Ticks Spread Plenty More for You to Worry About Beyond Lyme Disease
By Jerome Goddard
When it comes to problems caused by ticks, Lyme disease hogs a lot of the limelight. But various tick species carry and transmit a collection of other pathogens, some of which cause serious, even fatal, conditions.
In fact, the number of tick-borne disease cases is on the rise in the U.S. The range where various species of ticks live in North America may be expanding due to climate change. Researchers continue to discover new pathogens that live in ticks. And new, invasive tick species keep turning up.
In my career as a public health entomologist, I've been amazed at the ability of ticks to bounce back from all the ways people try to control them, including with pesticides. Ticks excel at finding new ecological niches for survival. So people and ticks frequently cross paths, exposing us to their bites and the diseases they carry.
Here are some of the lesser-known, but growing, threats from ticks.
Ticks Can Spread Bacterial Diseases
Certain very small species of bacteria that can cause human diseases, such as rickettsia, ehrlichia and anaplasma, live in ticks. Ticks ingest these bacteria when they drink animals' blood. Then when the ticks take a subsequent blood meal, they pass the bacteria along to the next animal or person they feed on.
Probably the most well known of these bacterial diseases is Rocky Mountain spotted fever, the most frequently reported rickettsial disease in the U.S., with about 6,000 cases each year. The number of diagnoses seems to be increasing nationwide, especially among Native Americans, probably due to exposure on reservations to free-roaming dogs that can carry ticks.
Rocky Mountain spotted fever usually comes with a rash, as on this child.
Centers for Disease Control and Prevention, National Center for Immunization and Respiratory Diseases (NCIRD), CC BY
When people get sick with Rocky Mountain spotted fever, they usually come to a clinic with three things: fever, rash and history of tick bite. They may also report severe headache, chills and muscle pains, and gastrointestinal symptoms such as abdominal pain and diarrhea. A skin rash is usually present after a few days, but not always. Mental confusion, coma and death can occur in severe cases. Untreated, the mortality rate is about 20%; and even with treatment, 4% of those infected die.
Not all tick species are effective transmitters of the rickettsia bacteria. Even within the vector species, often only 1% to 5% of ticks in an area are infected. So getting bitten by a tick that passes rickettsia bacteria on to you is like getting stuck with a needle in a haystack. The primary carriers are the American dog tick in the eastern U.S. and Rocky Mountain wood tick in the West. The brown dog tick has also recently been shown to be a vector.
In most tick-borne diseases, the tick needs to feed for some amount of time before any pathogens it is carrying are transmitted to the animal whose blood it is eating. Rocky Mountain spotted fever organisms generally take between one and three hours for transmission to occur, so attached ticks need to be removed quickly. Doctors usually prescribe the antibiotic doxycycline to treat Rocky Mountain spotted fever, which works quite well if the disease is recognized early.
Ehrlichiosis is another bacterial disease transmitted from ticks to people. In the U.S. it's most commonly caused by Ehrlichia chaffeensis bacteria, carried by lone star ticks which are common in the eastern U.S. Ehrlichia bacteria infect a type of blood cell called leukocytes. Human monocytic ehrlichiosis occurs mostly in the southern and south-central U.S.; 1,642 cases were reported to the CDC in 2017.
Ehrlichiosis patients usually have fever, headache, muscle aches and a progressive low white blood cell count. As opposed to Rocky Mountain spotted fever, people get a rash only about 20% to 40% of the time. Doctors usually treat ehrlichiosis with doxycycline.
Another tick-borne bacterial disease to worry about is human granulocytic anaplasmosis. In human granulocytic anaplasmosis, Anaplasma phagocytophilum bacteria infects a type of white blood cell called granulocytes. It mostly occurs in the upper midwestern and northeastern U.S., and the incidence is increasing, with 5,762 cases of human granulocytic anaplasmosis reported to the CDC in 2017.
Symptoms include fever, headache, muscle aches and progressive low white blood cell count. It's the deer tick Ixodes scapularis — famously also responsible for Lyme disease — that transmits the Anaplasma bacteria to humans. There's the unlucky chance that a bite from a deer tick could infect you with both diseases. Again, recommended therapy is doxycycline.
A female Ixodes scapularis tick.
Dr. Blake Layton, MSU, CC BY-ND
Ticks Can Carry Viruses, Too
People usually think of mosquitoes when they think of insect-transmitted viruses – dengue, Zika or West Nile garner a lot of headlines. But ticks can transmit viruses, too.
Scientists have historically grouped tick-borne viral diseases into two categories. One is diseases similar to dengue fever. The main dengue-like viral disease transmitted by ticks in the U.S. is Colorado tick fever, which occurs in mountainous areas of the West.
The other group of tick-borne diseases resemble mosquito-borne encephalitis. Most of these illnesses, characterized by brain inflammation, are not found in the U.S. Powassan encephalitis is the one that is, occurring in the northeastern U.S. and adjacent regions of Canada.
Powassan is a relatively rare but serious human disease, characterized by sudden onset of fever with temperature up to 104 degrees Fahrenheit, along with convulsions. Brain inflammation is usually severe, with vomiting, respiratory distress and prolonged fever.
Fewer than 100 cases of Powassan have been reported in North America, with about half of them fatal. Its incidence seems to be increasing; there were 34 cases of Powassan reported during 2017. POW is maintained in a natural cycle when ticks — primarily Ixodes cookei — infect animals with the virus via their bites. Then these infected animals may serve as what scientists call disease reservoirs, infecting new ticks when they feed on their blood.
Tiny larval lone star ticks next to a penny.
In the last decade, researchers have found additional new tick-borne viruses in the U.S. About 30 cases of Heartland virus have thus far been identified. It's associated with the lone star tick and has been recognized in Missouri, Oklahoma, Kentucky and Tennessee.
A few cases of a new Thogotovirus called Bourbon virus have been identified in the Midwest and southern U.S. The lone star tick may be the vector of Bourbon virus as well.
A Food Allergy Triggered by a Tick Bite
Maybe the most bizarre threat from ticks is the "red meat allergy" scientists have recently traced back to tick bites. People can become allergic to eating meat when a tick's saliva passes on the carbohydrate galactose-α-1.3-galactose it had previously picked up in a blood meal from an animal. If prone to allergies, the person can get sensitized to that alpha-gal molecule that's found in animal blood and other tissues.
Then days or weeks later, he or she may develop hives, swollen skin and lips, or even life-threatening anaphylactic shock three to six hours after eating red meat. Meats containing alpha-gal include beef, pork, lamb, squirrel, rabbit, horse, goat, deer, kangaroo, seal and whale. People who become sensitized to alpha-gal may still eat chicken, turkey and fish.
Overall, people should be aware of what tick-borne diseases are present in their area and use personal protection techniques whenever outdoors in tick-infested areas. Remember that ticks often come into close contact with people via pet dogs or cats. It's a good idea to inspect yourself for ticks after being outdoors in tick-infested areas. Reducing the number of tick bites and the amount of time ticks remain attached can go a long way to protecting you from tick-borne diseases.
Invasive Tick Spreads to Ninth State, CDC Warns of 'New and Emerging Disease Threat' https://t.co/9r4yqpJvxJ— EcoWatch (@EcoWatch) December 3, 2018
Jerome Goddard is an extension professor of biochemistry, molecular biology, entomology and plant pathology at Mississippi State University.
Disclosure statement: Jerome Goddard does not work for, consult, own shares in or receive funding from any company or organization that would benefit from this article, and has disclosed no relevant affiliations beyond his academic appointment.
Reposted with permission from our media associate The Conversation.
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By Melissa Gaskill
Two decades ago scientists and volunteers along the Virginia coast started tossing seagrass seeds into barren seaside lagoons. Disease and an intense hurricane had wiped out the plants in the 1930s, and no nearby meadows could serve as a naturally dispersing source of seeds to bring them back.
Restored seagrass beds in Virginia now provide habitat for hundreds of thousands of scallops. Bob Orth, Virginia Institute of Marine Science / CC BY 2.0<p>The paper is part of a growing trend of evidence suggesting seagrass meadows can be easier to restore than other coastal habitats.</p><p>Successful seagrass-restoration methods include <a href="https://www.sciencedirect.com/science/article/abs/pii/S0304377099000078?via%3Dihub" target="_blank">transplanting shoots</a>, <a href="https://onlinelibrary.wiley.com/doi/10.1111/j.1061-2971.2004.00314.x" target="_blank" rel="noopener noreferrer">mechanized planting</a> and, more recently, <a href="https://www.nature.com/articles/s41467-020-17438-4" target="_blank" rel="noopener noreferrer">biodegradable mats</a>. Removing threats, proximity to donor seagrass beds, planting techniques, project size and site selection all play roles in a restoration effort's success.</p><p>Human assistance isn't always necessary, though. In areas where some beds remain, seagrass can even recover on its own when stressors are reduced or removed. For example, seagrass began to recover when Tampa Bay improved its water quality by reducing nitrogen loads from runoff by roughly 90%.</p><p>But more and more, seagrass meadows struggle to hang on.</p><p>The marine flowering plants have declined globally since the 1930s and currently disappear at a rate equivalent to a football field every 30 minutes, according to the <a href="https://www.unep.org/resources/report/out-blue-value-seagrasses-environment-and-people" target="_blank" rel="noopener noreferrer">United Nations Environment Programme</a>. And research published in 2018 found the rate of decline is <a href="https://agupubs.onlinelibrary.wiley.com/doi/full/10.1029/2018GB005941" target="_blank" rel="noopener noreferrer">accelerating</a> in many regions.</p><p>The causes of decline vary and overlap, depending on the region. They include thermal stress from climate change; human activities such as dredging, anchoring and coastal infrastructure; and intentional removal in tourist areas. In addition, increased runoff from land carries sediment that clouds the water, blocking sunlight the plants need for photosynthesis. Runoff can also carry contaminants and nutrients from fertilizer that disrupt habitats and cause algal blooms.</p><p>All that damage comes with a cost.</p>
The Value of Seagrass<p>As with ecosystems like rainforests and <a href="https://therevelator.org/mangroves-climate-change/" target="_blank">mangroves</a>, loss of seagrass increases carbon dioxide emissions. And that spells trouble not just for certain habitats but for the whole planet.</p><p>Although seagrass covers at most 0.2% of the seabed, it <a href="https://www.unenvironment.org/news-and-stories/story/seagrass-secret-weapon-fight-against-global-heating" target="_blank">accounts for 10%</a> of the ocean's capacity to store carbon and soils, and these meadows store carbon dioxide an estimated 30 times faster than most terrestrial forests. Slow decomposition rates in seagrass sediments contribute to their <a href="https://www.researchgate.net/publication/238506081_Assessing_the_capacity_of_seagrass_meadows_for_carbon_burial_Current_limitations_and_future_strategies" target="_blank" rel="noopener noreferrer">high carbon burial rates</a>. In Australia, according to <a href="https://onlinelibrary.wiley.com/doi/10.1111/gcb.15204" target="_blank" rel="noopener noreferrer">research</a> by scientists at Edith Cowan University, loss of seagrass meadows since the 1950s has increased carbon dioxide emissions by an amount equivalent to 5 million cars a year. The United Nations Environment Programme reports that a 29% decline in seagrass in Chesapeake Bay between 1991 and 2006 resulted in an estimated loss of up to 1.8 million tons of carbon.</p>
Eelgrass in the river delta at Prince William Sound, Alaska. Alaska ShoreZone Program NOAA / NMFS / AKFSC; Courtesy of Mandy Lindeberg / NOAA / NMFS / AKFSC<p>Seagrasses also protect costal habitats. A healthy meadow slows wave energy, reduces erosion and lowers the risk of flooding. In Morro Bay, California, a 90% decline in the seagrass species known as eelgrass caused extensive erosion, according to a <a href="https://www.sciencedirect.com/science/article/abs/pii/S0272771420303528?via%3Dihub" target="_blank" rel="noopener noreferrer">paper</a> from researchers at California Polytechnic State University.</p><p>"Right away, we noticed big patterns in sediment loss or erosion," said lead author Ryan Walter. "Many studies have shown this on individual eelgrass beds, but very few studies looked at it on a systemwide scale."</p><p>In the tropics, seagrass's natural protection can reduce the need for expensive and often-environmentally unfriendly <a href="https://www.nioz.nl/en/news/zeegras-spaart-stranden-en-geld" target="_blank" rel="noopener noreferrer">beach nourishments</a> regularly conducted in tourism areas.</p><p>Seagrass ecosystems improve water quality and clarity, filtering particles out of the water column and preventing resuspension of sediment. This role could be even more important in the future. By producing oxygen through photosynthesis, meadows could help offset decreased oxygen levels caused by warmer water temperatures (oxygen is less soluble in warm than in cold water).</p><p>The meadows also provide vital habitat for a wide variety of marine life, including fish, sea turtles, birds, marine mammals such as manatees, invertebrates and algae. They provide nursery habitat for <a href="https://wedocs.unep.org/bitstream/handle/20.500.11822/32636/seagrass.pdf?sequence=1&isAllowed=y" target="_blank" rel="noopener noreferrer">roughly 20%</a> of the world's largest fisheries — an <a href="https://www.floridamuseum.ufl.edu/science/seagrass-meadows-harbor-wildlife-for-centuries/" target="_blank" rel="noopener noreferrer">estimated 70%</a> of fish habitats in Florida alone.</p><p>Conversely, their disappearance can contribute to die-offs of marine life. The loss of more than 20 square miles of seagrass in Florida's Biscayne Bay may have helped set the stage for a widespread <a href="https://www.wlrn.org/2020-08-14/the-seagrass-died-that-may-have-triggered-a-widespread-fish-kill-in-biscayne-bay" target="_blank">fish kill</a> in summer 2020. Lack of grasses to produce oxygen left the basin more vulnerable when temperatures rose and oxygen levels dropped as a result, says Florida International University professor Piero Gardinali.</p>
Damaged Systems, a Changing Climate<p>Governments and conservationists around the world have already put a lot of effort into coastal restoration efforts. And that's helped some seagrass populations.</p><p>Where stressors remain, though, restoration grows more complicated. <a href="https://www.rug.nl/research/portal/en/publications/the-future-of-seagrass-ecosystem-services-in-a-changing-world(3a8c56db-7bed-4c9e-ac7f-c72453e2a102).html" target="_blank">Research</a> published this September found that only 37% of seagrass restorations have survived. Newly restored meadows remain vulnerable to the original stressors that depleted them, as well as to storms — and <a href="https://www.ecowatch.com/tag/climate-crisis">climate change</a>.</p>
Seagrass in Dry Tortugas National Park, Florida. Alicia Wellman / Florida Fish and Wildlife / CC BY-NC-ND 2.0<p>In Chesapeake Bay a cold-water species of seagrass is currently hitting its heat limit, especially in summer, according to Alexander Challen Hyman of University of Florida's School of Natural Resources and Environment. As waters continue to warm due to climate change, the species likely will disappear there.</p><p>Climate-driven sea-level rise complicates the problem as well. Seagrasses thrive at specific depths — too shallow and they dry out or are eaten, too deep and there isn't enough light for photosynthesis.</p>
But There’s Good News, Too<p>Luckily, left to its own devices, a seagrass meadow can flourish for hundreds of years, according to a <a href="https://royalsocietypublishing.org/doi/10.1098/rspb.2019.1861" target="_blank" rel="noopener noreferrer">paper</a> published last year by Hyman and other researchers from the University of Florida. The researchers arrived at their conclusion by looking at shells of living mollusks and fossil shells to estimate the ages of meadows in Florida's Big Bend region on the Gulf Coast.</p><p>That area has extensive, relatively pristine seagrass meadows. "Our motivation was to understand the past history of these systems, and shells store a lot of history," said co-author Michal Kowalewski.</p><p>A high degree of similarity between living and dead shells indicates a stable area, while a mismatch suggests an area shifted from seagrass to barren sand. The researchers found that long-term accumulations of shells resembled living ones, suggesting that the seagrass habitats have been stable over time.</p><p>That stability allows biodiversity to thrive, creating conditions where specialist species can survive and flourish, according to Hyman.</p><p>Discovering the long-term stability of seagrass meadows has implications for choosing restoration sites, Kowalewski notes.</p><p>"There must be reasons they thrive in one place, while a mile away they don't and fossil data says they probably never did," he said. "If we remove a seagrass patch, we cannot hope to plant it somewhere else. It's not just the seagrass that is special. The location at which it's found is special, too."</p><p>A better approach is conserving these habitats in the first place, but we're not doing enough of that right now. The UN reports that marine protected areas safeguard just 26% of recorded seagrass meadows, compared with 40% of coral reefs and 43% of mangroves.</p>
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