Bugging The System

A blog about microbes, diseases and biomedical research advances. Posts in English or German.

1. The Bicycle Trip

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A cycling trip with consequences: Which disease did the patient pick up in Central Europe? Image by Michaela Maya, available on flickr (CC BY-NC-ND 2.0)

June 28th 2014.
A 21-year-old female is admitted to the emergency department of the Hôpital Croix-Rousse in Lyon, France. The patient is running a high fever (40.6°C) and she is hallucinating. She is with her mother, who tells the doctors the following: Her daughter had fallen sick with flu 10 days before. She had made sure that her daughter got bedrest in their home and gave her some aspirin for the headaches she had been complaining about. After about a week, the symptoms had improved and her fever had fallen. But the day before, the fever had returned and soon reached 39°C. The headaches were back too. Even worse than before, the girl had told her. She also started feeling a stinging pain in her neck. She said the pain made her dizzy and nauseous, and she felt sick twice. The fever then rose even further and the girl started hallucinating and slipping in and out of consciousness. At this point, the mother called an ambulance to bring her to the hospital. The doctors ask the mother whether her daughter had previously suffered from serious diseases or if she had taken other medicines than pain killers, which the mother dismisses. When asked for a travel history, the woman tells the doctors that the girl had returned from a Budapest-Vienna cycling trip along the Danube River about three weeks earlier. She had made the trip with three friends, which were all healthy to the knowledge of the mother.

So, what is making the patient sick?

The key to solving this case is the timing and the location of the cycle trip the girl made. She biked through parts of Hungary, Slovakia and Austria in late May. As neither her mother nor any of the friends that went on the trip got sick, it is likely whatever she had picked up was not easily transmitted from person to person. If she had been infected during the trip, the disease would have an incubation time of around two weeks and then plague her with headaches, fever, fatigue and pain. It would get better intermittently and then hit even harder after. Can you guess it already?

The answer is….

tick-borne_encephalitis_virus_crop

Electron micrograph of tick-borne encephalitis virus. Image via Wikimedia Commons (CC BY-SA 3.0)

Tick-borne encephalitis (often shortened to TBE).

An infected tick bit the girl and passed the disease on to her. Ticks feel at home in tall grass and undergrowth, and they are particularly active in spring and early summer. These parasites suck blood for food. When they grab hold of a passing animal – or as in this case a human – they search for the perfect feeding spot and bite. The bite of these critters is usually painless for the victim, thanks to natural painkillers in the tick’s saliva. Ticks can feed for several days until they are literally soaked in blood: they can suck up to 250 times their initial body weight. After the blood meal, they let go of their victim and disappear.

People do not always realise they have been bitten, and many do not know of the dangers that a tick bite can pose in Eastern and Central Europe. Ticks here sometimes spread more than the well-known tick-borne Lyme disease: in some areas, large populations carry the TBE virus which causes encephalitis – a serious infection of the brain.

tick_before_and_after_feeding

A tick before and after feeding. The animals can increase their body weight up to 250 times during a bloodmeal. Image via Wikimedia Commons (CC BY-SA 3.0).

When bitten by a tick infected with the TBE virus, many people do not fall ill. Around two out of three cases are asymptomatic – the person infected does not show signs of the disease. In the remaining cases, most people only suffer from flu-like symptoms – just like in the initial phase of the described case. Some people, however, then develop more severe symptoms and have to be admitted to hospital.  Symptoms in the second phase arise once the virus infects regions of the brain; once there, it may cause high fever, hallucinations, seizures, speaking difficulties and paralysis. In many cases, these symptoms eventually disappear as the infection ceases, but long-term damage of the brain is possible. Around one in one hundred people that falls sick with TBE dies from the infection.

TBE cannot effectively be treated once it has developed. Treatment focuses on the relief of symptoms, such as dampening the pain with pain killers.

To limit the number of people contracting the disease, prevention is key. Avoiding ticks and their habitats, use of tick-deterring insect repellents and checking for ticks after each trip to high grass are some possibilities to limit exposure, vaccination is another. The TBE vaccine is recommended in some of the core TBE areas, including the highly affected Austria. Here, in some areas up to 5% of the tick population carries the virus. Despite Austria’s classification as a high-risk TBE country, only less than one hundred Austrians develop TBE each year. This is largely thanks to the population’s relatively high vaccination rate of 85%.

 

The case described in this post is entirely fictional, but the disease course described is in line with symptoms commonly seen with TBE.

More information on TBE and TBE vaccinations can be found here:
http://www.nhs.uk/Conditions/Tick-borne-encephalitis/Pages/Introduction.aspx
http://www.cdc.gov/vhf/tbe/

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This entry was posted on October 17, 2016 by in Medical Mysteries and tagged , , , , , , , .

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