Fears over a multi-state measles outbreak are growing after a person infected with the virus traveled from Illinois to Missouri.

An unvaccinated person has visited the St Louis Aquarium, a highly frequented destination that attracts over a thousand daily visitors, potentially spreading the infection to numerous individuals.

They also ate at a restaurant, although the name or type was not revealed, before returning to southern Illinois.

They were in the aquarium from 1 to 6pm last Wednesday, April 30, with officials warning visitors they could have been exposed.

This incident occurs during a significant outbreak in Texas, where more than 800 individuals have fallen ill and two young girls, aged six and eight, have tragically died. It is the largest outbreak to affect the US in the last 20 years.

Measles is the most contagious disease globally, with an infected person capable of transmitting it to nine out of ten unvaccinated people they come into contact with.

The outbreak is currently condensed in Texas, with Gaines County in the Panhandle region at the epicenter, but in recent weeks cases have spread to seven other states.

No measles cases in Missouri have been linked to the patient to date, although people are being urged to monitor for symptoms, including a large, red rash. 

The above map shows Missouri and Illinois and the locations where measles exposure alerts have been issued in the area in recent days

There is also no evidence at this point that any measles cases in Missouri or Illinois are linked to the outbreak in Texas.

Missouri has detected three measles cases so far, although none of these have been linked to the sick patient who visited from Illinois.

Two of the cases have been detected in New Madrid county, in the south of the state, while the third was detected in a child in Taney County, in the state’s southwest, who had recently returned from abroad.

In Illinois, a total of six measles cases have been detected to date, including four in Marion County — which includes the patient who traveled to Missouri’s aquarium.

Two other cases were detected last month in Cook County, Chicago, but these were linked to international travel.

The cases in southern Illinois have already prompted warnings for people who visited local grocery stores, a gym, restaurant and a launderette.

In Missouri, the patient who visited the aquarium has been unable to give officials a ‘concrete’ timeline of their movements. 

Dr Mati Hlatshwayo Davis, the director of health for St Louis, told a local broadcaster: ‘We are only as strong as the willingness for individuals to speak to us and to provide details.

‘We are trying to get more information from the individual.’ 

St Louis aquarium said that 939 people visited the attraction on the day the measles patient was there, including a school group.

Visitors are now being contacted to warn them that they may have been exposed to the virus and to ask them to report any symptoms.

A young boy infected with measles (stock image) 

The aquarium says that all its surfaces are cleaned multiple times throughout the day and that animals cannot get the disease.

Officials say the best way to prevent an infection with measles is to get vaccinated against measles.

The risk of being infected is slashed by about 93 percent after just one shot and 97 percent after two, estimates suggest.

Measles is a highly infectious disease spread by coughs or droplets in the air, and can infect nine out of ten unvaccinated people that are exposed to it.

The disease starts in a similar way to the flu, with coughs and a fever, but patients will quickly develop the characteristic rash, which starts on the head before spreading across the whole body.

The disease attacks the immune system and weakens it, raising the risk of other infections — like pneumonia — which can be fatal.

Doctors treat measles using antibiotics for secondary infections, as well as drugs to reduce fever and other symptoms.