Tick-borne diseases are a serious health threat, not only in the United States, but in other regions of the world, and because of a warming planet, medical experts around the globe are taking a serious look at a number of vector-borne diseases and their threat of spreading geographically.
In the U.S., a comprehensive study based on 19 years of data collected at the Cary Institute of Ecosystem Studies in Millbrook, N.Y. has shown that warming temperatures have influenced not only the earlier emergence of ticks, but their spread to new regions. The findings were published in the journal Philosophical Transactions of the Royal Society B: Biological Sciences, on February 16, 2015.
Located in Dutchess County in New York’s mid-Hudson Valley, the 2,000-acre the Cary Institute research campus is the ideal location to study the black-legged tick because it sits at ground-zero for tick-borne diseases. Besides the campus buildings, the grounds are a living laboratory for field research, with lowlands, ponds, creeks, hiking trails through dense forests, and an extensive display of native flora and fauna.
Dr. Richard S. Ostfeld, the co-author of the study summed things up well, saying, “Nearly two decades of data revealed climate warming trends correlated with earlier spring feeding by nymphal ticks, sometimes by as much as three weeks. If this persists, we will need to move Lyme Disease Awareness Month from May to April.”
Dr. Ostfeld went on to explain the complicated interaction between pathogens, ticks and their host animals that takes place. For black-legged ticks, they pick up the bacterium, Borrelia burgdorferi when they feed on small mammals that are harboring the pathogen. Not only that, but amazingly, the tick seeks a single blood meal at each stage of its life. This includes larva, nymph, and adult stages. So this means the larval stage of the tick is free of B. burgdorferi. Ostfeld says the nymphs pose the biggest threat to people.
What stage of life ticks are in is necessary to predicting tick-borne disease spread said Dr. Taal Levi of Oregon State University, who was working with Ostfeld, doing emergence studies. ” Pathogens that cause a lasting host infection, such as the Lyme disease bacterium, benefit from a lag between nymphal and larval feeding,” Dr. Levi pointed out. This isn’t true of other tick-borne diseases like the Powassan virus, because it is transmitted when the nymphs and larvae are feeding at the same time.
For the observations conducted in the study, more than 53,000 mice, 12,000 chipmunks, 403,000 larval ticks and 44,000 nymphal ticks collected in the Cary Institute’s forests. The team found that the numbers of nymphs peaked in the spring, and larvae in the summer. It was found that both the nymphs and larvae peaked three weeks earlier during warmer years, but they never converged, or peaked at the same time.
Dr. Ostfeld emphasized, “Here in the Northeast, warming is already having an effect, and people need to be tick-vigilant before May, as potentially infected nymphal ticks are searching for their blood meals earlier and earlier.” Additionally, clear evidence was found that warming temperatures were helping to expand the tick population to higher latitudes as well as altitudes. The research team acknowledged that more work was needed to fully understand how and why differences in the environment in different regions influenced the expansion of some tick populations and not others.
