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Vaccines to Battle Tick Diseases?

 I recently posted on ways the number of  ticks can be reduced in a backyard. Now an article on vaccines being developed to battle tick borne diseases, especially Lyme disease. However, the bad news is that ticks now transmit 16 diseases in the US (including anaplasmosis, babesiosis, ehrlichiosis), while vaccines typically only focus on one disease at a time. Tick borne diseases are on the rise throughout the world. We all know about Lyme disease (which is also a problem in Europe, China, and Mongolia), but in parts of Africa, the Middle East, Asia and southern Europe, ticks can spread Crimean–Congo haemorrhagic fever, which is fatal 40% of the time! And while some researchers are focusing on human vaccines, some are focusing on vaccines for mice. Big problem: would we really be able to give the vaccine to enough mice to make a difference? I really like the idea of a vaccine that hampers the ability of ticks to feed on humans. From Nature:

The new war on Lyme and other tick-borne diseases

Williams is testing whether vaccinating mice against Borrelia burgdorferi, the bacterium that causes Lyme disease in the United States, can reduce the proportion of ticks that are infected. ....Borrelia burgdorferi infects an estimated 329,000 people in the United States each year, according to the US Centers for Disease Control and Prevention (CDC) in Atlanta, Georgia. And although most people who get prompt treatment recover quickly — Williams has had Lyme three times — up to one in five develops long-term and potentially life-threatening symptoms, including heart, vision or memory problems, or debilitating joint pain.

Williams's approach is one of several strategies being tested in an attempt to thwart the spread of tick-borne diseases. Some, like the mouse vaccine, interrupt the pathogen's ecological circuitry by targeting the wild animals that pass along and amplify the disease. Others, such as efforts to revive a human Lyme vaccine, aim to protect people from infection directly. A more radical approach could hamper the ability of ticks to bite humans or animals, potentially protecting against dozens of illnesses spreading across the United States, Europe, Africa and Asia.

That the field needs creative solutions is clear. Many long-recommended interventions, such as pesticide application or controlling populations of deer, which are an important host for adult ticks, have had mixed success in scientific studies. Even the time-honoured protective strategies that most people use are not evidence-based. “We tell people to wear repellents, to do tick checks and to shower if they've been in the field, but there's very little data to show that these things reduce human illness,” explains Ben Beard, chief of the CDC's bacterial-diseases branch in the division of vector-borne diseases.

The plan is unconventional, because most Lyme-control measures focus on white-tailed deer (Odocoileus virginianus), which have exploded in number in the United States over the past century as young forests have become increasingly fragmented by human development and large predators have been all but eradicated. Adult blacklegged ticks (Ixodes scapularis) typically feed and mate on deer, so many scientists have argued that the only way to get rid of Lyme is to get rid of the deer. But such efforts have had “an incredibly spotty record”, says Richard Ostfeld, a disease ecologist at the Cary Institute of Ecosystem Studies in Millbrook, New York, who has been studying tick-borne diseases for decades.

Ostfeld and others contend that mice are a major driver for both the tick problem and the disease problem. Mice, like deer, flourish in fragmented woodlands — in part because predators such as foxes and opossums get displaced. Ticks then thrive on the rodents, which are poor groomers. Studies suggest that larval ticks have a 50% chance of surviving when they feed on mice, but only a 3.5% chance on opossums2.

And mice are typically where ticks pick up B. burgdorferi. Most mice in Lyme-endemic areas get infected with the bacterium at a young age and, for reasons that are not completely clear, they are particularly good at transmitting it to other ticks. Almost all young ticks that feed on white-footed mice become infected, compared with a mere 1% of ticks that feed on deer. Interrupting the tick–mouse infection cycle, says Ostfeld, could make ticks a lot less dangerous.... The bait-based vaccine is also attractive because it is less ecologically destructive than other strategies — it does not kill animals or even ticks, just the pathogens.

Other scientists argue for more a direct means of protecting people against Lyme, ideally with a human vaccine. ....product called LYMErix, manufactured by UK-based pharmaceutical company SmithKline Beecham (now GlaxoSmithKline), was approved by the US Food and Drug Administration in 1998. It reduced the risk of Lyme caused by US strains of Borrelia by 76% in clinical trials4. But it faced problems from the start....The company voluntarily shelved LYMErix in 2002. Plotkin maintains that this was a mistake. “The vaccine was safe,” he says.

Now, a new and potentially improved vaccine has completed safety trials5. Developed by researchers at Stony Brook University and Brookhaven National Laboratory in New York, and licensed to Baxter Innovations in Vienna... it protects against many Borrelia species known to cause Lyme in humans, including those that affect people in Europe....Richard Marconi, a microbiologist and vaccinologist at Virginia Commonwealth University in Richmond, says that he and his colleagues are working on an even better vaccine.

Mouse vaccines would not raise such concerns, but some researchers, including Plotkin, are sceptical about whether they could dose enough mice to reduce Lyme rates. And both vaccine approaches are limited because they combat only one tick-borne disease, when more than a dozen others are spreading throughout the world (see 'Reality bites').

There is one strategy that could conquer them all, and it involves turning one of the tick's most ingenious tools — its saliva — against it. When a tick bites a host, molecules in its saliva help it to evade detection and start to feed by blocking pain, inflammation and immune signals. If a vaccine could raise an immune response to key salivary proteins, it could make tick bites more noticeable or block the tick's ability to feed. Ostfeld himself is a proof-of-concept for this approach. He has been bitten more than 100 times, and his body now reacts to tick saliva. “I realize when a tick is biting me because I get a burning sensation. It's pretty intense,” he explains. 

A European Commission-funded consortium called ANTIDotE (Anti-tick Vaccines to Prevent Tick-borne Diseases in Europe) is characterizing the tick salivary proteins that could be targeted to thwart feeding. “We think that an anti-tick vaccine could be immensely useful in protecting both humans and animals,” says Hein Sprong, an ANTIDotE leader at the National Institute for Public Health and the Environment in Bilthoven, the Netherlands. US Biologic also plans to develop a bait-based vaccine for mice that could thwart tick feeding, thereby protecting against multiple diseases. That could reduce overall tick numbers, too, because it would make it difficult for larval ticks to get the meals that they need to survive into adulthood and reproduce.

But these approaches are hardly around the corner. Part of the problem, scientists say, is that funding is scarce. The stereotype of Lyme and other US tick-borne diseases as primarily 'yuppie' illnesses does not help;... Until an all-encompassing solution becomes available, controlling tick-borne diseases will probably require an array of smaller-scale approaches that attack the problem, bit by bit, on a number of levels. 

 Deer can harbor many engorged ticks behind their ears; the ticks drop off in areas where the deer pass through or rest. Credit: Peter Priolo

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