C613 - MELIOIDOSIS

IDevice Icon

C613 - MELIOIDOSIS 

Nature of the disease
Melioidosis is a bacterial disease caused by Pseudomonas pseudomalleiIt is primarily a disease of rodents that can spread to many species of animals, including humans. Heavy mortalities have been reported in sheep.
Classification
FAO List C disease
Susceptible species
Many species of animals are susceptible including birds, goats, sheep, pigs, horses, rodents and humans. There are also reports of infections in dolphins, tropical fish and non-human primates. It is potentially fatal in humans.
Distribution
Melioidosis occurs mainly in tropical countries. It is present in South East Asia and occurs in Australia (north Queensland), Papua New Guinea and in New Caledonia.
Clinical signs 
The disease may be acute or chronic, and clinical signs vary according to the location of lesions. Cases tend to be sporadic.
Sheep 
  • Weakness and anorexia leading to death within one week

In experimentally infected animals:

  • Pneumonia with respiratory distress
  • Severe coughing and profuse yellow muco-purulent discharge from the nose and the eyes
  • Other cases are lame with swollen joints, or partly paralysed
  • Some sheep show only fever and general weakness
  • There may be central nervous system involvement — circling, incoordination, nystagmus, spasms.

Disease may last several days or weeks.

Goats 

  • Disease is more likely to be chronic or sub-clinical
  • Abscesses may be palpable in superficial lymph nodes and udder
  • Lung involvement less severe than sheep and coughing is not a prominent sign

Cattle 

  • Rarely affected
  • May show pneumonia or central nervous system signs

Pigs 

  • Usually chronic and symptomless
  • Lymphadenitis, particularly of the submandibular nodes may be palpable
  • Can get acute septicaemia with fever, anorexia, coughing, nasal and ocular discharges
  • Rarely, there is reproductive involvement — abortions, stillbirths, orchitis in boars

Horses

  • Metastatic pneumonia
  • Fever
  • Colic and diarrhea
  • Lymphangitis on the legs
  • Affected horses may survive months with emaciation and oedema
  • Rare cases of nervous disorders have been described
Post-mortem findings 
The major finding is multiple abscesses that can occur in most organs, particularly the subcutaneous tissues, regional lymph nodes, lung, spleen and liver. 

The pus is thick or caseous, and green-tinged similarly to infections with Corynebacterium pseudotubercuilosis.

Differential diagnosis 
Other conditions producing multiple abscesses in various organs include:
  • Tuberculosis
  • Caseous lymphadenitis
  • Actinobacillosis

In horses meliodosis could be confused with:

  • Strangles
  • Glanders
Specimens required for diagnosis 
Swabs of nasal discharges and abscesses should be submitted for culture, blood samples can be submitted for serology ( ELISA, immunofluorescence tests).
Transmission   
In subtropical regions the main sources of infection are contaminated soil, mud and water. Insect bites and cutaneous abrasions, ingestion and inhalation can also be a source of infection.

Rodents appear to be the main reservoir of the organism. 
Goats’ milk has been found to be infected and drinking raw goats’ milk is a potential hazard. 

Direct animal to human or human to human transmission is rare.

Risk of introduction   
Contaminated soil and water could introduce the disease. Infected animals pass the organism in their faeces. As the disease in rodents has a long course, these are important reservoirs of infection and another potential method of introducing the disease.
Control / vaccines  
Attempts to treat cases with antibiotics have been disappointing. Because of the risk to humans, it is preferable to slaughter affected animals and destroy the carcass. The premises should also be disinfected.
References
  • Meliodosis, In Merck Veterinary Manual, National Publishing Inc. Eight ed, 1998, Philadelphia, p 481-482
  • Meliodosis, In Veterinary Medicine, Saunders, Eight ed, 1997, London p. 881-882
  • Office International des Epizooties, 2002