Legionella is one of the most important waterborne pathogens that can lead to both outbreaks and sporadic cases. The majority of travel-associated Legionnaires' disease (TALD) cases are contracted during hotel stays. The aim of this study was to evaluate the prevalence and genetic diversity of Legionella spp. in hotel water supply systems in Latvia. In total, 834 hot water samples were collected from the water systems of 80 hotels in Latvia. At least one Legionella spp. positive sample was detected in 47 out of 80 hotels (58.8%). Overall, 235 out of 834 samples (28.2%) were Legionella spp. positive. The average hot water temperature in Latvian hotels was 49.8 °C. The most predominant L. pneumophila serogroup (SG) was SG3 which was found in 113 (49.8%) positive samples from 27 hotels. For 79 sequenced L. pneumophila isolates, 21 different sequence types (ST) were obtained, including 3 new types-ST2582, ST2579, and ST2580. High Legionella contamination and high genetic diversity were found in the hotel water supply systems in Latvia, which, together with the insufficient hot water temperature, may indicate that the lack of regulation and control measures may promote the proliferation of Legionella.

Legionella is an opportunistic pathogen with a biphasic life cycle that occasionally infects humans. The aim of the study was to assess the distribution of virulence genes and genetic diversity among L. pneumophila isolated from water supply systems of residential buildings in Latvia. In total, 492 water samples from 200 residential buildings were collected. Identification of Legionella spp. was performed according to ISO 11731, and 58 isolates were subjected to whole-genome sequencing. At least one Legionella-positive sample was found in 112 out of 200 apartment buildings (56.0%). The study revealed extensive sequence-type diversity, where 58 L. pneumophila isolates fell into 36 different sequence types. A total of 420 virulence genes were identified, of which 260 genes were found in all sequenced L. pneumophila isolates. The virulence genes enhC, htpB, omp28, and mip were detected in all isolates, suggesting that adhesion, attachment, and entry into host cells are enabled for all isolates. The relative frequency of virulence genes among L. pneumophila isolates was high. The high prevalence, extensive genetic diversity, and the wide range of virulence genes indicated that the virulence potential of environmental Legionella is high, and proper risk management is of key importance to public health.

L. pneumophila counts increased by more than ten-fold in the P-reduced domestic hot water system once the heat exchanger setpoint was periodically lowered.

Background: Biofilms, when formed on the surfaces of water pipes, can be responsible for a wide range of water quality and operational problems. We sought to assess the bacterial and free-living protozoa (FLP) diversity, in relation to the presence of Legionnaire's disease-causing bacteria Legionella pneumophila ( L. pneumophila ) in 45 biofilms of hot water distribution system pipes of apartment buildings in Riga, the capital city of Latvia. Results: 16S rRNA amplicon sequencing (metataxonomics) revealed that each biofilm contained 224 rather evenly distributed bacterial genera and that most common and most abundant were two genera, completely opposites in terms of their oxygen requirements: the obligately anaerobic Thermodesulfovibrio and the strictly aerobic Phenylobacterium . Water temperature and north-south axis (i.e., different primary water sources) displayed the most significant effect on the inter-sample variations, allowing us to re-construct three sub-networks (modules) of co-occurring genera, one involving (potentially FLP-derived) Legionella spp. Pangenome-based functional profile predictions suggested that all three may be dominated by pathways related to the development and maintenance of biofilms, including quorum sensing and nutrient transport, as well as the utilization of various energy sources, such as carbon and nitrogen. In our 18S rRNA amplicon sequencing data, potential hosts of L. pneumophila were detected in 11 out of 12 biofilm samples analyzed, however, in many cases, their relative abundance was very low (<1%). By validating our findings using culture-based methods, we detected L. pneumophila (serogroups 2, 3, 6 and 9) in nine (20%) biofilms, whereas FLP (mostly Acanthamoeba, Vahlkampfidae and Vermamoeba spp.) were present in six (~13%) biofilms. In two biofilms, L. pneumophila and its potential hosts were detected simultaneously, using culture-based methods. Conclusions: Overall, our study sheds light on the community diversity of hot water biofilms and predicts how several environmental factors, such as water temperature and source might shape it.

In 2014, African swine fever (ASF) emerged in Latvia for the first time. The majority of cases appeared in wild boar, but the presence of ASF in these animals constitutes a permanent threat to domestic pig holdings. Recent studies have shown an increase in serologically positive and a decrease in PCR-positive ASF cases in wild boar, possibly indicating a decline of ASF incidence. We aimed to investigate the course of the ASF epidemic in wild boar in Latvia, thus attaining further insights into the ASF epidemiology in this country with the goal of assessing the stage of the epidemic. Latvian ASF surveillance data of wild boar were utilized to estimate the seroprevalence and ASF virus (ASFV) prevalence in the wild boar population. Prevalence estimates were obtained for both the eastern and western part of the country and in addition for the 2014/2015 to 2018/2019 hunting seasons. Moreover, prevalence estimates for three different age classes were calculated. An increase in serologically positive yet PCR-negative wild boar samples from active surveillance was identified over time. When comparing the age groups, wild boar younger than one year displayed the ASFV prevalence to be higher than the seroprevalence, whereas older animals shared higher seroprevalence estimates. These findings support the assumption that only a small proportion of affected animals survive an infection, leading to an accumulation of their numbers over time. As a result, ASF elimination in a country with an infected wild boar population could possibly be achieved, if effective wild boar population management and surveillance is maintained and combined with the detection and removal of wild boar carcasses to reduce the viral load in the environment. In addition, the wild boar population should be kept as small as possible to break the ASFV infection cycle.

Background and Objectives:Legionella is one of the most important water-related pathogens. Inside the water supply systems and the biofilms, Legionella interact with other bacteria and free-living amoeba (FLA). Several amoebas may serve as hosts for bacteria in aquatic systems. This study aimed to investigate the co-occurrence of Legionella spp. and FLA in drinking water supply systems. Materials and Methods: A total of 268 water samples were collected from apartment buildings, hotels, and public buildings. Detection of Legionella spp. was performed in accordance with ISO 11731:2017 standard. Three different polymerase chain reaction (PCR) protocols were used to identify FLA. Results: Occurrence of Legionella varied from an average of 12.5% in cold water samples with the most frequent occurrence observed in hot water, in areas receiving untreated groundwater, where 54.0% of the samples were Legionella positive. The occurrence of FLA was significantly higher. On average, 77.2% of samples contained at least one genus of FLA and, depending on the type of sample, the occurrence of FLA could reach 95%. In the samples collected during the study, Legionella was always isolated along with FLA, no samples containing Legionella in the absence of FLA were observed. Conclusions: The data obtained in our study can help to focus on the extensive distribution, close interaction, and long-term persistence of Legionella and FLA. Lack of Legionella risk management plans and control procedures may promote further spread of Legionella in water supply systems. In addition, the high incidence of Legionella-related FLA suggests that traditional monitoring methods may not be sufficient for Legionella control.

Abstract Legionella pneumophila is an environmental pathogen of engineered water systems that can cause different forms of legionellosis - from mild fever to potentially lethal pneumonia. Low concentrations of legionellae in natural habitats can increase markedly in engineered hot water systems where water temperatures are below 55 °C. In the current study, we aimed to investigate the influence of sampling season, hot water temperature and sampling protocol on occurrence of L. pneumophila. A total of 120 hot water samples from 20 apartment buildings were collected in two sampling periods - winter 2014 (n = 60) and summer 2015 (n = 60). Significantly higher occurrence of L. pneumophila was observed in summer 2015. Significant differences in temperature for negative and positive samples were not observed, which can be explained by low water temperatures at the point of water consumption. Temperature above 55 °C was observed only once, for all other sampling events it ranged from 14 °C to 53 °C.

Continuous environmental exposure of humans to Legionella may induce immune responses and generation of antibodies. The aim of this study was to investigate the seroprevalence of Legionella pneumophila serogroups (SG) 1–6 in the general healthy population and identify the associated host-related and environmental risk factors. L. pneumophila SG 1–6 seroprevalence among a total of 2007 blood samples collected from healthy donors was 4.8%. Seroprevalence was higher in women (5.9%) than men (3.3%) and in areas with a larger number of inhabitants, ranging from 3.5% in rural regions to 6.8% in the capital, Riga. Blood samples from inhabitants of apartment buildings tested positive for L. pneumophila in more cases (5.8%) compared to those from inhabitants of single-family homes (2.7%). Residents of buildings with a municipal hot water supply system were more likely to be seropositive for L. pneumophila (OR = 3.16, 95% CI 1.26–7.91). Previous episodes of fever were additionally identified as a risk factor (OR = 2.42, 95% CI 1.43–4.1). In conclusion, centralized hot water supply, female gender and previous episodes of fever were determined as the main factors associated with L. pneumophila seropositivity in our study population.