Pennsylvania Articles: BACK
Hate ticks? Save deer
Ivan Oransky
The Scientist
Volume 21 | Issue 1 | Page 20
If you thought it made sense to decrease disease-carrying ticks in your area by removing the deer that harbor ticks, Sarah Perkins has some news for you. Perkins, a postdoc in the Center for Infectious Disease Dynamics at Pennsylvania State University, recently looked at studies in which researchers removed deer from large areas, called deer exclosures, using deer-proof fencing of various kinds. The studies tended to find fewer ticks at the nymph stage, which is when they can transmit tick-borne encephalitis (TBE) virus and other diseases. But when they removed deer from smaller areas, they found more nymphs.
To try to understand that apparent paradox, she looked at transmission of the virus. Adult ticks lay thousands of eggs on blades of grass. The larvae and nymphs are lower to the ground, and tend to find mice to feed on, while adults typically feed on deer. Larvae, which are naïve to TBE, co-feed (see image). A nymph tick will feed in one spot, and a cluster larva finds a spot nearby. Langerhans cells are attracted to the original bite site and then carry the virus to the site where the larval tick is feeding. "It's absolutely bizarre," says Perkins. This unusual method of transmission was first demonstrated in Thogoto virus, another arbovirus, by Linda Jones and colleagues ( Science , 237:775-7, 1987).
The paradox, then, made sense, because deer are "a dead end for the pathogen," says Perkins. In large exclosures, the absence of deer reduces the overall population of ticks effectively. However, there seemed to be an inflection point at about 2.5 hectares. "As the size of the deer exclosures got smaller, there was a flip," she says. Excluding deer from smaller areas perhaps meant that ticks were transferred from deer to rodents outside the exclosure and then imported into it.
Perkins wanted to test the hypothesis that small exclosures somehow fostered nymph growth. She was able to make use of .64-hectare exclosures that had been created 16 years ago by the forest service in the province of Trentino, Italy. The exclosures are 2 meters high, so they exclude deer but not rodents and other small animals.
The researchers at the facility - a converted Austro-Hungarian hospital 1,500 meters up a mountain - get three waiter-served meals a day, and of course fine Italian wine. The province supports the research, she says, because of interest in anything that can infect tourists. The ticks like to bite mushroom hunters, who ply the same fields as the researchers. "They always ask us if we've seen any porcinis," says Perkins.
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Lyme-infected ticks hit early this year
Kathy Stevens
The York Dispatch
York, PA
March 7, 2007
Jan Klinedinst was on it.
She'd scheduled Lyme disease vaccinations for both of her 8-month-old Labradors long before the tick season supposedly begins. Lionheart, the blond retriever, and Bear, the chocolate, were to receive vaccines while she was away on vacation.
But she returned to bad news: both already were infected.
"If we have an outbreak in March, I have a feeling it's going to be a bad summer," she said, and warns York County residents to beware both for their own health and that of their pets.
While she's no expert on Lyme disease, she knows that deer ticks usually decrease in numbers during the winter. She knows the deer tick season runs from mid-spring through late fall.
Still, Klinedinst suspects the warm start to winter might have helped tick survival. But, like some health officials, she suggests that if her dogs are infected, it likely signals a problem for humans.
High numbers: According to the state Department of Health, York County is among the worst in the state when it comes to Lyme disease. In 2005, 386 county residents tested positive for the disease, which initially mimics flu symptoms such as headache and fatigue.
The number of human cases for 2006 is not yet available; state departments of health and agriculture do not track the disease in animals. Still, health department spokesman Richard McGarvey says humans should remain cautious.
Lyme disease is caused by bacteria called Borrelia burgdorferi, and if left untreated can spread to joints, the heart and nervous system. The disease is transmitted to animals and humans by infected blacklegged ticks, also known as deer ticks.
Veterinarian Erich Hoffman of Shiloh Animal Hospital said area vets have seen a marked increase in pets testing positive for the disease in the past two years. He said that's due to a ramped-up test for heartworm, which also tests for Lyme, and increased deer tick population.
"One of 10 dogs test positive for Lyme," Hoffman said. He explained that while many test positive, all do not get sick or show symptoms. Still, he said, a month hasn't passed when area vets don't find ticks -- of various types -- on dogs and cats.
Unlike for humans, there are vaccines for dogs for about $20. And dogs that have contracted the disease can be treated successfully with antibiotics. Lyme is fatal for some dogs if the disease attacks the kidneys, causing them to fail.
Hoffman advises pet owners to look for symptoms such as flu-like symptoms, joint pain and fatigue. As in humans, these symptoms are typical of Lyme.
Incubation time: While he said it's more common to see dogs with Lyme in the fall, vets still are unsure what the incubation time for the disease from bite to onset. In laboratories, that's usually three to five months.
"In the wild, we honestly don't know," he said.
As for animals signaling a bigger problem for humans, Hoffman said he's not sure.
"Dogs probably are more likely to contract ticks than (humans) are because they run through the briars," he said. "Whereas humans tend to walk on the path." But McGarvey, who lives in York County, said he takes precautions every time he is in tick-prone areas and advises fellow residents to do the same.
Deer ticks congregate in tall grass and brush, such as that found near Klinedinst's home in Lower Windsor Township.
And the ticks are minuscule, often no bigger than the head of a pin.
"Most people think they're like dog ticks, the big ones that you would feel walking on you," McGarvey said. "You can't even feel these crawl across your skin."
He advises residents to take a few minutes every time they come indoors from tick-prone areas to take five minutes for the "tick check."
Look for black dots on the skin or on the scalp; also, check for the bulls-eye shaped rash associated with the deer tick bite. Those who've been bitten are advised to see a doctor.
"It's worth five minutes to check your hair and skin," he said. "(Lyme) is treatable if it's caught early."
Reach Kathy Stevens at 505-5437 or kstevens@yorkdispatch.com.
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© 2006 The National Lyme Disease Memorial Park Project
