The US military is ordered to place the contagion of swine flu under close observation with the disease having reportedly afflicted 40 people in the country.

“The US military is monitoring the situation closely,” Pentagon spokesman Bryan Whitman was quoted by AFP as saying on Monday.

The Defense Department was “monitoring the health of the force to make sure we’re taking the necessary precautions to be able to preserve the fighting force,” he added.

The World Health Organization has so far confirmed 73 cases of the viral disease worldwide.

Later in the day, a recent Spanish visitor to Mexico was declared the most recent to have contracted the flu. Three suspected sufferers have also been reported in Germany, further alerting the European health authorities.

US Secretary of State Hillary Clinton, meanwhile, warned that the State Department might prevent ‘non-essential’ trips to Mexico where the first case of the disease was detected, FOXNews reported.

The WHO, however, has not advised any travel bans and President Barack Obama has been seen maintaining his air of calm when addressing the matter.

“This is obviously a cause for concern and requires a heightened state of alert…. But it’s not a cause for alarm.”

California, Texas, and New York City have reported swine flue cases. The country has been using Tamiflu and Relenza antivirals, deemed to be effective against the virus, named H1N1.

The newly-spread disease turns out to be an unknown strain for which no vaccine has been developed.