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Study shows increase in parasite disease in Sweden

The number of cases of disease caused by Leishmania, a parasite that is spread via bites by sand flies which are mainly found in tropical and subtropical areas and in countries around the Mediterranean, has increased in Sweden. The most serious form of the disease usually leads to death if untreated.

First published: 2019-05-06

“This disease is still very rare in Sweden but the number of cases has more than doubled in the last ten years. The different forms of symptoms of the disease can be very similar to those of other diagnosed diseases which give rise to persistent sores or bone marrow diseases. In order for the correct diagnosis to be made, it is therefore important that healthcare professionals in primary care, at skin clinics and children’s clinics all over Sweden are aware of this disease,” says Sara Karlsson Söbirk, infectious disease doctor at Helsingborg Hospital. She has examined the prevalence of the disease in Sweden over a period of 23 years and presented the results in a thesis at Lund University. This has never been done previously. In addition, she has made a discovery that could contribute to the development of a vaccine for the disease.

“In collaboration with the Public Health Agency of Sweden, we have investigated the number of cases that occurred between 1993 and 2016 and we saw a peak of 35 cases in 2016 which was probably a direct consequence of the large influx of refugees the year before, since most of the persons afflicted were from Syria and Afghanistan. It is likely that the number of cases in Sweden will increase in the future and therefore it is good if the healthcare services know which patient categories they should pay special attention to.”

The 3-mm long sand fly, which is a vector for the parasite and infects humans by biting them, is found, for example, in Asia, the Middle East, Southern and Central America, Africa and countries around the Mediterranean, but not in northern Europe.

“The people who have been diagnosed in Sweden have either immigrated to Sweden or been travelling in one of the hundreds of countries where the infectious sand flies exist.”

Most of the people who become infected with the parasite do not become ill but for some people, the disease develops soon after being bitten. For others, the infection can be latent for many years, that is to say, living parasites can remain in the body without giving rise to any symptoms. Not until the immune system is weakened does the parasite become active. Every year, at least 1 million people around the world are infected, leading to disease in the skin, mucous tissues or inner organs. The most serious form of the disease is when inner organs are attacked (visceral leishmaniasis) which is often fatal if it is not detected and treated in time.

“We found only five occurrences of the most serious form of the disease in Sweden during the 23 years that we studied. However, about 400,000 cases are diagnosed around the world every year. The most common form of the disease in Sweden (93 percent of the cases) is the skin variety, cutaneous leishmaniasis, which often heals but can give rise to ugly scars in the face and on the arms and legs.”

Sara Karlsson Söbirk says there is a great need for an effective vaccine, more effective medication and clearer treatment recommendations. In her studies, she made a discovery which could lead to increased knowledge about the way the parasite interacts with the immune system and this could contribute to the development of a vaccine and improved medication in future to treat the infections that the Leishmania parasite causes.

“We have seen that a number of chemokines, which are tiny little molecules that are produced and secreted by many cells in the body and which have been shown previously to have a lethal effect on different bacteria and fungi cells, also seem to have a lethal effect on cultivated leishmania cells.

We are going to continue to study the parasite’s interaction with the immune system in order to find new ways of attacking them via a vaccine or medication. In a national study and together with the Public Health Agency of Sweden, we are going to continue to monitor patients with the disease in Sweden, and together with Leishmania researchers in other European countries we will describe risk factors, the effects of different forms of treatment, and give recommendations about the best way of treating an infection caused by a specific species of Leishmania.”

Sara Karlsson Söbirk defended her thesis at Lund University on 5 April 2019. The title of her thesis is: Leishmaniasis in Sweden. Molecular, diagnostic and epidemiological studies of the parasite Leishmania in a non-endemic country.

https://portal.research.lu.se/portal/en/publications/leishmaniasis-in-sweden-molecular-diagnostic-and-epidemiological-studies-of-the-parasite-leishmania-in-a-nonendemic-country(e37ea4e5-7405-4be3-aa01-5ba7cf3c54da).html

Folkhälsomyndigheten (Public Health Agency of Sweden):

https://www.folkhalsomyndigheten.se/

For more information, contact:
Sara Karlsson Söbirk, mobile 0708-208605, email: sara [dot] karlsson_sobirk [at] med [dot] lu [dot] se

 

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