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Ticked off: Sequencing of deadly cattle tick’s genome leads to new vaccine

Image of a sign saying "Cattle Tick Free Area"We have good reason to pay attention to the tiny, flightless, blood-sucking tick. Measuring as small as 1-2mm in their early life stage, they are virtually unnoticeable in fur, hair, or at the tip of grass leaves where they often gather to ambush an animal, bird or human host. Like it’s winged cousin, the mosquito, ticks are vectors of blood-borne disease – as many as 60 different illnesses are transmitted by ticks, some of which are common to both humans and livestock.

So severe are its impacts on livestock that this unassuming insect was the target of a county-wide eradication of one of their species, the southern cattle tick (Rhipicephalus [Boophilus] microplus), in the United States in the mid 1900s. Even though its occurrence in the US remains extremely low – it’s hard to control an insect that can hurdle across the Rio Grande (the US-Mexico border) on the back of a deer after all – it continues to transmit diseases to cattle in tropical and subtropical regions that cost billions upon billions each year.

These costs, along with decreasing efficacy of the drugs that have been used to treat tick-borne diseases prompted an American-led research team to dig into the southern cattle tick’s large genome (about 2.5 times larger than the human genome) in search of a possible target for a vaccination-based approach. As reported this month in the journal Parasites & Vectors, they found it, in the form of a protein that helps the tick excrete the large quantities of water it consumes as part of its blood meal. Following two trials of the developed vaccine that lead author Felix Guerrero said showed a “a 75-percent and 68-percent reduction in the number of ticks on vaccinated 1-year-old Holstein calves,” the team is reportedly now working with a company to commercialize the product.

Assuming this venture is successful, this will be a great boon to cattle farmers the world over – and to their animals, 80 percent of which will contract a tick-borne illness during their lifespan. Many of these illnesses are relatively benign or easily treatable, however two, babesiosis and anaplasmosis, are considered to be the most devastating in terms of risk of animal mortality, reduced beef and milk production and trade restrictions. Humans can also contract variant strains of babeiois and anaplasmosis, which are carried by different vector ticks of the Ixodes genus – the same culprits responsible for Lyme disease.

While tropical and subtropical countries are most affected by tick-borne disease in cattle, due to the common range of carrier ticks, livestock in northern or more temperate zones are also at risk. Sporadic incidences of babesiosis and anaplasmosis have been recorded in Canada. It is highly unlikely that these incidences came from the southern cattle tick – the anaplasmosis bacteria has as many as 20 different tick vectors, some of which are common in Canada, and the traffic of cattle and other animals across borders is often seen as a route for disease spread. However, in recent decades, the documented spread of another species of tick, the black-legged or deer tick (Ixodes scapularis), into larger Canadian ranges, particularly in the east and central regions of the country, along with other research on the effects of climate change on biodiversity and insect survival suggest that tick-borne diseases are slowly spreading north.

In 2012, an Alberta survey of more than 800 animal hosts (mostly dogs) netted 16 different species of tick in the province, including two that had not previously been known to exist within provincial boundaries (it was undetermined whether these newcomers were established in the province, but were thought likely acquired during travels outside Alberta). A provincial surveillance program in place since 2007, expanded in 2013 and 2014, collects information on ticks found on companion animals, livestock and in the wild as a means to track the disease pathogens.

Much of the surveillance has been prompted by concerns over Lyme disease, the better-known tick-borne blood illness that is common to humans and dogs but also found in a variety of other animals, including cattle and horses on occasion. As more ticks are collected and analysed, the tracking may help identify patterns and changes in tick habitat and incidence of pathogens for future study and disease control.

Photo credit: Tony Bowden, Flickr

Ticked off: Sequencing of deadly cattle tick’s genome leads to new vaccine

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