SAO PAULO — A measles outbreak is growing in Brazil after cases were imported from neighboring Venezuela where health services have collapsed.

More than 460 cases of the disease have been confirmed in two Brazilian border states, the Health Ministry said Monday. There are also concerns that the outbreak has reached an isolated tribe that lives in the Amazon that has little resistance to such diseases.

The cases in Brazil come after the World Health Organization declared the Americas measles-free in 2016. But outbreaks can still occur even after a country is declared free because cases can be imported. That's just what has happened in Brazil, where the disease slipped across the border with people fleeing economic and political collapse in neighboring Venezuela.

Measles spreads through the air and is highly contagious. While there is no specific treatment for the disease, the vaccine is very effective. Symptoms of measles include fever, runny nose, cough, sore throat and a rash that spreads over the body.

Last year, measles started spreading in Venezuela, where there have been more than 2,000 cases.

Oil-rich Venezuela was once wealthy, and the health system there was a model for the region. But mismanagement and a fall in oil prices have led to widespread shortages of everything from food to medicine. Doctors have fled and health services have collapsed.

Hardships in general in Venezuela have sent more than 1 million people fleeing to neighboring countries, sometimes bringing disease with them.

To combat the outbreak, authorities in Brazil are offering measles vaccinations to foreigners registering with the federal police and are also increasing efforts to ensure Brazilians are vaccinated. Brazilians should be vaccinated against measles as a matter of routine, but authorities have recently held special campaigns in Roraima and Amazonas to vaccinate those who slipped through the system.

Beyond the usual concerns of containing the extremely contagious disease, Survival International said an outbreak could devastate the isolated Yanomami tribe, which lives on both sides of the Brazil-Venezuela border, deep in the Amazon. So far, 23 Yanomami with measles symptoms have sought medical treatment in Brazil, the indigenous rights organization said, and one of those cases has been confirmed. Many more could be sick in Venezuela, where Survival International said it is harder to get information.