Bloodsucking invaders: Is the devil you know better than the one you don't?

A guest post by Heather Kopsco, Ph.D. Candidate at the University of Rhode Island:

          Just outside Houston, Texas, the hazy early morning light dissolved into a warm orange glow as a port worker began his shift. He climbed high into the worn seat of a fork lift and started the engine. The tired belts hummed, drowning out the sound of grating gears as he exited the garage bay toward a multicolored skyscraper of containers. He didn’t know what was in the shipment, just that the three red containers on the top of the stack needed to be inspected. He pulled a lever to lift the goal-post-sized fork beneath the bottom of the container and lowered the first one to the ground. A U.S. customs inspector stood waiting below, clipboard in hand to check off the contents of the container. He forced open the container’s lock bar and swung open the heavy metal door, spilling morning light into the container. “Used tires,” he mumbled, and scribbled his initials onto the inspection sheet. He selected an easily accessible stack, wrapped in tightly molded clear plastic, and casually sliced into the packaging. As he examined the stacks of black rubber and recorded identification numbers, out flew dozens of black and white striped insects from deep inside the sidewalls, unnoticed. “All good here,” the inspector declared, and slammed the door closed. Later that day, the shipment of tires headed to distribution centers throughout the country.

            The tire stowaway, commonly known as the Asian tiger mosquito (Aedes albopictus), is now considered to be one of the 100 world’s worst invasive species per the Global Invasive Species Database¹. At the time of its detection in the United States back in the mid-1980s, experts were worried because the insect transmits viruses like dengue, yellow fever, chikungunya, and eastern equine encephalitis in other parts of the world. Would this mosquito locally acquire and spread these diseases throughout the warmer parts of the U.S.? How far could it travel, survive, and reproduce? There were so many questions.

           

            Over the course of around three decades, the tiger mosquito spread to 40 states, and the Centers for Disease Control and Prevention (CDC) anticipate changes in climate will allow it to thrive even further north of where it currently resides^6,2. It was, and still is, of medical concern because it bites throughout the day rather than at night, it can breed quickly and easily in tiny amounts of water trapped in containers found commonly around where humans live, and it can out-compete and even eradicate other mosquito species that may not pose as much of a disease risk². Fortunately, only small, isolated outbreaks of dengue and chikungunya have occurred, mainly along the Gulf Coast or in U.S. islands². Fear of this mosquito reignited in 2015 during the Zika virus epidemic since it is one of the mosquitoes responsible for spreading the disease in South America, and there was concern that it could spread it here. Only a handful of locally transmitted cases occurred, but the renewed attention led to a resurgence in Congressional funding for overall mosquito control research so that we would be ready to address and hopefully prevent larger outbreaks².

Figure 1. Asian tiger mosquito (Aedes albopictus) (top). Estimated potential range of the Asian tiger mosquito (Aedes albopictus), 2017 (bottom)¹

            We’re seeing a similar story emerge around the newly-detected invasive Asian longhorned tick (Haemaphysalis longicornis). It was first identified in November 2017 on a farm in Hunterdon, New Jersey when the owner reported an abnormally large tick burden on her pet sheep and within its paddock³. Local entomologists soon recognized the offending parasites as Haemaphysalis longicornis – the Asian longhorned tick – native to east Asia³. But to add to the intrigue, the sheep had never traveled, so the origin of this tick infestation was a mystery³. Since that initial discovery, the Asian longhorned tick has been reported in ten states (Fig. 2), and found feeding on a wide diversity of animals including cattle, horses, deer, sheep, pigs, goats, raccoon, opossum, dogs, cats, and humans⁴. Very few males have been found, even among large infestations, leading researchers to believe that this invader reproduces parthenogenically, in other words, female longhorned ticks are capable of cloning themselves without the help of a male³. Reexamination of historical tick records revealed that the longhorned tick was often mistaken as a rabbit tick, and was actually present in the U.S. since 2010⁴. One thought on its introduction is that it hitched a ride to the U.S. on dogs rescued from overseas meat markets, because while these animals are required to have rabies vaccinations, they are not routinely checked for parasites like ticks. But this story is merely speculation at this point.                 

            

Figure 2. Current known range of the Asian longhorned tick (Haemaphysalis longicornis) (top)⁴. Asian longhorned ticks (Adult female, nymph, larvae) (bottom)³               

            
            Similar to the case of the tiger mosquito, we are not yet sure what diseases this tick will be capable of transmitting, if any. In its native range, the longhorned tick is a major livestock pest and can also cause serious illness in humans. It transmits babesiosis and bovine theileriosis blood parasites to cattle, and large infestations can very quickly bleed herds to the point of anemia or even death^3,4. As far as humans pathogens go, this tick is also known to transmit anaplasma, ehrlichia, Powassan virus, and Severe Fever with Thrombocytopenia Syndrome virus, all diseases that can cause serious or deadly illness^3,4. The good news is that, to date, none of the ticks found in the U.S. have tested positive for any human or animal diseases. Researchers at the CDC are currently working with a colony of longhorned ticks in a lab to learn which of the tick borne diseases we have here in the U.S. this tick may be able to pick up through feeding and be able to transmit to other animals or to humans. Anecdotal evidence demonstrates that these ticks are not fans of feeding on rodents, which suggests that they are unlikely to pick up diseases like Lyme and babesia, which are maintained in nature by these small mammals.

           

            While ticks obviously do not have the same travel capabilities as mosquitoes, they certainly get around. The longhorned tick’s wide host preference increases the likelihood that it will spread since it is found on large mammals with wide home ranges, like deer, but also recently on a dog that traveled from New York state (where it is established) to New Hampshire, and on a hawk in Virginia. Entomologists are particularly concerned that, while its establishment throughout the country will likely be limited by its strict humidity requirements, the longhorned tick appears to be cold-tolerant and less susceptible to the go-to-tick-killing pesticide permethrin than are native tick species³. On the ground-zero farm, larvae reemerged the following spring after both a hefty treatment of permethrin on the property and a long, cold New Jersey winter³. Longhorned ticks appear to be highly adaptable, and given their successful invasions in other countries like Australia and New Zealand³, they’re likely here to stay.

            So what do we do with this information, or rather, lack of information? Similar to the case of the tiger mosquito, it’s important to know enough about this new invader so that it can be reported local entomologists, but to also protect yourself from bites. Since we do not know where, when, or if this tick will develop the ability to transmit our local diseases, it’s important to diligently perform tick checks on both humans and pets after time out in tick habitat. This tick seems to prefer edge habitat along grassy meadows and forests where it has access to numerous wildlife hosts, and has the potential to be active during warmer days in the winter, given its cold tolerance. Pets should be protected year-round with a veterinarian-approved tick preventative product to prevent bites, as well as accidental tick introduction to the home or new locations during travel.

           

            Just as with efforts to monitor the tiger mosquito, citizen-scientists can offer powerful, effective, and wide-spread surveillance⁵. The University of Rhode Island maintains TickSpotters, a highly-accurate photo-based tick ID system that provides a risk assessment and customized prevention suggestions in response to a quality photograph of an encountered tick. The system has already received reports that have detected the longhorned tick in several of the established states. If you find any tick, but particularly one you think might be the longhorned tick, please report it to TickSpotters. As they say, a good photo of a longhorned tick in the hand is worth two in the bush.

           

 References:

1. Global Invasive Species Database. 2018. “Species profile: Aedes albopictus.” Downloaded from http://www.iucngisd.org/gisd/species.php?sc=109 on 10-11-2018.

2. Moreno-Madriñán MJ, Turell M. History of Mosquitoborne Diseases in the United States and Implications for New Pathogens. 2018. Emerging Infectious Diseases. 24(5):821-826.

3. Rainey T, Occi JL, Robbins RG, Egizi A. 2018. Discovery of Haemaphysalis longicornis(Ixodida: Ixodidae) Parasitizing a Sheep in New Jersey, United States. Journal of Medical Entomology. 55(3): 757–759. https://doi.org/10.1093/jme/tjy006

4. United States Department of Agriculture Animal and Plant Health Inspection Service. 2018. “Longhorned Tick: Information for Livestock and Pet Owners.” Downloaded from: https://www.aphis.usda.gov/publications/animal_health/fs-longhorned-tick.pdf.

5. Palmer JRB,  Oltra A, Collantes F, 4, Delgado JA, Lucientes J, Delacour S, Bengoa M, Eritja R, and Bartumeus F. 2017. Citizen science provides a reliable and scalable tool to track disease-carrying mosquitoes. Nature Communications. 8(916): 1-13.

6. Hahn MB, Eisen L, McAllister J, Savage HM, Mutebi J-P, Eisen RJ. 2017. Updated Reported Distribution of Aedes (Stegomyia) aegypti and Aedes (Stegomyia) albopictus (Diptera: Culicidae) in the United States, 1995-2016. Journal of Medical Entomology. 54(5): 1420-1424.