The Geographic Information System applied to study schistosomiasis in Pernambuco

Impact of environmental factors on Biomphalaria pfeifferi vector capacity leading to human infection by Schistosoma mansoni in two regions of western Côte d'Ivoire

ABSTRACT: BACKGROUND: Intestinal schistosomiasis remains a worrying health problem, particularly in western Côte d'Ivoire, despite control efforts. It is therefore necessary to understand all the factors involved in the development of the disease, including biotic and abiotic factors. The aim of this study was to examine the factors that could support the maintenance of the intermediate host and its vectorial capacity in western Côte d'Ivoire.

METHODS

Data on river physicochemical, microbiological, and climatic parameters, the presence or absence of snails with Schistosoma mansoni, and human infections were collected between January 2020 and February 2021. Spearman rank correlation tests, Mann-Whitney, analysis of variance (ANOVA), and an appropriate model selection procedure were used to analyze the data.

RESULTS

The overall prevalence of infected snails was 56.05%, with infection reaching 100% in some collection sites and localities. Of 26 sites examined, 25 contained thermophilic coliforms and 22 contained Escherichia coli. Biomphalaria pfeifferi was observed in environments with lower land surface temperature (LST) and higher relative air humidity (RAH), and B. pfeifferi infection predominated in more acidic environments. Thermal coliforms and E. coli preferred higher pH levels. Lower maximum LST (LST_Max) and higher RAH and minimum LST (LST_Min) were favorable to E. coli, and lower LST_Max favored coliforms. The presence of B. pfeifferi was positively influenced by water temperature (T °C), LST_Min, RAH, and precipitation (Pp) (P < 0.05) and negatively influenced by pH, total dissolved solids (TDS), electrical conductivity (EC), LST_Max, and mean land surface temperature (LST). The parameters pH, TDS, EC, LST_Min, LST, and Pp had a positive impact on snail infection, while LST_Max had a negative impact on infection. Only pH had a positive effect on coliform and E. coli abundance. Of the 701 people examined for human schistosomiasis, 73.13% were positive for the point-of-care circulating cathodic antigen (POC-CCA) test and 12.01% for the Kato-Katz (KK) test. A positive correlation was established between human infections and the abundance of Biomphalaria (r2 = 0.879, P = 0.04959).

CONCLUSIONS

The results obtained reflect the environmental conditions that are conducive to the maintenance of S. mansoni infection in this part of the country. To combat this infection as effectively as possible, it will be necessary not only to redouble efforts but also to prioritize control according to the level of endemicity at the village level.

Assessment of schistosomiasis transmission in the River Nile at Greater Cairo using malacological surveys and cercariometry

Continuous field studies on the abundance and distribution of freshwater snails and cercarial populations are important for schistosomiasis control programs. In the present work, snail surveys and cercariometry were conducted for four successive seasons at 12 sites on the Nile River banks in the area of Greater Cairo to identify potential transmission foci for schistosomiasis. In addition, water physicochemical parameters were recorded. The results showed that the electrical conductivity, total dissolved solids, dissolved oxygen, and pH were within the permissible levels, except that the water temperature increased, especially in the spring season. Malacological surveys identified 10 native snail species at the studied sites of the Nile River, namely Bulinus truncatus, Biomphalaria alexandrina, Lymnaea natalensis, Lanistes carinatus, Cleopatra bulimoides, Melanoides tuberculata, Helisoma duryi, Bellamya unicolor, Physa acuta, Thedoxus niloticus, and one invasive snail species, Thiara scabra. The calculated diversity index indicated that the structure of snails' habitats was poor, while Evenness index indicated that the individuals were not distributed equally. Natural infection results identified no schistosome cercariae in B. truncatus and B. alexandrina. However, the cercariometry recovered Schistosoma cercariae in all the surveyed sites during all seasons with variable distribution. The preceding data suggest that there are still some active transmission foci for schistosomiasis infection in the Nile River. Moreover, the present finding highlights the importance of cercariomety as a complementary approach to snail samplings for identifying the transmission foci for schistosomiasis.

Basic and associated causes of schistosomiasis-related mortality in Brazil: A population-based study and a 20-year time series of a disease still neglected

Background

Schistosomiasis is a persistent public health problem in Brazil. Regardless advances in diagnosis and mass treatment, schistosomiasis has a severe impact on morbimortality in the country and remains a neglected tropical disease. Herein, we assessed the basic and associated causes of schistosomiasis-related deaths and the temporal and spatial patterns of mortality from the disease in Brazil between 1999 and 2018.

Methods

We conducted an ecological and time series study. The segmented log-linear regression model was applied to assess time trends, considering all deaths recorded in the category B65/ICD-10. Additionally, we elaborated maps of mortality rates from schistosomiasis in Brazil.

Results

A total of 4168 schistosomiasis-related deaths were recorded in Brazil in this period, as an associated cause. Time trend analysis revealed an increase in the average age of deaths from schistosomiasis (annual percentage change (APC) = 0.84), and stable trend in Brazil (APC = 0.31). Concerning schistosomiasis-related deaths, we observed disorders related to the digestive system, liver diseases, septicemias, and chronic diseases. Surprisingly, there were deaths caused by non-endemic Schistosoma species in Brazil. Also, municipalities from non-endemic areas in Brazil presented schistosomiasis-related deaths.

Conclusion

Altogether, our analyses demonstrated that schistosomiasis remains a significant cause of death in Brazil, and it is increasing in some areas, especially in the Northeast region. Additionally, women and the elderly showed a stable time trend of deaths. Thereby, it urgently requires improvements in the control programs strategies, in the sense of an effective reduction in cases and deaths from the disease in Brazil.

Persistence of Schistosomiasis-Related Morbidity in Northeast Brazil: An Integrated Spatio-Temporal Analysis

Objective: To analyze the temporal trend and spatial patterns of schistosomiasis-related morbidity in Northeast Brazil, 2001–2017. Methods: Ecological study, of time series and spatial analysis, based on case notifications and hospital admission data, as provided by the Ministry of Health. Results: Of a total of 15,574,392 parasitological stool examinations, 941,961 (6.0%) were positive, mainly on the coastline of Pernambuco, Alagoas and Sergipe states. There was a reduction from 7.4% (2002) to 3.9% (2017) of positive samples and in the temporal trend of the detection rate (APC—11.6*; Confidence Interval 95%—13.9 to −9.1). There was a total of 5879 hospital admissions, with 40.4% in Pernambuco state. The hospitalization rate reduced from 0.82 (2001) to 0.02 (2017) per 100,000 inhabitants. Conclusion: Despite the reduction in case detection and hospitalizations, the persistence of focal areas of the disease in coastal areas is recognized. This reduction may indicate a possible positive impact of control on epidemiological patterns, but also operational issues related to access to healthcare and the development of surveillance and control actions in the Unified Health System.

Population-based, spatiotemporal modeling of social risk factors and mortality from schistosomiasis in Brazil between 1999 and 2018

Schistosomiasis remains a significant public health concern in Brazil. To identify areas at, and social determinants of health (SDH) associated with, high-risk for schistosomiasis-related mortality from Brazil, we conducted a spatial and spatiotemporal modeling assessing all deaths confirmed in Brazil between 1999 and 2018. We used the segmented log-linear regression model to assess temporal trends, and the local empirical Bayesian estimator, the Global and Local Moran Index for spatial analysis. A total of 12,251 schistosomiasis-related deaths were reported in this period. Within the Mortality Information System (SIM) of the Brazilian Ministry of Health, the states of Alagoas (AL), Pernambuco (PE) and Sergipe (SE) recording the highest mortality rates: 2.21, 1.92 and 0.80 deaths/100,000 inhabitants, respectively. Analyses revealed an increase in the mean age of schistosomiasis-related deaths over the time assessed (APC = 0.9; p-value<0.05). Spatial analysis identified a concentration of municipalities presenting high risk of schistosomiasis-related mortality along the coastline of PE and AL. Similarly, we identified the formation of high space-time clusters in municipalities in the states of PE, AL, SE, Bahia, and Minas Gerais. Finally, mortality rates showed a significant correlation with 96.96% of SDH indices. The data reveal additional important changes in schistosomiasis-related deaths in Brazil between 1999 and 2018, such as a slow reduction among males (unlike females that displayed no change). Regardless, our analyses indicates that schistosomiasis continues to have the greatest detrimental impact in poor regions of Brazil and suggest the need for enhancement of current control measures to accelerate progress.

Mapping the risk for transmission of urban schistosomiasis in the Brazilian Northeast

This is an analysis of the risk of schistosomiasis transmission in the city of Recife in the Northeast of Brazil based on the number of schistosomiasis cases (Schistosoma mansoni) registered for the period 2007-2017 together with data resulting from active search of breeding sites of the Biomphalaria snail intermediate host. The analyses were performed using Kernel Density Estimation (KDE), SaTScan and Map Algebra methodology using human socio-demographic data and biotic and abiotic data from the snail breeding sites. Investigating 44 breeding sites resulted in a total of 3.800 snails, 31.8% of which were positive for S. mansoni DNA. These data were considered in relation to total of 652 schistosomiasis cases. The KDE showed two high-risk and two medium-risk clusters, while three significant clusters were identified by SaTScan. Combining these data with the Map Algebra methodology showed that all high-risk neighbourhoods had breeding sites with snails positive for S. mansoni. It was concluded that schistosomiasis transmission cannot be controlled without basic sanitation and sewage management in the presence of Biomphalaria snails. The technique of Map Algebra was found to be fundamental for the analysis and demonstration of areas with a high probability of schistosomiasis transmission.