REVIEW Congenital Tick Borne Diseases: Is This An Alternative Route of Transmission of Tick-Borne Pathogens In Mammals? Krzysztof P. Jasik, 1 Hubert Okla, 1,2 Jan Slodki, 1 Beata Rozwadowska, 1,3 Aleksandra Slodki, 1 and Weronika Rupik 4 Abstract Tick-borne diseases (TBDs) have become a popular topic in many medical journals. Besides the obvious participation of ticks in the transmission of pathogens that cause TBD, little is written about alternative methods of their spread. An important role is played in this process by mammals, which serve as reservoirs. Trans- placental transfer also plays important role in the spread of some TBD etiological agents. Reservoir species take part in the spread of pathogens, a phenomenon that has extreme importance in synanthropic environments. Animals that accompany humans and animals migrating from wild lands to urban areas increase the probability of pathogen infections by ticks This article provides an overview of TBDs, such as tick-borne encephalitis virus (TBEV), and TBDs caused by spirochetes, a-proteobacteria, c-proteobacteria, and Apicomplexa, with particular attention to reports about their potential to cross the maternal placenta. For each disease, the method of propagation, symptoms of acute and chronic phase, and complications of their course in adults, children, and animals are described in detail. Additional information about transplacental transfer of these pathogens, effects of congenital diseases caused by them, and the possible effects of maternal infection to the fetus are also discussed. The problem of vertical transmission of pathogens presents a new challenge for medicine. Transfer of pathogens through the placenta may lead not only to propagation of diseases in the population, but also constitute a direct threat to health and fetal development. For this reason, the problem of vertical transmission requires more attention and an estimation of the impact of placental transfer for each of listed pathogens. Key Words: Tick-borne diseases—Congenital diseases—Transplacental transmission. Introduction D uring the last 30 years, much attention has been paid to diseases transmitted by ticks—tick-borne dis- eases (TBDs). There is an extensive literature describing this issue, usually epidemiologically, and drawing attention to the methods of how the various pathogens are spread. Ticks function as vectors, but animals that are their reser- voirs play an important role as well. Many publications describe the phenomenon of pathogen transfer between vectors—ticks—which can be done by co-feeding and vertically by germ cells. Relatively few publications describe cases of pregnant mother and newborn infections, pointing out another possi- bility of TBD pathogens spread by penetration through the placenta of infected animals and humans, in other words, the possibility of intergenerational infection. A properly devel- oped placenta is supposed to be a selective barrier through which, theoretically, no pathogens should cross. However, this is not true. Clinical observations have provided infor- mation about etiological factors of congenital diseases that cross the placental barrier, thus confirming the transplacental transmission of such pathogens as viruses, bacteria, and protozoa (Robbins and Bakardjiev 2012). 1 Department of Skin Structural Studies, Medical University of Silesia in Katowice, School of Pharmacy with Division of Laboratory Medicine in Sosnowiec, Sosnowiec, Poland. 2 University of Silesia in Katowice, Faculty of Computer Science and Material Science, Institute of Material Science, Katowice, Poland. 3 Provincial Sanitary and Epidemiological Station in Katowice, Katowice, Poland. 4 Department of Animal Histology and Embryology, University of Silesia in Katowice, Faculty of Biology and Environmental Protection, Katowice, Poland. VECTOR-BORNE AND ZOONOTIC DISEASES Volume 15, Number 11, 2015 ª Mary Ann Liebert, Inc. DOI: 10.1089/vbz.2015.1815 637