B057 - Q FEVER

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B057 - Q FEVER 

Nature of the disease
Q fever is an important zoonosis caused by infection with the rickettsia Coxiella burnetti. This organism can infect a wide range of wild and domestic animals. Infection in animals can cause abortion or be asymptomatic.
Classification
OIE List B disease, level 3 of biosafety 
Susceptible species
Infection is common in cattle, sheep, goats and dogs. Cats, horses, donkeys and pigs. Infection of pigeon, geese and fowl have also been described. There are a number of wild animal reservoirs, with marsupials such as the bandicoot being considered important in Australia.

The principal reservoirs of human infection are cattle, sheep and goats.

Distribution
The organism is found world-wide and serological evidences are found in Australia, however, incidence of the disease is low except in certain occupational groups that work with animals or in slaughter plants.
Clinical signs 
In cattle, sheep and goats infection is usually sub-clinical or just associated with fever and mild bronchopneumonia. Occasionally Q Fever causes abortion, retained placentitis, endometritis and infertility.

In humans, Q fever might be asymptomatic but can also be responsible for infleunza-like syndrome including:

  • Severe headache
  • Chills and fever
  • Endocarditis
  • Hepatitis
  • Osteomyelitis with aches and pain in various muscles and joints
  • In about 50% of cases there is pneumonia. 

In untreated cases the fatality rate is less than 1% and most patients recover after an illness lasting 1 to 3 weeks. Up to 20 to 30% of acute cases go on to develop a chronic post Q fever debility syndrome.

Post-mortem findings 
In rare cases where human mortalities occur, pneumonitis or endocarditis may be seen.
Differential diagnosis 

In animals the differential diagnosis include other causes of abortion and infertility:

  • Leptospirosis
  • Brucellosis
  • IBR
  • BVD
  • Campylobacteriosis
  • Listeriosis
  • Salmonellosis
  • Chlamydiosis
  • Mycotic abortion
  • Severe deficiency in vitamins A, E or Selenium
Specimens required for diagnosis 
For identification of the bacteria, samples from placenta, vaginal discharges, stomach contents of aborted foetus and milk or colostrum can be attempted, but this is considered hazardous to laboratory workers (only performed in biosafety level 3 laboratories). Techniques include microscopic observation, inoculation and DNA probe.

Serological tests are preferentially used, they include Indirect Immunofluorescence Test,  ELISA and Complement Fixation Test.  

Transmission   
Transmission occurs through many possible ways:
  • Inhalation of aerosols dust containing the organism, is very important in human transmission,
  • Arthropod vectors, especially ticks, which are the primary source of transmission in wild animals,
  • Direct contact of any contaminated material, 
  • Sexual transmission,
  • Ingestion of placenta or other reproductive discharges,
  • Ingestion of raw milk, urine or faeces,
  • Contact of infected ticks' faeces

The organism can survive in the environment for 7 to 10 months. The faeces of ticks can contain C. burnetti, which can remain infectious for extremely long periods.

People become infected mainly through close contact with infected animals, especially from handling body fluids and viscera. Placental tissues and fluids are recognised as a major source of infection. Thus, people working in abattoirs, stockyards, livestock transport industry, rendering and hide processing plants, as well as farmers, shearers, veterinarians and laboratory workers are at risk.

Risk of introduction   
Q fever is most likely to be introduced with imports of infected ruminants. Pregnant animals represent the highest risk.

Introduction of infective ticks present on any susceptible species should also be considered as a potential threat.

Control / vaccines  
Because the disease does not cause substantial problems or production loss in animals, there is little imperative to treat or prevent the infection in animals. However if an outbreak occurs with significant infertility and abortion, antibiotics (tetracycline, chloramphenicol) are effective and inactivated vaccines are available but not licensed in every country (e.g. banned in USA).

Control measures that can decrease the prevalence of infection include:

  • Pasteurisation or sterilisation of milk;
  • Removal and destruction of placentae;
  • Removal and destruction of bedding, straw and other contaminated materials; and
  • Disinfection of vehicles used for animal transport.

In humans, treatment involves early recognition and prompt treatment with tetracycline or doxycycline. Acute cases respond well, but chronic cases are less responsive. Following recovery, immunity is generally for life.

In Australia, a human commercial vaccine was released for general marketing in 1989. The vaccine is safe, highly effective and provides long lasting immunity. Because vaccination of persons previously exposed to Q fever, either through natural exposure or previous vaccination can result in severe local reactions, screening for prior immunity, by serological and intra-dermal testing, is essential.

References
  • MARRIE TJ (1998) Q FEVER In Zoonoses, ed by SR PALMER, Lord SOULSEY and D.I.H. SIMPSON, Oxford University Press, Bath Press, Avon, 1998, p.171-185
  • Office International des Epizooties, 2002
  • Q Fever, In Merck Veterinary Manual, National Publishing Inc. Eight ed, 1998, Philadelphia, p 486-487
  • 'Q' Fever, In Veterinary Medicine, Saunders, Eight ed, 1997, London p. 1158-1159