A dog-killing worm is on the loose in California

An invasive parasite that can kill dogs is now lurking in Southern California.In new research this week, scientists say they have confirmed new spread of flatworms Heteropenia americana to the area. Researchers say the parasite is not considered a threat to humans, but it could pose a new threat to pets and animals living along the long Colorado River.

Han Americans is one of many species of worms nicknamed liver flukes. Their immediate hosts are snails, which carry and release the parasite’s larvae (the free-living form) into freshwater. Once these larvae encounter their next compatible victim (also called a definitive host) in the water, they pass through the skin and migrate first to the lungs, liver, and then certain blood vessels along the lining of the intestines. From there, they mature into adults, mate and lay eggs, which are expelled and used to infect the snail, restarting the life cycle. Raccoons are the primary definitive host for this species, but the worm can also infect and lay eggs in other mammals, including dogs and horses.

Study authors' description of the worm's complex life cycle.

Study authors’ description of the worm’s complex life cycle.
illustration: Bania et al/Pathogens.

When these worms infect dogs, they cause a condition called canine schistosomiasis. Much of the damage caused by this infection comes not from the worms that first invade the body, but from the next generation of eggs they lay, which circulate through the bloodstream and may eventually make their way into the intestines and other organs. They then damage the body by causing inflammation and forming clusters of immune cells called granulomas. Symptoms tend to be gradual at first, such as lethargy and weight loss, but if left untreated, the infection can lead to life-threatening organ failure.

It was previously thought that only one species of snail could naturally serve as a direct host for these worms, galba cuba, but scientists recently discovered that at least two and possibly three other snail species can carry it. Likewise, while parts of Texas and other Gulf Coast states have historically seen cases of infection in dogs, veterinarians and pet owners are now beginning to report cases elsewhere, including in California. From 2018 to 2023, a total of 11 cases occurred report All the dogs in the state are from Southern California and are related to dogs that visited the Colorado River, which Supplies It accounts for one-third of the region’s water volume.

flatworms like Han Americans Typically, this isn’t the strong suit of study author Adler Dillman, a professor of nematology (the study of roundworms) at the University of California, Riverside. But when colleagues approach him for help, he doesn’t pass up the chance to investigate the cases of these mysterious arrivals.

Dillman and his team decided to find Han Americans in its supposed new hunting grounds. They traveled to river areas where dog cases may have occurred, collected snail samples, and brought them back to the lab, hoping to catch some of the worms just as the snails were about to fall off.

“It was a bit like finding a needle in a haystack because we were trying to pick up a snail that was infected about three weeks ago… when we saw [the worms], we all jumped up and down excitedly to take pictures. It’s an exciting time for us,” Dillman told Gizmodo. “But it’s bad news for people who live in and around the area because now there’s this parasite to worry about. “

The researchers also sequenced the DNA of snails and worms and found the apparent presence of Han Americans Inside not one but two snails, Medan, Cuba and Garba Low—an unexpected discovery for a number of reasons.

“First, these snails have never been reported from the Colorado River before, and certainly not this far south. We found these two species present in the same place at the same time, which is unusual and has not been reported before,” Dee said. Mann said.

There are other types of worms that can cause severe schistosomiasis in humans, but exposed to Han Americans Seems to cause a mild rash at best. And the infection cannot be passed from dog to dog or from dog to human, but only through direct contact with the worms in contaminated fresh water.

But these worms do pose a greater risk to dogs and other animals than previously thought. There have been recent reports of infections in other non-endemic areas of the country near the Colorado River, so it is likely that the river is spreading the snails and worms widely.

“This is probably a bigger problem — not just in Southern California, but in parts of Nevada, Utah, Colorado” and New Mexico that are connected to rivers, Dillman said.

Another unanswered question is how the snails got into the river in the first place. “Climate change may be a factor, but human activity is certainly a factor as well. We just don’t know,” Dillman said.

Now, the scientists hope their work will help protect dogs and their owners from the parasite.

“It’s good to know that’s a possibility. So you might want to go somewhere different, you might not want to be in this part of the Colorado River. Or maybe you can keep a close eye on your dog and know what the possible causes of any illnesses are. ,” Dillman said.

Although Dillman mainly studies roundworms, he wants to continue his research Han Americans If he could. He noted that roundworms and the infections they cause are often used to learn more about how the immune system works, but these and similar flatworms may also have unique lessons to teach us.

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