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The regional decline and rise of tick-borne encephalitis incidence do not correlate with Lyme borreliosis, Austria, 2005 to 2018.

ABSTRACT: BackgroundTick-borne encephalitis (TBE) virus is a human pathogen that is expanding its endemic zones in Europe, emerging in previously unaffected regions. In Austria, increasing incidence in alpine regions in the west has been countered by a decline in traditional endemic areas to the east of the country.AimTo shed light on the cause of this disparity, we compared the temporal changes of human TBE incidences in all federal provinces of Austria with those of Lyme borreliosis (LB), which has the same tick vector and rodent reservoir.MethodsThis comparative analysis was based on the surveillance of hospitalised TBE cases by the National Reference Center for TBE and on the analysis of hospitalised LB cases from hospital discharge records across all of Austria from 2005 to 2018.ResultsThe incidences of the two diseases and their annual fluctuations were not geographically concordant. Neither the decline in TBE in the eastern lowlands nor the increase in western alpine regions is paralleled by similar changes in the incidence of LB.ConclusionThe discrepancy between changes in incidence of TBE and LB support the contributions of virus-specific factors beyond the mere availability of tick vectors and/or human outdoor activity, which are a prerequisite for the transmission of both diseases. A better understanding of parameters controlling human pathogenicity and the maintenance of TBE virus in its natural vector-host cycle will generate further insights into the focal nature of TBE and can potentially improve forecasts of TBE risk on smaller regional scales.

SUBMITTER: Stiasny K

PROVIDER: S-EPMC8414957 | biostudies-literature |

REPOSITORIES: biostudies-literature

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Project description:Mixed or multiple-strain infections are common in vector-borne diseases and have important implications for the epidemiology of these pathogens. Previous studies have mainly focused on interactions between pathogen strains in the vertebrate host, but little is known about what happens in the arthropod vector. Borrelia afzelii and Borrelia garinii are two species of spirochete bacteria that cause Lyme borreliosis in Europe and that share a tick vector, Ixodes ricinus Each of these two tick-borne pathogens consists of multiple strains that are often differentiated using the highly polymorphic ospC gene. For each Borrelia species, we studied the frequencies and abundances of the ospC strains in a wild population of I. ricinus ticks that had been sampled from the same field site over a period of 3 years. We used quantitative PCR (qPCR) and 454 sequencing to estimate the spirochete load and the strain diversity within each tick. For B. afzelii, there was a negative relationship between the two most common ospC strains, suggesting the presence of competitive interactions in the vertebrate host and possibly the tick vector. The flat relationship between total spirochete abundance and strain richness in the nymphal tick indicates that the mean abundance per strain decreases as the number of strains in the tick increases. Strains with the highest spirochete load in the nymphal tick were the most common strains in the tick population. The spirochete abundance in the nymphal tick appears to be an important life history trait that explains why some strains are more common than others in nature. Lyme borreliosis is the most common vector-borne disease in the Northern Hemisphere and is caused by spirochete bacteria that belong to the Borrelia burgdorferi sensu lato species complex. These tick-borne pathogens are transmitted among vertebrate hosts by hard ticks of the genus Ixodes Each Borrelia species can be further subdivided into genetically distinct strains. Multiple-strain infections are common in both the vertebrate host and the tick vector and can result in competitive interactions. To date, few studies on multiple-strain vector-borne pathogens have investigated patterns of cooccurrence and abundance in the arthropod vector. We demonstrate that the abundance of a given strain in the tick vector is negatively affected by the presence of coinfecting strains. In addition, our study suggests that the spirochete abundance in the tick is an important life history trait that can explain why some strains are more common in nature than others.

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The regional decline and rise of tick-borne encephalitis incidence do not correlate with Lyme borreliosis, Austria, 2005 to 2018.

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