Outbreak News Today

From Lyme to Powassan: Tick-borne diseases in the US 2016

Tick-borne infections are a major infectious disease problem in the United States as we see the numbers increase each year and a geographical spread reported.

Ticks are arachnids, like spiders, scorpions and mites,  from the Class Arachnida. While most tick bites do not transmit infectious disease, some very serious infections can be contracted from the bite of this vector.

With its abdomen engorged with a host blood meal, this image depicts a lateral, or side view of a female blacklegged, or deer tick, Ixodes scapularis/CDC

Looking at Centers for Disease Control and Prevention (CDC) 2016 data, I outline the top 7 tickborne illnesses in the country, based on 2016 case tallies.

7. Powassan virus

Powassan virus (POWV)is transmitted by Ixodes tick species found in North America. It is primarily seen in the northeastern part of the United States. New York, Minnesota and Wisconsin have seen the highest number of cases.

In 2016, 22 cases of POWV were reported (21 neuroinvasive and 1 Non-neuroinvasive).

Signs and symptoms of Powassan infection can include fever, headache, vomiting, weakness, confusion, seizures, and memory loss. Long-term neurologic problems may occur. Long-term sequelae occurs in approximately 50% of patients. Approximately 10-15% of cases are fatal.

6. Tularemia

Also known as rabbit fever and deer fly fever,tularemia is caused by the bacterium Francisella tularensis. This bacterium is found in nature in rabbits, rodents, beavers, squirrels and several domestic and farm animals.

People commonly get infected from the bites of infected ticks (wood, dog) and deer flies. Hunters are at risk of infection following skinning, dressing and eating infected animals.

Drinking contaminated water has been implicated in tularemia infection. People also contract it through inhaling dust and hay that have rodent feces and carcasses.

During the last decade (2001-2010), their were a total of 1,208 human tularemia cases reported to the Centers for Disease Control and Prevention (an average of 120/year).

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In 2016, CDC reported 230 cases, although it doesn’t breakdown how many cases were tick-borne or how it was contracted.

5. Erlichia

According to the CDC, Ehrlichiosis is the general name used to describe several bacterial diseases that affect animals and humans. Human ehrlichiosisis a disease caused by at least three different ehrlichial species in the United States: Ehrlichia chaffeensisEhrlichia ewingii, and a third Ehrlichia species provisionally called Ehrlichia muris-like (EML).

Ehrlichiae are transmitted to humans by the bite of an infected tick. The lone star tick (Amblyomma americanum) is the primary vector of both Ehrlichia chaffeensis and Ehrlichia ewingii in the United States.

In 2016, 1,377 Ehrlichia chaffeensis cases were reported while 22 Ehrlichia ewingii were seen. An additional 200 cases were classified as undetermined.

Typical symptoms include: fever, headache, fatigue, and muscle aches. Usually, these symptoms occur within 1-2 weeks following a tick bite. Ehrlichiosis is diagnosed based on symptoms, clinical presentation, and later confirmed with specialized laboratory tests. The first line treatment for adults and children of all ages is doxycycline.

4. Babesia

Babesiosis is a parasitic disease of the red blood cells which can be found worldwide: however, most documented cases have been found in the United States. Most human infections are attributed to the species, Babesia microti, while other species are less often seen in zoonotic infections.

CDC reported 1,910 cases (1,585 confirmed and 325 probable).

It is seen most frequently in the Northeast (Connecticut, Massachusetts, New Jersey, New York and Rhode Island) and to a lesser extent in the upper Midwest (Minnesota and Wisconsin).

The parasite is typically transmitted through a tick bite, Ixodes scapularis in the U.S., from late spring to early fall. It can also be transmitted through blood transfusions and this is not restricted by geographical regions.

3. Anaplasma

The organism that causes this disease is called Anaplasma phagocytophilum. It is an intracellular pathogen that is part of the Rickettsia (the same group of bacteria that cause Rocky Mountain spotted fever amongst other diseases) family.

Formerly known as human granulocytic ehrlichiosis, and as the former name of the disease implies, it’s an infection of the white blood cells.

People get this infection through the bite of an infected tick. Depending on the part of the United States you are, the tick species is different: the eastern part of the country is the black-legged tick, Ixodes scapularis, and in the western part of the country, Ixodes pacificus, is usually involved. These are deer ticks that are also involved in the transmission of Lyme disease.

In 2016, 4,151 anaplasmosis cases were recorded by the CDC.

Ticks: An interview with Dan Wolff

2. Rocky Mountain Spotted Fever 

4,269 cases of Rocky Mountain Spotted Fever (RMSF) were reported in the US in 2016 (115 confirmed and 4115 probable).rlichi

RMSF is a tick borne disease caused by the organism, Rickettsia rickettsii. Typically, the progress of the disease is a sudden onset of high fever, deep muscle pain, severe headache and chills. A rash usually appears on the extremities within 5 days then soon spreads to palms and soles and then rapidly to the trunk.

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Fatalities can be seen in greater than 20% of untreated cases. Death is uncommon with prompt recognition and treatment. Still approximately 3-5% of cases seen in the U.S. are fatal.

This infection is seen in the U.S. primarily April through September, mostly in the southeast and south central. In recent years, the most cases have been seen in Oklahoma and North Carolina. Few cases are actually seen in the Rocky Mountain region.

1. Lyme disease

Lyme disease is not only the most common tick-borne disease in the US, it is the most common vector-borne disease in the country.

Each year, more than 30,000 cases of Lyme disease are reported to CDC, making it the most commonly reported tick-borne illness in the United States. The new estimate suggests that the total number of people diagnosed with Lyme disease is roughly 10 times higher than the yearly reported number.

In 2013, CDC released preliminary estimates indicating that the number of Americans diagnosed with Lyme disease each year is in excess of 300,000.

In 2016, CDC reported 36,429 cases (26,203 confirmed and 10,226 probable).

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