Scientists at Neiker-Tecnalia, the Basque Institute for Agricultural Research and Development, have evaluated the effect of treatment with antibiotics and vaccination in controlling Q fever in sheep flocks. This disease mainly causes abortions, although it can also lead to premature births, low weight and weakness in newborn lambs. The control of this disease is of great importance in animal production, as it spreads easily among the animals and causes significant economic losses, and mainly because it can be transmitted to people in contact with infected livestock.
Q fever is a zoonotic disease -one that animals can transmit to humans- spread all over the world and caused by the bacteria Coxiella burnetii. In animals it causes mainly reproductive problems. In people, Q fever can be asymptomatic or like a flu syndrome; however, in acute cases pneumonia and/or hepatitis can appear.
Neiker-Tecnalia's research has been focussed on sheep, since this species is one of the main reservoirs of infection in the Basque Country. The researchers found that 74% of the flocks of sheep in the Basque Autonomous Community (region) had at least one animal with Coxiella burnetii antibodies. Presence of antibodies indicates that the animal has been in contact with the bacteria, but it does not mean that it has necessarily developed Q fever. In the case of goats herds the percentage of seroprevalence was 45%; and in cattle herds, 43%.
The first method used to control Q fever in naturally infected flocks was based on the application of the antibiotic oxytetracycline. The researchers gave the antibiotic to pregnant ewes at 100 and 120 days of gestation, and abortion rate was reduced to levels lower than 4%. However, oxytetracycline did not prove to be effective in reducing the infection nor the number of bacterial shedding. So Neiker-Tecnalia is proposing that a greater research effort has to be done in this field of veterinary medicine, since there are few antibiotics authorized for sheep that are effective against intracellular bacteria like Coxiella burnetii.
Vaccination, a promising method of control
The use of an inactivated vaccine to control the disease offered more promising results. The vaccine Coxevac ® was used and its effectiveness was proven in the short (1 year) and long term (4 years). No immediate effects were noticed during the first year following vaccination, because the flocks studied had a high percentage of infected animals. However, with routine annual vaccinations it was possible to gradually reduce the infection until its disappearance after four years of vaccination.
The vaccine was beneficial in controlling abortions which, after the first year of vaccination, were significantly reduced (<2%). Q fever is responsible for abortion rates between approximately 6% and 10% of the ewes in an infected flock.
After four years of vaccination, the absence of the infection in the animals did not necessarily mean that the bacteria Coxiella burnetii had been eradicated on the sheep flock, since this bacterium is very persistant in the environment, and it remains present in sheep premises (surfaces, floor, aerosols) for long periods of time. So Neiker-Tecnalia recommends that after an outbreak of Q fever in a sheep flock, vaccination should be implemented for a period of five years at least. It is very important that replacement lambs are immunised against the bacterium when they reach three months of age.
Means of eliminating Coxiella burnetti
Neiker-Tecnalia scientists found that the main Coxiella burnetti shedding routes in sheep are vaginal fluids and faeces; and to a lesser extent, milk. Bacterial shedding through milk is basically concentrated in the first month after lambing, while vaginal and faecal excretion is more prolonged in time. Bacterial excretion favours the generation of contaminated aerosols and the presence of the bacteria in the air in livestock premises, so there is a risk of Q fever transmission to susceptible animals, and to people in contact with infected animals.