Etiologic agent = Coxiella burnetii

The name Q fever comes from the word "query," reflecting the unknown etiology of the disease when it was first recognized in Queensland, Australia in 1935. In the U.S., human Q fever has been reported most frequently from California.Coxiella burnetii is a rickettsial organism that is maintained in bird and rodent reservoirs in nature.

• Transmission among these natural reservoir species occurs primarily via ticks. Over 40 species have been implicated, and transmission may occur even via just inhalation of tick excreta deposited on animal wool.
• Transmission from wild animals to domestic animals is poorly understood.
  • Domestic animals may contract it via ticks, but likely spread it between themselves thereafter via aerosols.

The role of farm animals in transmission to humans:

Sheep are the most common source of infection for humans. The organism replicates to very high levels in the placenta (up to 10e9 infectious doses per gram of tissue) and is then shed in the reproductive tract fluids, exposing people attending the parturition. Infected animals also shed the organism in urine, feces and milk. Infection has also been associated with contact with sheep in abattoirs, and, less frequently, with cattle and goats.

• Coxiella burnetii can be extremely infectious for humans - just a single organism is sufficient to initiate infection with certain strains of the organism- but in other cases infections may be subclinical.
• Infection in the farm animals themselves is also often subclinical, but C. burnetii infection may be a cause of abortion, because of placentitis, in sheep, cattle and goats.
  • Control procedures to reduce spread of C. burnetii during an outbreak in sheep and goats may include:
    • Lamb/kid inside a building.
    • Keep ewes/nannies and lambs/kids indoors for 14 days after parturition.
    • Collect placentas and stillborn fetuses in sealed containers for disposal.
    • Compost contaminated straw and feces under wind- and weather-proof plastic for 2 years.
    • Shear only inside a building.

Examples of recent outbreaks of Q-fever:

• 1996: 10 people who adopted goats from a humane society in San Mateo County, CA contracted Q fever.
• 1996: 25% of the residents in a small town in Germany were infected in association with lambing time.
• 1997: 26 abattoir workers were infected in one town in Australia. (Other workers were subsequently vaccinated.) Another outbreak occurred among 24 abattoir workers in 1998.
• 1998: widespread outbreak in Japan
• 1999: large-scale outbreak of abortions in goats and infections in 37% of the 179 farm personnel working with those goats in Newfoundland
• 2001: A similar outbreak occurred among goats and goat farm personnel in Wyoming.
• 2000-2001: long-term outbreak among sheep in Germany
• 2001: 3 workers involved in the foot and mouth disease culling procedures in the UK contracted Q fever.
• 2002: 15 UN staff in Bosnia who worked in an office near a sheep farm were infected.
• 2002: Dozens of residents and tourists in the Chamonix Valley in France were infected, presumably via airborne contamination from infected animal herds in the valley.

The role of dogs and cats in transmission to humans:

Some of the most interesting recent cases (see references) of Q fever have involved contact with parturient cats (people playing poker in the room where a cat was giving birth!) and dogs (there are at least 2 family outbreaks associated with dogs). In each case, a subgroup of the litter died shortly after birth.

• Estimates of seropositivity rates for dogs and cats range from 1-66% (most commonly 15-20%), depending on the population surveyed.

Q fever's clinical presentation in people:

People are most often infected by inhalation of the organism from reproductive fluids. However, you can also be infected via the oral route following direct contact with the organism or by consuming contaminated, unpasteurized milk. Transmission via raw milk was historically a very important route of infection. In fact, pasteurization of milk was instituted in part to prevent transmission of C. burnetii.

• Q fever presents as an acute febrile disease with malaise, myalgia, headache, chills and sweats. It can also lead to pneumonitis (with coughing) and chronic endocarditis, pericarditis, hepatitis, meningoencephalitis, optic neuritis, or osteomyelitis.
  • Mortality is <1% if appropriately treated with tetracyclines.
• Reports of human-to-human transmission are extremely rare, but C. burnetii has been isolated from human milk and human placental tissues, and there are reports of transmission to physicians during abortion procedures and autopsies.

An experimental vaccine is available from the U.S. Armed Forces for those working experimentally with the organism in a laboratory setting or with pregnant sheep. It is not currently available nor recommended for veterinarians who work with sheep in routine practice settings.

References:

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