Context
∙ Wastewater surveillance can be a tool to monitor the presence of pathogens of diseases like malaria, dengue etc.
Vector-borne diseases
∙ Vector-borne diseases are human illnesses caused by parasites, viruses and bacteria that are transmitted by vectors. Example: Malaria, Dengue etc.
∙ Vector-borne diseases account for more than 17% of all infectious diseases, causing more than 700 000 deaths annually. They can be caused by either parasites, bacteria or viruses.
Need of Wastewater surveillance
∙ Early warning of pandemics: It can provide early warning signs of the presence of infectious diseases, such as viruses or bacteria, in a community. This allows for a quicker response to potential outbreaks and the implementation of public health measures.
∙ Wastewater surveillance carried out by the Tata Institute for Genetics and Society (TIGS) in Bengaluru was able to detect a silent wave of the XBB.1.16 Omicron variant in the city.
∙ Non-invasive Population Screening: Wastewater surveillance is a passive method that does not rely on individuals seeking testing.
∙ Identification of Asymptomatic Carriers: Wastewater surveillance can identify individuals who are shedding infectious agents, even if they are asymptomatic.
∙ Tracking Trends and Variants: Continuous monitoring of wastewater allows for the tracking of trends in the prevalence of specific pathogens over time.
∙ Cost-Effective and Scalable: It is a cost-effective and scalable method, especially in large populations. It provides a snapshot of the health status of an entire community without the need for individual testing, making it a resource-efficient approach.
∙ Integration with Traditional Surveillance: Wastewater surveillance complemented with traditional surveillance methods, such as clinical testing and case reporting provides a more comprehensive understanding of the health landscape.
Challenges
∙ Data Interpretation: Interpreting the data from wastewater surveillance requires expertise in epidemiology, virology, and environmental science. Establishing clear guidelines for interpreting results and translating them into actionable public health measures is essential.
∙ Detection Limits and Sensitivity: The sensitivity of detection methods for pathogens in wastewater may vary, and some low concentrations may go undetected.
∙ Dilution Effects: Dilution of wastewater in sewer systems can lead to underestimation of pathogen concentrations.
∙ Pathogen Stability: The stability of pathogens in wastewater can be influenced by environmental factors, such as temperature and pH.
∙ Delay in reporting results: most wastewater samples are sent to laboratories, with analysis involving either polymerase chain reaction (PCR) or genome sequencing, for identifying new variants. These methods incur a long delay in reporting results.
∙ Also the presence of PCR inhibitors in wastewater may lead to inconsistent results.
∙ Inappropriate results: In India, besides people shedding the pathogens through stools, there are several mammals, including nonhuman primates, that serve as reservoir hosts of malaria and dengue.
∙ So it is difficult to say that all the malaria and dengue microbes detected in wastewater are excreted only by humans.
Global Practices
∙ Wastewater surveillance has been routinely used for decades for tracking the polio virus in various countries.
∙ In 2022, Bangladesh launched a wastewater surveillance programme to track and monitor the pathogens like Salmonella typhi, Vibrio cholerae, and rotavirus in the communities.
Way Ahead
∙ While selecting priority pathogens of wastewater surveillance, it is essential to consider the limitations and challenges that arise from different sanitation systems and host-parasite geography.
∙ Hence the implemented techniques must be sensitive and specific, provide comprehensive and objective data, realize results in real-time, be able to monitor multiple diseases and pollutants, even those which are typical, be scalable and cost-effective; and be easy-to-use and demand no specialist resources.
