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Notes from our lab

Larval Ticks and Lyme Disease

This photo shows the larval stage of the black-legged tick (Ixodes scapularis), about 1/25 inch long.  A larva has 6 legs, instead of the 8 we see on the nymph and adult stages, but the mouth parts are similar.  A larva must complete a blood meal before it can molt into the nymph stage.  A larva is not able to give Lyme disease to the animal it feeds on.  But it can pick up Lyme bacteria if that host animal is infected with them and then transmit them to the animal it feeds on as a nymph, and again if it survives to become a feeding adult.  Much of the Lyme disease afflicting the human population depends on larvae feeding on infected hosts, even though larvae don't give it to people directly.  The rest of the human Lyme infections come from bites by adult ticks that did not get infected as larvae, but then fed on infected animals as nymphs and molted into adults.

Infected Larvae

Some other serious tick-borne illnesses can already be in a larva before it begins its blood meal.  These pathogens can pass directly from an infected mother tick into the fertilized eggs that she lays.  When the eggs develop into larvae, those viruses or bacteria are able to be transmitted to the hosts when the larvae feed on them.  These other pathogens remain in the tick as long as it lives, and can infect the animals it later feeds on if it survives to be a nymph or adult.  Even though larvae are not vectors of Lyme disease, a bite by a larva poses some health risks for people because of these less common diseases that can be in the tick eggs.

The larva in these photographs developed in our lab from eggs laid by an engorged female tick that had been captured.

The tick shown on the left (purple background) is an Ixodes scapularis larva.  This is hard to tell with the naked eye, but under a microscope you can see that near the bottom end of the tick are structures called setae, which resemble short fine hairs.

The tick to the right (white background) is a Dermacentor variabilis larva.   D. variabilis larvae do not have setae along their bottom end, although they may have them in other areas.  And unlike I. scapularis, D. variabilis have festoons, structures that look like grooves or ridges in the bottom end.  Again, while difficult to see with the naked eye, the festoons are fairly distinctive when viewed with a magnifying glass or microscope.   

Photos by D. Schimpf
Text by D. Schimpf and C. Fisher

Microbe of the Week is written by undergraduate researcher Maria Bergquist

 

Microbe of the Week: Tick-Borne Encephalitis

Welcome to microbe of the week, where we break down the different disease-causing microbes that lurk inside our tick vectors!  This week’s microbe is 

Tick-Borne Encephalitis virus, which causes Tick-Borne Encephalitis (TBE).

What is the TBE virus?

Tick-borne encephalitis is a viral infection that specifically targets the central nervous system. TBE virus is from the genus flavivirus, the same genus that houses diseases like West Nile virus and Zika virus. This virus is primarily found along the southern border of Russia into eastern Europe but has also been found throughout other parts of Europe and Asia. A similar virus under the same genus, Powassan virus, has been reported in the United States.

The current known reservoir host for TBE virus is primarily small rodents like voles and mice. TBE virus is transmitted to humans and other animals by Ixodes ricinus in Europe and Ixodes persulcatus in Russia. TBE virus may also be contracted by consuming unpasteurized dairy products from infected animals.

Symptoms

The CDC reports symptoms of TBE as fever, achiness, loss of appetite, headache, nausea, and vomiting. They note that swelling of the brain and/or spinal cord, confusion, and sensory disturbances occur in 20-30% of cases. Symptoms occur on average after seven days but have been reported taking up to 28 days post tick bite.

Treatment

There is no known cure for TBE or Powassan Virus Disease. Medical intervention primarily involves symptom management, which is required in cases of encephalitis. Vaccines for TBE are available in some endemic areas.

A Condensed History

• 1936 — TBE described as epidemic encephalitis along the border of Russia and Japan. 
• 1937 — First isolation of TBE virus lead by Russian Virologist Lev Zilber. 
• 1941 — First vaccine for TBE developed. 
• 1970 — First case of Powassan virus discovered in the US. 
• 2019 — Reported cases of TBE range from 5,000 to 13,000 per year.

Sad news

Unfortunately our tick larvae appear to have died.

Sad day for the tick nursery....

Microbe of the Week: Crimean-Congo hemorrhagic fever virus (CCHFV)

Microbe of the Week is written by undergraduate researcher Maria Bergquist

Microbe of the Week: Crimean-Congo hemorrhagic fever virus (CCHFV)

 

Welcome to microbe of the week, where we break down the different disease-causing microbes that lurk inside our tick vectors! While our Microbe of the Week normally focuses on microbes in the United States, this week’s microbe is Crimean-Congo hemorrhagic fever virus (CCHFV)* found throughout Africa as well as spanning from Eastern Europe through the Middle East and into Western China.

*CCHFV describes the virus while CCHF describes the disease caused by the virus.

What is CCHFV?

Crimean-Congo hemorrhagic fever virus is a strain of Nairovirus and is the most widespread tick-borne virus in humans. CCHFV resides in domesticated farm animals such as cattle, sheep, and goats. It is transmitted to humans primarily by the Hyalomma species of ticks, though other Ixodid ticks are capable of spreading the virus. Ticks can remain infected with CCHFV for long periods of time and can even pass the virus on to their eggs. CCHFV can also be spread through the slaughtering of infected animals or person to person through infected bodily fluids.

Symptoms

According to the CDC, initial symptoms of CCHFV include headache, high fever, back pain, joint pain, stomach pain, vomiting, red eyes, a flushed face, a red throat, and petechiae (red spots) on the palate. After about the fourth day of symptoms, large areas of severe bruising, severe nosebleeds, and uncontrolled bleeding at injection sites may occur. Recovery takes about two weeks in most cases. The CDC reports mortality rates for CCHFV range from 9% to as high as 50%, but other academic articles average the rate at around 30%.

Treatments

While there is no known cure for CCHFV, there are supportive treatments available. According to the CDC and the WHO, it’s important to maintain fluid and electrolyte balance in patients with CCHF. Also, the antiviral drug Ribavirin has had some success in reducing viral replication in patients, though more research is required on actual effectiveness.

A Condensed History

• 12th Century — Severe hemorrhagic illness from ticks described in Tadjikistan. 
• 1944 — Russian research team lead by Mikhail Chumakov discovers hemorrhagic fever infecting Russian soldiers and Crimean farm workers. 
• 1956 — Hemorrhagic fever isolated by physician Ghislaine Courtois in the region now known as the Democratic Republic of the Congo. 
• 1967 — Techniques advance to cultivate virus in lab, increasing ability to research CCHFV. 
• 1969 — Researchers determine Crimean hemorrhagic fever and DRC hemorrhagic fever are caused by the same virus, coining the name Crimean-Congo Hemorrhagic Fever. 
• 1984 — First recorded case of using Ribavirin to treat CCHF during outbreak in South Africa. 
• February 5, 2020 — Most recent outbreak of CCHF occurs in Mali.
  

Microbe of the Week: On vacation

Hello Microbe of the Week readers.  Maria Bergquist is unavailable this week, but will return.  Please check back!

Until then, try using Medline Plus to read about Lyme disease.  Click on the link below and type Lyme disease in the search bar, Medline Plus has over 300 articles on Lyme!

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