Glanders

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Burkholderia mallei
Phylum Proteobacteria
Class Beta Proteobacteria
Order Burkholderiales
Family Burkholderiaceae
Genus Burkholderia
Species B.mallei

Also known as: Farcy Caused by Burkholderia mallei Also known as: Pseudomonas mallei — B.mallei

Introduction

Glanders is a contagious disease caused by Burkholderia (Pseudomonas) mallei. It exists in acute and chronic forms. Animals are infected by ingestion of contaminated feed or water, inhalation or via open wounds. The organism invades mucosa and disseminates to other tissue via the lymphatics resulting in nodules and ulcers in the respiratory tract and on the skin.

Burkholderia mallei is a species of the Burkholderia genus. The presence of B. mallei in the host causes hypersensitivity reactions.

Three forms of the condition have been described; animals will show signs of one or more forms.

Pulmonary form:

Small calcified or caseous nodules develop in the lungs, the surrounding tissue becomes inflamed and consolidated. The resulting pneumonia causes respiratory distress and coughing. The nodules frequently degenerate and release their contents into the bronchioles which results in spread of the infection into the upper airways.

Nasal form:

Nodules form on the nasal mucosa, nasal septum and nasal turbinates. These break down to become ulcerative with raised irregular borders, the lesions may heal to form characteristic star shaped scars. A thick mucopurulent discharge is seen at the nostrils. The local lymph nodes are enlarged and as the disease progresses, they become firm and adhere to underlyinig tissues.

Cutaneous form (Farcy):

Nodules form overlying lymph vessels, especially of the extremities and limbs. These nodules rupture to release thick pus which is highly infectious.

Carnivores can also be infected by ingestion of infected carcasses. The disease is zoonotic, humans are infected by inoculation through a wound and mortality is high.

Signalment

Equidae are most commonly affected, horses tend to get the chronic form and mules and donkeys the acute form. The disease was once widespread in the UK but was eradicated in 1928 and is now a Notifiable disease. Animals imported from areas at high risk of the disease must be blood tested before entry into the UK is permitted. Distribution is limited to parts of SE Asia, The Middle East, India, North Africa, China and Mongolia.

Diagnosis

A diagnosis of B.mallei can be made by collecting specimens, including discharges from lesions and blood for serology. The bacteria grows on media containing 1% glycerol. Most strains are non-lactose fermenters on MacConkey agar. Complement fixation and agglutination can be carried out, as can serology.

Clinical Signs

Clinical signs may be sufficient to diagnose the condition, however they do not develop until the disease is advanced, therefore specific tests are indicated in suspected cases to aid prompt diagnosis.

Acute

  • Pyrexia
  • Mucopurulent nasal discharge
  • Ulceration of nasal mucosa
  • Coughing
  • Death

Affected animals are septicaemic and die within a few days.

Chronic

  • Nodular, ulcerative nasal lesions
  • Subcutaneous nodules which rupture and discharge exudate
  • Enlarged lymph nodes

Animals are debilitated and show clinical signs for several months, the disease may be fatal or the animal may appear to recover but it will act as a carrier and source of infection for spread of the disease.

Clinical Tests

The Mallein test is used most frequently to diagnose the condition, a fraction of the causative organism is injected intradermally into the eyelid or applied as eyedrops, a positive result is seen as local swelling and discharge 1-2 days post testing.

Laboratory Tests

Other diagnostic tests include an Elisa, complement fixation and culture of the organism from exudative lesions.

Treatment

There is no vaccine available. Prevention and control focuses on prompt detection and slaughter of infected animals and complete quarantine and disinfection of the affected premises.

Prognosis

Prognosis is poor, the disease is usually fatal. Animals which survive should be slaughtered to prevent spread of the disease.

Also see: Glanders in Donkeys



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