For the first time in 50 years, a new tick species has arrived in the United States — one that in its Asian home range carries fearsome diseases.

The Asian long-horned tick, Haemaphysalis longicornis, is spreading rapidly along the Eastern Seaboard. It has been found in seven states and in the heavily populated suburbs of New York City.

At the moment, public health experts say they are concerned, but not alarmed.

Although domestic American ticks are a growing menace and transmit a dozen pathogens, no long-horned ticks here have yet been found with any human diseases. In Asia, however, the species carries a virus that kills 15 percent of its victims.

For now, the new arrivals are considered a greater threat to livestock.

Known in Australia as bush ticks and in New Zealand as cattle ticks, long-horned ticks can multiply rapidly and suck so much blood from a young animal that it dies. The ticks bloat up like fat raisins until their tiny legs are barely able to support them.