SHILOH, Ohio — Visitors from around the world to two upcoming events in Ohio’s Amish country could come away with more than they bargained for, health officials fear — a case of measles from the nation’s largest outbreak in two decades.

The outbreak, with more than 360 cases, started after Amish travelers to the Philippines contracted measles this year and returned home to rural Knox County, where it spread thanks to a lower rate of vaccination among the Amish and the difficulty public health authorities had in getting the word out to largely rural communities where phones are few and the Internet is nonexistent.

Health officials believe the outbreak is slowing in Ohio thanks to vaccination clinics and door-to-door visits by public health nurses. But Horse Progress Days, an international showcase of horse-drawn equipment scheduled for Friday and Saturday, is expected to draw more than 20,000 Amish and others from around the globe. And a large annual auction that raises money to help Amish families pay medical bills for children with birth defects is scheduled for Saturday.

Authorities are trying to spread education — and vaccination.

“Very easily someone could come for these events, be exposed to someone who didn’t know that they were sick, and travel home, and start another outbreak in another community somewhere in the United States or overseas,” said Dr. D.J. McFadden, health commissioner in Holmes County, site of Horse Progress Days and home to one of the country’s largest Amish populations.

The county has 54 cases of measles and one hospitalization. Most of its Amish were already vaccinated before the outbreak, McFadden said.

Symptoms of measles, which is caused by a virus, include fevers, coughs, rashes and pinkeye. Before widespread vaccinations in the U.S. beginning in the 1950s, 450 to 500 people died each year, 48,000 were hospitalized and nearly a thousand people suffered brain damage or deafness. Though nearly eradicated in the United States, measles remains common in many parts of Asia, the Pacific and Africa.

The Amish eschew many conveniences of modern life. Their religion does not prevent them from seeking vaccinations, but because their children don’t attend traditional public schools, vaccinations are not required and therefore not routine.

For Amish who aren’t vaccinated, Ohio health officials say, reasons include religious objections, unwillingness to shoulder the cost because they don’t have insurance, and not seeing the need for a disease that isn’t common.

Outreach efforts to deliver vaccinations and education have been hampered by communication — few Amish have phones — transportation and the strapped resources of rural counties without big health departments, said Richland County public health nurse Sue McFarren.

But when they’re contacted, most Amish have cooperated, she said. Officials have distributed about 10,500 vaccines in Ohio, about half in Holmes County in central Ohio. The other affected areas are mostly, but not all, nearby — in Crawford, Ashland, Coshocton, Highland, Holmes, Richland, Stark and Wayne counties.

“They have been excellent about quarantining themselves,” McFarren said. “If they have a case, they stay home until it’s run its course.”

Amish dairy farmer Daniel Weaver got a vaccination during a clinic at a pole barn near Shiloh in northern Ohio on July 25, concerned because he travels often.

“The Amish in general are not reacting that much differently than the rest of the population,” said Weaver, 48, of nearby Shreve. “It’s just because of our tight proximity, it creates a different effect.”

Several Mennonite families visited the same clinic, arriving one after the other in horse-drawn buggies with fluorescent orange triangles affixed to the rear. These “horse-and-buggy” Mennonites live a lifestyle similar to some Amish, though many have phones and other modern conveniences.

Mennonite dairy farmer Samuel Zimmerman, who got his vaccine after hearing about the outbreak, said he’d never really had an opinion about vaccines before.

“I guess when I was growing up we were hale and hardy, and we didn’t think about vaccinations,” said Zimmerman, 36, of Blooming Grove.

Organizers of Horse Progress days said they are distributing letters to international visitors warning them of potential measles exposure. Past events have drawn non-Amish from countries including Australia, Colombia, Germany, Mexico, South Africa, Sweden and New Zealand.

Posters will provide information about measles and encourage people with symptoms to go home, and a hospital will provide free vaccinations Friday, general coordinator Daniel Wengerd said.

Saturday’s auction for the Ohio Crippled Children’s Fund is being held at the Kidron Auction House in Wayne County. An auctioneer there said he wasn’t familiar with officials’ concerns.

The Ohio outbreak is the biggest in the U.S. since 1994. Overall, the Centers for Disease Control and Prevention are tracking 529 cases in 20 states, with the next biggest outbreaks in California and New York, none of which involve the Amish.