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Ticks Spread Plenty More for You to Worry About Beyond Lyme Disease



There is a short window between when a tick bites and when it comes to bacteria or virus. MSU Ag Communications, Courtesy Dr. Tina Nations, CC BY-ND

When it comes to problems caused by ticks, Lyme disease hogs a lot of the limelight.

In fact, the number of tick-borne disease cases is on the rise in the United States. The range of 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.

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.

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 the bacteria when they drink animals' blood.

Probably the most well-known of these bacterial diseases is Rocky Mountain spotted fever, the most frequently reported rickettsial disease in the world the US, with about 6,000 cases each year.

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 headaches, 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, and death can occur in severe cases. Untreated, the mortality rate is about 20%; and even with treatment, 4% of those infected the.

Not all 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. Rickettsia bacteria on a bed with a needle in a haystack. The primary carriers are the American dog tick in the eastern US. and rocky mountain wood tick in the west. The brown dog tick has just been shown to be a vector.

In most tick-borne diseases, the tick needs to be fed for some amount of time before any pathogens are transmitted. Rocky Mountain spotted fever generally take between one and three hours to arrive, so it needs to be removed quickly. Doctors usually prescribe the antibiotic doxycycline to treat Rocky Mountain spotted fever, which works quite well.

Ehrlichiosis is another bacterial disease transmitted from ticks to people. In the U.S. Ehrlichia chaffeensis bacteria, carried by lone star ticks which are common in the eastern Ehrlichia bacteria infect a type of blood cell called leukocytes. Human monocytic ehrlichiosis occurs mostly in the southern and south-central U.S.S.

Ehrlichiosis patients usually have fever, headache, muscle and progressive low blood cell count. As opposed to Rocky Mountain spotted fever, people only get 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. 5,762 cases of human granulocytic anaplasmosis reported to the CDC in 2017.

A female Ixodes scapularis tick.
Dr. Blake Layton, MSU CC BY-ND

Symptoms include fever, headache, muscle and progressive low white blood cell count. It's the deer tick Ixodes scapularis – famously so responsible for Lyme disease – that transmits the Anaplasma bacteria to humans. There's the unlucky chance that it could tick you out. Again, recommended therapy is doxycycline.

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 similar to dengue fever. The main dengue-like viral disease is 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 resembles 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..

Powassan is a rare but serious human disease, characterized by a sudden onset of fever with temperatures 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 Powass have been reported in North America, with about half of them being fatal. Its incidence seems to be increasing; there were 34 cases of Powassan reported during 2017. Ixodes cookei – infect animals with the virus via their bites. Tiny larval lone star ticks next to a penny.
Jerome Goddard

In the last decade, researchers have found additional new tick-borne viruses in the US About 30 cases of Heartland virus have thus far been identified.

A few cases of a new Thogotovirus called Bourbon virus have been identified in the Midwest and Southern US.

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 the alpha-gal molecule that's found in animal blood and other tissues.

Then days or weeks later, he or she may develop hives, 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.

Overall, people should be aware of what tick-borne diseases are present in their area and use personal protection techniques when outdoors in tick-infested areas. Remember that ticks often come into 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.

[ You're smart and curious about the world. So are The Conversation's authors and editors. You can read us daily by subscribing to our newsletter. ]  The Conversation

Jerome Goddard, Extension Professor of Biochemistry, Molecular Biology, Entomology and Plant Pathology, Mississippi State University

This article is from The Conversation under a Creative Commons license. Read the original article.

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