United States: As health authorities pivot increasingly toward analyzing sewage as a method for monitoring the transmission of H5N1 avian influenza among US dairy herds, certain scholars are raising doubts regarding the efficacy of these wastewater tests.
Despite assertions from the US Centers for Disease Control and Prevention affirming the standardized nature of current testing procedures, some researchers harbor reservations.
“At present, we are employing rather broad diagnostic measures to scrutinize influenza A viruses in sewage,” remarked epidemiologist Denis Nash, alluding to a category encompassing typical human influenza strains as well as the avian flu present in dairy cows, wild avifauna, and domestic fowl, as reported by Los Angeles Times.
“There exists a possibility that in certain locales across the nation, the primers utilized in these assays…may prove inadequate for H5N1 detection,” stated Nash, esteemed professor of epidemiology and executive overseer of City University of New York’s Institute for Implementation Science in Population Health.
This predicament arises from the fact that the prevailing testing methodologies—namely, polymerase chain reaction (PCR) assays—are engineered to detect genetic material from a specific organism, such as a strain of influenza virus.
However, for successful identification, these tests necessitate specific priming to target the desired viral components. Depending on the viral segment under scrutiny, the presence of the H5N1 avian flu subtype may elude detection.
Human influenza A comprises two prevalent strains: H1N1 and H3N2. The designation “H” denotes hemagglutinin, a discernible protein within the viral structure, while “N” signifies neuraminidase, as per LA Times.
Conversely, avian influenza A, though of the same viral category, exhibits the H5N1 subtype.
Consequently, despite sharing the N1 signal, human and avian influenza viruses diverge in their H subtype.
Should a test primarily target H1 and H3 markers indicative of influenza A, it would overlook the avian flu strain.
Marc Johnson, a professor specializing in molecular microbiology and immunology at the University of Missouri, expressed skepticism regarding this scenario. He posited that the generic testing panels widely employed would encompass markers for H1, H3, and H5.
While acknowledging his laboratory’s specific focus on H1 and H3 detection, Johnson remarked, “I surmise our approach may be an exception,” as per the LA Times
Only in recent years have health authorities begun utilizing wastewater as a barometer for community health.
Alexandria Boehm, a professor of civil and environmental engineering at Stanford University and lead investigator for WastewaterSCAN, recounted the burgeoning prominence of wastewater surveillance, particularly amidst the pandemic. It has emerged as a routine method for detecting myriad viruses and pathogens within municipal sewage.
“Merely three or four years ago, such practices were unheard of,” Boehm reflected, underscoring the evolutionary trajectory of wastewater surveillance.
Since the initial report of avian influenza in Texas dairy cattle in late March, researchers and public health officials have been scrutinizing wastewater samples. The majority employ existing influenza A assays tailored for human strains rather than those specific to avian flu.
The CDC recently unveiled a dashboard delineating wastewater sites where influenza A has been detected in the preceding fortnight. Spanning a network of over 650 sites nationwide, only three exhibited influenza A levels warranting further investigation, while data from over 400 sites were inconclusive.
Jonathan Yoder, deputy director of the CDC’s Division of Infectious Disease Readiness and Innovation, attributed the inconclusive data to insufficient testing duration or inadequate influenza A samples.
Responding to queries regarding the potential shortcomings of current testing methodologies, Yoder affirmed, “We possess no evidence to suggest such inadequacies. Our surveillance appears sufficiently comprehensive to detect H5,” as per LA Times.
He asserted the uniformity of testing protocols across the network, emphasizing adherence to CDC-published clinical assays for influenza A.
However, disparities persist between the CDC’s findings and those of other entities.
Earlier this week, a consortium comprising scientists from Baylor College of Medicine, the University of Texas Health Science Center at Houston, the Texas Epidemic Public Health Institute, and the El Paso Water Utility published a report indicating elevated levels of avian influenza in wastewater across nine Texan municipalities. Their findings indicate that H5N1 is the predominant influenza A strain present.
Unlike other research groups, including the CDC, they employed an “agnostic” approach known as hybrid-capture sequencing.
Eric Boerwinkle, dean of the UTHealth Houston School of Public Health, elucidated this approach, distinguishing it from conventional PCR testing. “Rather than targeting a single virus or subset, we analyze the complex viral milieu present in wastewater,” he explained.
Boerwinkle and his colleagues underscored their ability to specifically identify H5N1 within wastewater samples, albeit without pinpointing its source.
Texas, situated at the intersection of multiple migratory bird flyways, represents a likely origin for avian influenza, owing to its agricultural landscape and abundant avifauna.
However, they expressed confidence in ruling out human-to-human transmission based on genomic analyses, which detected hallmark genetic disparities between human and bovine H5N1 strains.
Devabhaktuni Srikrishna, CEO of PatientKnowHow.com, commended the Texas consortium’s approach as a breakthrough in metagenomic testing for wastewater and air samples.
He hailed it as a “proof of concept” for swiftly and cost-effectively screening thousands of microorganisms, including pathogens.
“They’ve demonstrated its feasibility,” Srikrishna remarked, highlighting the collaborative efforts of government agencies, private enterprises, and academic institutions in advancing this nascent field.