Veterinary officers along Greece's northeastern borders had increased health checks after 20 people in southern Bulgaria were infected with brucellosis, officials said on October 1.

In the southern Bulgarian Town of Harmanli 20 people had been infected from contact with sick goats and sheep, Agence France-Presse (AFP) quoted a Bulgarian veterinary officer.

Cars crossing the Greek border were being sprayed with disinfectant and local farmers have been told to keep their flocks indoors for the duration of the alert, the animal health department of the Greek town of Komotini said.

Brucellosis is also called undulant fever or Malta fever and is an infectious disease transmitted from animals to humans, caused by bacteria.

The disease is transmitted either through contaminated or untreated milk and milk-products or through direct contact with infected animals.

Four other people had been infected from an outbreak in a flock of sheep and goats in September, AFP said.

Diagnosing the disease is difficult as initial symptoms resemble flu, including weakness, fever, sweating, headache and pain in the joints.

The disease could be fatal but it could not be transmitted by humans, AFP said.