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With Silent Spread of H5N1 Avian Flu in US Cattle, Wastewater Testing Emerges as Crucial

H5N1 avian flu among US cow populations

United States: Approximately a year prior, Marc Johnson, a holder of a Doctor of Philosophy degree from the University of Missouri, devised an instrument for identifying genetic material from the H5 strain of avian influenza A virus (IAV) within urban sewage, envisioning its emergence in routine surveillance, albeit not attributable to bovines.

“The emergence of this bovine matter caught us off guard,” he conveyed to CIDRAP News. “Had this apparatus been put into national practice, indications of this would have surfaced in sewage as early as February, potentially facilitating its containment. It’s truly astounding how extensively it proliferated unbeknownst to anyone,” the expert added.

However, at that juncture, the instrument had not been activated since H5N1 had not been identified until certain cattle began exhibiting symptoms towards the end of March.

Cost-effective, instantaneous alternative

According to Johnson, wastewater surveillance commences at municipal sewage treatment facilities, which cater to the vast majority of cities with populations exceeding 10,000. In the state of Missouri, for instance, these facilities accommodate approximately 60% of the populace, according to CIDRAP News.

Operators of treatment facilities compile composite samples from the water at intervals of 15 to 30 minutes, dispatching them to laboratories for concentration and extraction of viral RNA or DNA for analysis. These economic tests ascertain the presence and strains of the virus or viral fragments.

Influenza A virus, capable of infecting both animals and humans, has been the causative agent behind all global influenza pandemics. The highly pathogenic avian influenza (HPAI) strain of H5N1 surfaced in the late 1990s, propagating extensively among wild avifauna and poultry and also affecting humans.

Pivotal concerning potentially zoonotic diseases

In late March, the H5N1 clade was identified in cattle exhibiting flu-like symptoms. It had previously been detected in wild birds, poultry, and certain wild mammals amidst widespread outbreaks in the United States and other nations commencing in 2022. In April, the United States Department of Agriculture (USDA) Animal and Plant Health Inspection Service (APHIS) divulged 239 genetic sequences linked to the bovine outbreaks.

Subsequently, viral H5N1 RNA (non-infectious virus) was identified in one-fifth of pasteurized milk samples in US supermarkets (excluding sour cream, cottage cheese, or ground beef). A singular instance of human infection (the second documented case in the US) was reported in an individual employed on a dairy farm. This individual developed conjunctivitis but exhibited no additional symptoms and has since recuperated. The prior human case involved a poultry worker in Colorado in April 2022, as per CIDRAP News. 

Last month, researchers from Emory University employed a hydrolysis probe-based reverse transcription-polymerase chain reaction (RT-PCR) to quantify H5 concentrations in sewage dating back to February 4 at three sentinel Texas treatment plants proximate to the epicenter of the H5N1 outbreak.

These plants (two in Amarillo and one in Dallas) were selected from among 15 facilities, manifesting a secondary surge in IAV in March and April, subsequent to the customary flu season. Industrial discharges containing animal excreta, including dairy byproducts, had been introduced into sewage at the Amarillo facilities.

“If activities within the dairy industry in these sewage drainage areas serve as the primary source of H5 in sewage, it suggests the possibility of additional, unidentified outbreaks among cattle providing milk to these facilities, since milk from infected animals must be diverted from the food supply,” the authors of the study expounded.

H5 was undetectable before mid-March but subsequently attained comparable concentrations to IAV M genes—an index of influenza virus transmissibility—which were among the highest ever recorded in sewage. Concurrently, visits to emergency departments related to flu in the associated public health regions of Texas were dwindling.

“These findings imply that sewage surveillance is a viable approach to monitoring certain animal pathogens, furnishing an early detection mechanism particularly crucial for diseases with zoonotic potential such as HPAI,” the study’s authors concluded.

Michael Osterholm, holding a Doctor of Philosophy degree and a Master of Public Health, serving as the director of the Center for Infectious Disease Research and Policy (CIDRAP) at the University of Minnesota, the publisher of CIDRAP News, articulated that examining sewage systems devoid of animal-derived effluents could function as sentinels for human diseases.

“There exist systems devoid of animal contributions, so any surge in such systems could signify evidence of human transmission,” he remarked. He appended that certain systems of this nature might presently be conducting such tests, though he has not yet perused the data.

Monitoring mutations over time

Richard Webby, a Doctor of Philosophy and the director of the World Health Organization Collaborating Centre for Studies on the Ecology of Influenza in Animals and Birds, as well as a researcher at St. Jude’s Children’s Research Hospital in Nashville, Tennessee, contended that surveillance of both sewage and supermarket milk samples holds significance. “It provides us with an indication of whether the virus is evolving without necessitating entry into the contaminated farm environment,” he remarked.

Surveillance at sewage treatment plants servicing meat-processing facilities could also prove beneficial, according to Johnson. “We’ve witnessed this phenomenon previously, wherein viruses from slaughtered animals manifest in municipal sewage,” he remarked, noting the potential for spillover to swine or other animals. “The advantageous aspect of this is, while rather distasteful, the virus’s presence in any compartment will invariably lead to its presence in sewage,” as highlighted by CIDRAP News. 

Unlike enteric viruses, most respiratory viruses such as SARS-CoV-2, the causative agent of COVID-19, lose infectivity upon traversing the gastrointestinal tract due to their sensitivity to changes in acidity levels, Johnson elucidated, conceding his inability to culture infectious SARS-CoV-2 viruses from sewage.

This principle appears applicable to H5N1, also a respiratory virus.

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