Wednesday, May 28, is National Hamburger Day, an unofficial holiday that celebrates America’s favorite sandwich.

The origins of National Hamburger Day are unclear. The National Day Calendar says the origin of the hamburger itself is surrounded in controversy, but that it most likely first appeared in the 19th or early 20th centuries and has grown in popularity over the years.

There are many spots in Pennsylvania cooking up delicious burgers.

This Philadelphia Brewery might not specialize in the burger, but its standalone “Hygge Burger,” with both ground chuck ad brisket beef, sharp cheddar, bibb lettuce, red onion, garlic-dill pickles and special “Hygge Sauce” on a brioche bun. Take it to the next level by adding bacon or a fried egg, or go vegetarian with a patty made with mushroom and barley, topped with homemade bread-and-butter pickles and cabbage slaw.

Bar Hygge, pronounced “hyoo-guh,” is located at 1720 Fairmount Ave. Hygge is a Danish word that means “a quality of coziness and comfortable conviviality that engenders a feeling of contentment or well-being.” It touts 4.6 stars out of 601 reviews on Google.

Back to National Hamburger Day…here’s a list of some freebies and specials being offered by restaurants in the Keystone State:

Buffalo Wild Wings: On Wednesday, the participating locations are offering any burger at half price, including the All-American Cheeseburger and the Triple Bacon Cheeseburger (offer good for takeout or delivery using the promo code GOBURGER on the app; not valid for dine-in orders).

Burger King: Free hamburger with a $1 purchase for rewards club members on Wednesday.

Checkers & Rally’s Drive-In: Through Friday, the Cheese Double combo costs $3.

Dairy Queen: Through Sunday, rewards club members who buy Signature Stackburger get a second one free. The deal is available on the DQ mobile app.

Friendly’s: Through Saturday, join the fast-food chain’s rewards program on the app get a free Founder’s Burger.

Perkins: The chain’s National Hamburger Month special continues through Saturday. The Great American Burger Trio — a cheeseburger, fries and pie— costs $9.99.

Shake Shack: Through Sunday, get a free ShackBurger with a $10 or more purchase (order in the Shack app, online or in-Shack kiosks; use code BURGERMONTH).

Smashburger: On Wednesday, any single burger costs $5.28 (offer good at participating locations nationwide; redeem the deal in-store or through Smashburger’s website and app with the code JUST528).

Wendy’s: From Wednesday through Sunday, customers using the Wendy’s app can get a Jr. Bacon Cheeseburger for a penny with any other purchase.

White Castle: Throughout May, the chain is celebrating National Hamburger Month with special offers, including a “Slider-bration” event where sliders sell for 25 cents, along with other promotions.

Sources for this report are USA Today, Finance Buzz and restaurant websites.

A big part of the reason they’ve managed to spread so quickly, Price said, is that they’re parthenogenetic, which means females are capable of reproducing asexually without the aid of male ticks.

“So the implications of this mean that a single individual female that lays around 2,000 to 2,500 eggs, all without mating, can create an entire population just by that individual,” Price said. “There’s no other tick in North America that reproduces in this manner. And it’s this unique reproductive strategy that enables the Longhorn tick to very successfully and very rapidly invade new geographic regions across the state and the country.”

He added that migratory hosts, including white-tailed deer and black-capped night herons, are capable of carrying the ticks across vast distances, which also accounts for their rapid geographical spread.

Potential threats to public health

One of the biggest questions researchers are asking about longhorned ticks is how much of a threat they pose to humans.

Past research out of Asia has found that longhorn ticks can carry a large variety of pathogens that affect human health.

“But it’s not 100% clear if it actually vectors those pathogens,” Phillips said. “So even if it has the bacteria or the virus inside of it, is it going to give it to you if it bites you? That’s not 100% clear. So that’s part of what we were trying to figure out in our research.”

To investigate that question, Phillips, along with Temple University ecologist Jocelyn Behm and undergraduate student Jackson Fahey, collected longhorned ticks from forested areas around the Philadelphia area, and tested them for pathogens. The results were good.

“None of the ones that we collected carried any pathogens,” Phillips said. “So if you get bit by one around Philadelphia, you hopefully aren’t going to get a disease right away.”

Those findings match with other, previous rounds of testing that likewise found that longhorned ticks aren’t yet carrying some of the pathogens most dangerous to humans.

But that’s not the end of the story. Price said that some of his lab’s current research has discovered multiple pathogens of human health concern in longhorned ticks collected from Pennsylvania parks and public use areas. Among the pathogens they found is the bacteria responsible for causing Lyme disease, though Price added that studies from Centers for Disease Control and Prevention have shown that longhorned ticks are less likely to spread Lyme disease because the bacterium tends to be lost during their molting stage.

Still, Price said, the tick is so new that the role it plays in terms of disease transition remains largely uncertain.

However, past studies have found that longhorned ticks are capable of spreading several pathogens that can be found in Pennsylvania, including Rocky Mountain Spotted Fever and Powassan virus, a rare but serious disease that can cause encephalitis and meningitis.

“Typically with Borrelia burgdorferi, the bacterial agent responsible for Lyme disease, the tick has to be attached for 36 hours before that bacteria can be transferred through the bite to an individual,” Price said. “But with Powassan virus, it’s only about 15 minutes, and that’s just because the virus is maintained in the mouth parts and the salivary glands compared to the Lyme disease bacteria that’s maintained in the midgut of the tick.”

Price added that Phillips’ study helped demonstrate that there is significant overlap in habitat between longhorned ticks and local ticks, which provides a potential pathway for pathogens to be transmitted between the species.

Also of concern is the fact that longhorned ticks are more aggressive in their pursuit of hosts and more likely to swarm than other ticks, as well as findings indicating that they’re more likely to be found in areas where local ticks typically don’t reside, like manicured lawns. They’ve also been found to affect domestic animals, like dogs, and can pose significant threats to livestock like cattle.

Luckily, longhorned ticks can be protected against using the same methods recommended for local ticks, including keeping your skin covered, and the use of repellents approved by the U.S. Environmental Protection Agency, like permethrin.