Brazilian officials said Wednesday they are investigating an outbreak of the highly contagious disease glanders among horses stabled close to the site of next year's Olympic riding contests.

There is alarm in the equestrian community over the appearance of the disease just when riding events start on Thursday to test the Olympic preparations at Rio de Janeiro's Deodoro complex.

The Agriculture Ministry says at least one horse diagnosed with glanders and subsequently killed to stop the disease from spreading had spent several months at the Army Equestrian Complex in Deodoro, which is just a few hundred meters from the Olympic site.

However, officials insisted there was no risk of the disease -- which can infect humans as well -- spreading to participants during this week's test events.

"The installations where the riding tests for next year's Olympic Games will take place... are under a complete quarantine and rigorous bio-security measures," the ministry said in a statement.

"There are and won't be any health problems during the riding test events."

All 584 horses in the army facility are being subjected to a series of tests with samples sent for analysis at a laboratory in Germany. The tests are to run into October.

Since some of the horses from the army facility have been used at another of the city's riding centers to the south, the approximately 300 horses kept there are also being tested and kept under strict quarantine.

In total, 17 horses diagnosed with glanders are being kept in Brazil's Sao Paulo state, awaiting further examination and extermination.

Glanders is a sometimes fatal, incurable disease which causes ulcers in the respiratory tract and spreads through cuts, sneezing or contaminated food and equipment.