Zika dynamics in South America: The infection dynamics of Zika virus (ZIKV) are difficult to characterize. Many ZIKV infections are asymptomatic, and the clinical presentation of ZIKV is nonspecific. Rodriguez-Barraqueret al.took advantage of a long-term health study under way in Salvador, Brazil, the epicenter of the recent outbreak in the Americas. They used multiple serological assays, from before and after the emergence of ZIKV in October 2015, to distinguish ZIKV immune responses from those against Dengue virus (DENV). About 73% of the population was attacked by ZIKV. The presence of preexisting antibodies to DENV was associated with less risk of ZIKV infection and fewer symptoms.Science, this issue p.607

We address some critical but unknown parameters of individuals and populations of Norway rats (Rattus norvegicus) that influence leptospiral infection, maintenance and spirochetal loads shed in urine, which contaminates the environment ultimately leading to human infection. Our study, conducted in Salvador, Brazil, established the average load of leptospires in positive kidneys to be 5.9 x 10⁶ per mL (range 3.1-8.2 x10⁶) genome equivalents (GEq), similar to the 6.1 x 10⁶ per ml (range 2.2-9.4 x10⁶) average obtained from paired urines, with a significant positive correlation (R²=0.78) between the two. Based on bivariate and multivariate modeling, we found with both kidney and urine samples that leptospiral loads increased with the age of rats (based on the index of body length to mass), MAT titer and the presence of wounding/scars, and varied with site of capture. Some associations were modified by sex but trends were apparent. Combining with data on the demographic properties and prevalence of leptospiral carriage in rat populations in Salvador, we estimated that daily leptospiral loads shed in the urine of a population of 82 individuals exceeded 9.1 x 10¹⁰ leptospires. These factors directly influence the risk of leptospiral acquisition among humans and provide essential epidemiological information linking properties of rat populations with risk of human infection. Leptospirosis is a human disease caused by the bacterium Leptospira. It is often acquired through contact with water/soil contaminated with leptospires shed in the urine of rats, the most important reservoirs in urban environment. We evaluated how location, sex, age and other rat characteristics can influence the amount of leptospires shed into the environment. We found that rats from different locations were able to shed different concentrations of leptospires. Rat populations were able to shed more than one billion leptospires per day. The findings of this study provide information linking rat population and the risk of human leptospirosis.

Residents of urban slums suffer from a high burden of zoonotic diseases due to individual, socioeconomic, and environmental factors. We conducted a cross-sectional sero-survey in four urban slums in Salvador, Brazil, to characterize how poverty and sanitation contribute to the transmission of rat-borne leptospirosis. Sero-prevalence in the 1,318 participants ranged between 10.0 and 13.3%. We found that contact with environmental sources of contamination, rather than presence of rat reservoirs, is what leads to higher risk for residents living in areas with inadequate sanitation. Further, poorer residents may be exposed away from the household, and ongoing governmental interventions were not associated with lower transmission risk. Residents at higher risk were aware of their vulnerability, and their efforts improved the physical environment near their household, but did not reduce their infection chances. This study highlights the importance of understanding the socioeconomic and environmental determinants of risk, which ought to guide intervention efforts.

Four spirochetes (F1^T, B21, Yale^T and AMB6-RJ) were isolated from environmental sources: F1^T and B21 from soils of an urban slum community in Salvador (Brazil), Yale^T from river water in New Haven, Connecticut (USA) and AMB6-RJ from a pond in a horse farm in Rio de Janeiro (Brazil). Isolates were helix-shaped, aerobic, highly motile and non-virulent in a hamster model of infection. Draft genomes of the strains were obtained and analysed to determine the relatedness to other species of the genus Leptospira . The analysis of 498 core genes showed that strains F1^T/B21 and Yale^T/AMB6-RJ formed two distinct phylogenetic clades within the ‘Pathogens’ group (group I). The average nucleotide identity (ANI) values of strains F1^T/B21 and Yale^T/AMB6-RJ to other previously described Leptospira species were below <84 % and <82 %, respectively, which confirmed that these isolates should be classified as representatives of two novel species. Therefore, we propose Leptospira yasudae sp. nov. and Leptospira stimsonii sp. nov. as new species in the genus Leptospira . The type strains are F1^T (=ATCC-TSD-163=KIT0259=CLEP00287) and Yale^T (=ATCC-TDS-162=KIT0258=CLEP00288), respectively.

Leptospira Infection and Disease, Brazil

SUMMARY: The house mouse (Mus musculus) and the black rat (Rattus rattus) are reservoir hosts for zoonotic pathogens, several of which cause neglected tropical diseases (NTDs). Studies of the prevalence of these NTD-causing zoonotic pathogens, in house mice and black rats from tropical residential areas are scarce. Three hundred and two house mice and 161 black rats were trapped in 2013 from two urban neighbourhoods and a rural village in Yucatan, Mexico, and subsequently tested forTrypanosoma cruzi,Hymenolepis diminutaandLeptospira interrogans. Using the polymerase chain reaction we detectedT. cruziDNA in the hearts of 4·9% (8/165) and 6·2% (7/113) of house mice and black rats, respectively. We applied the sedimentation technique to detect eggs ofH. diminutain 0·5% (1/182) and 14·2% (15/106) of house mice and black rats, respectively. Through the immunofluorescent imprint method,L. interroganswas identified in 0·9% (1/106) of rat kidney impressions. Our results suggest that the black rat could be an important reservoir forT. cruziandH. diminutain the studied sites. Further studies examining seasonal and geographical patterns could increase our knowledge on the epidemiology of these pathogens in Mexico and the risk to public health posed by rodents.