some regions, Brucella melitensis is the main causal agent.
  • Brucella suis has occasionally been isolated from cattle but does not appear to cause disease or be spread between individuals.
  • Signs: reproductive failure: abortion, premature calvings, reduced milk production, reduced weight gain
  • Diagnosis: serology, culture of bacterium from milk or vaginal swab.
  • Treatment: legislation and eradication policies in many countries means that treatment is often forbidden. In those countries where treatment is allowed, oxytetracycline and streptomycin may be considered.
  • Prognosis: dam lives and will go on to have live offspring but may keep shedding the bacteria.

Presenting signs

  • Contagious disease of cattle causing abortion in late pregnancy.
  • Abortion storm.
  • Premature calvings (<271 days gestation), stillbirth.
  • Retained placenta and metritis.
  • Infertility.
  • Less commonly mastitis, orchitis and ocular disease.

Geographic incidence

  • Eradicated from the UK in 1979:
    • UK declared officially ‘Brucellosis free’ in 1985. However, this status has been broached on several occasions by imported cattle, the latest of which was 2004.
    • Northern Ireland was declared officially Brucellosis free (OBF) much later, on 6th October 2015.
  • Other countries are ‘Brucella free’: West and North Europe, Canada, Japan, Australia, New Zealand.
  • Disease is still endemic in many countries: Middle East, Mediterranean, sub-Saharan Africa, South East Asia, with India, Peru, Mexico having the highest incidence.
  • Brucellosis is an endemic zoonotic disease in most of the developing world.
The World Health Organization (WHO) have classified it as one of the world’s leading 'neglected zoonotic diseases'.

Age predisposition

  • Any age of animal can be affected, but disease will be most significant in sexually mature individuals.

Public health considerations

Brucella abortus is a zoonosis risk and in the UK suspected human cases must be reported to the CCDC (Consultant in Communicable Disease Control). Other countries have equivalent reporting pathways.
  • Infection occurs through contact with cattle that have aborted (infected birth fluids, placenta, aborted fetus), unpasteurized milk or exposure within testing laboratories. Farmers, veterinarians and lab workers are most at risk.
  • Infection occurs through cuts in the skin or via mucous membranes.

Signs of human infection

  • Recurrent undulant fever in humans (recognized in 1850s).
  • Headache, weakness, sweating, chills, weight loss, aching.
  • Liver and spleen may be involved.
  • Often have periods of depression.
  • Can be chronic in nature as the bacterium can be intracellular and evade the immune system.
  • In endemic areas, brucellosis in humans may be confused with malaria or typhoid fever.

Cost considerations

  • Losses vary between regions and are dependent on the brucellosis rules in different countries.
  • In general, losses to cattle producers may include (but are not limited to) loss of the calf, decrease in milk yield, cost of treating retained placenta/metritis, subsequent reduction in the dam’s fertility, loss of individual or entire herds as a result of cull policies, loss of draught power, veterinary costs, lost access to international markets and in some regions vaccine costs.
  • The associated socioeconomic costs in relation to human health, in endemic areas, are extremely significant.

Special risks

  • Zoonosis risk.
  • Veterinarians investigating suspected brucellosis cases should take all necessary precautions to ensure they minimize the risk of infection to themselves and others in contact with the animal(s).

Pathogenesis

Etiology

  • Bacteria from genus Brucella; mainly Brucella abortus Brucella abortus in cattle. Brucella melitensis can be the causal agent in some regions of the world.
  • Main source of infection is from bacteria present in high levels in the aborted fetus, birth fluids and placenta.
  • Bacteria is also shed in milk and semen.
  • B. abortus can survive in the environment for several months, especially if it is cool and moist and will still be infectious.
  • There are wildlife reservoirs of bacteria, ie hare, bison, elk, feral pigs. This is a risk to cows but can complicate eradication efforts.

Predisposing factors

General

  • The primary source of Infection is the spread of infection from one animal to another, particularly at parturition.
  • In a naïve herd, this spread of infection may cause many animals to become infected and abortion storms to occur Abortion & stillbirths overview.

Pathophysiology

  • Infection occurs naturally by ingestion.
  • Initially, B. abortus is found in the regional lymph nodes and then invades the blood stream causing a bacteremia.
  • The bacteria then spread to colonize the supramammary lymph nodes, the mammary gland, the gravid uterus and placenta.
  • This causes the effects associated with the disease: placenta disruption, fetal death and contamination of milk.

Timecourse

  • The fetus is often retained for up to 3 days before being expelled.
  • Numerous bacteria are expelled from the genital tract at parturition and can continue to do so for up to 3 weeks following abortion.
  • Some cows which have previously aborted due to infection, will continue to shed brucella from their reproductive tract at subsequent, normal parturitions.
  • The organism is shed for a variable length of time in milk and may occur intermittently for the rest of that animal’s life.

Epidemiology

  • The main source of Infection is the spread of infection from animal to another, particularly at parturition. In a naïve herd, this spread of infection may cause many animals to become infected and abortion storms to occur
  • The disease is notifiable in the UK - all abortions must be reported to the APHA. In this way, an animal (and hence a herd) that is positive for B. abortus is identified. Measures are then taken to ensure spread does not occur to another premises.

Diagnosis

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Treatment

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Prevention

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Outcomes

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Further Reading

Publications

Refereed papers

  • Recent references from PubMed and VetMedResource.
  • Franc K A, Krecek R C, Hasler B N & Arenas-Gamboa A M (2018) Brucellosis remains a neglected disease in the developing world: a call for interdisciplinary action. BMC Pub Health 18 (125) BMCPubHealth.
  • Lalsiamthara J & Lee J H (2017) Development and trial of vaccines against Brucella. J Vet Sci 18 (S1), 281-290 PubMed.
  • Dorneles E S, Sriranganthan N & Lage A P (2015) Recent advances in Brucella abortus vaccines. Vet Res 46, (76) VetRes.
  • Millar M & Stack J (2012) Brucellosis - what every practitioner should know. In Pract 34 (9), 532-539 BMJ.

Other sources of information

  • Martin A (2009) Bovine Abortion Prevention. Vet Times. Website: www.vettimes.co.uk.
  • Smith B P (1990) Large Animal Internal Medicine. 2nd edn. pp 1405-1406.
  • Animal & Plant Health Agency (online) Official Veterinary Instructions – Brucellosis. Website: http://apha.defra.gov.uk.
  • APHIS (online) Facts About Brucellosis. Website: www.aphis.usda.gov (pdf download).
  • Centers of Disease Control and Prevention (online) Brucellosis. Website: www.cdc.gov/brucellosis.
  • Department of Agriculture, Environment and Rural Affairs (online) Brucellosis. Website: https://www.daera-ni.gov.uk.
  • Millar M & Aggett D (online) Brucellosis outbreak in cattle in Kenya and surveillance in Britain. Vet Times.

Organisation(s)