Viral threat shows up in Texas mammals
Vaccine researcher explains what’s going on with H5N1 — and why we should worry if it crosses to feral hogs
We have good news regarding the COVID-19 pandemic. The number of new COVID hospitalizations in America (and in Texas) is declining fast and could soon reach its lowest level in almost a year, or even since the start of the pandemic. The wastewater monitoring for the city of Houston is showing similar declines and there is no new obvious COVID variant ascending. We might soon enter a low COVID spring-summer.
But now there is a new concern for Texas, namely a reported human case of avian influenza caused by the H5N1 strain and connected to the first bird flu outbreak among dairy cattle in the United States.
There are several reasons why this occurrence has gotten the attention of epidemiologists and other scientists or public health experts who prepare for future pandemics.
The first is the observation that, since 2020, global H5N1 outbreaks have been on the rise and are reported with increasing frequency in both wild birds and poultry. The second is the fact that H5N1 sometimes jumps to humans, causing severe illness. The first instance of this was reported from Hong Kong in 1997, when a 3-year-old boy died from pneumonia and severe respiratory illness caused by H5N1 influenza. Since then, as of September
2019, 861 laboratory-confirmed human cases have been reported globally, with 455 deaths.
Adding to these concerns is that birds are also transmitting H5N1 to mammals with increasing frequency. This could mean that the virus is undergoing mutations to adapt better to mammals and could ultimately spread more easily to humans, or even eventually cause human-to-human transmission. Over the last two years, avian influenza viruses have jumped to sea lions living along the Pacific Coast of South America and elephant seals. The deaths were widespread and devastating, disrupting entire ecosystems.
Now something similar might be happening right here in Texas, in the Panhandle. In this case the virus is affecting dairy cattle. At least seven Texas dairy herds are affected. The new human case of H5N1 influenza in Texas is only the second case ever reported in the U.S. and was likely contracted after exposure to the infected dairy cattle. Fortunately, the individual has only mild symptoms and is being treated with oseltamivir (Tamiflu), an approved antiviral drug for many types of influenza.
The Centers for Disease Control and Prevention just completed the genetic sequence of the virus isolated from this individual. They confirm that the virus is an H5N1 influenza strain, which is highly pathogenic in birds, and that it is closely related to the virus isolated from the dairy
cattle. Moreover, it contains a mutation that has been linked previously with virus adaptation to mammals. It’s the same mutation that has been found before in H5N1 and other avian influenza strains that jumped to people.
In all, as many as five states may now have H5N1 outbreaks in cattle — Texas, Kansas, Michigan, New Mexico and Idaho. These cows may have become infected by ingesting feed or water contaminated with the virus from birds. Cowto-cow transmission may also occur, in some cases from cattle infected in Texas and shipped to other states. Although the virus does not appear to be lethal to cattle, it can make them sick or lower milk production. Moreover, the virus can contaminate the milk, which could transmit the virus to other mammals unless the milk is pasteurized. This may also explain how H5N1 infected some cats on these dairy farms.
But here’s some good news about H5N1. So far, there is no evidence that this human case of H5N1 is spreading or that human-to-human transmission is occurring. It is highly unlikely that these outbreaks among Texas cattle will ignite an epidemic in the human population. According to the CDC, “the human health risk currently remains low.” More good news: The virus isolated from humans appears to genetically resemble the inactivated virus used by manufacturers to develop two H5N1 vaccines. If the virus were to ignite a human epidemic and there were ever a need to vaccinate human populations, those vaccines are available and could be scaled up for production.
However, this new outbreak in dairy cattle is a reminder of the potential for a major avian influenza epidemic eventually occurring in the U.S. A big unknown: Is it only a matter of time before this occurs, and if so, when? This is very hard to predict.
I sometimes compare what’s happened to sea lions in South America or cattle in Texas to what a grade 4.0 or 5.0 tremor feels like to someone who lives in San Francisco. That tremor reminds you that one day a major earthquake (like the 1906 earthquake) could strike, but it’s difficult to tell whether the big one is imminent or will occur in 10 years, 100 years, or 1,000 years. It’s the same with a major human H5N1 epidemic or pandemic.
In the meantime, there are important considerations to prepare for future influenza pandemics. My colleague Michael Osterholm, an influenza expert from the University of Minnesota, says he would be more worried if it were pigs infected with this H5N1, since they are vulnerable to both human and avian flu viruses. A co-infection with both kinds of viruses could allow these viruses to reassort in pigs and produce a new virus that could infect people. That sequence of events may explain how the influenza virus that caused the terrible 1918 pandemic is thought to have first arisen on a Kansas hog farm.
Regarding this current episode in Texas cattle, I worry about our feral hog infestation — Texas hosts almost 40% of our nation’s feral hog population — and there’s a possibility that they could serve as animal reservoirs for “the big one.”
At a minimum, the unprecedented finding of H5N1 affecting cattle requires that we remain vigilant in monitoring the animal origins of RNA viruses such as influenza and coronaviruses. That means supporting university researchers here in Texas as well as international organizations committed to conducting animal surveillance for virus pathogens.
Our livestock are also vulnerable to new viruses beyond influenza. For example, African swine fever, a deadly hemorrhagic disease of pigs caused by a DNA virus (and transmitted by ticks) could enter Texas from Africa, Asia, or Eastern Europe and the Russian Federation. Potentially it could first infect our feral hog population before amplifying and crossing over to domestic swine.
Another concern is Texas cattle fever (transmitted by ticks and caused by a Babesia parasite), which could re-enter Texas from Mexico, where it is endemic. We need to harness our Texas Medical Center institutions to work hand-in-glove with our state’s two great veterinary schools and the Texas Animal Health Commission to look out for these diseases or develop next-generation animal vaccines.
Compared to other regions of the U.S., Texas is especially vulnerable to epidemics of human and animal origin. We are highly urbanized, but we still host vast herds of livestock and somewhere between 2 million and 3 million feral hogs. Due to accelerating climate change, we are at risk for animal and human illnesses transmitted by ticks and other arthropods. We must ensure our self-sufficiency for preventing these 21st-century disease threats.
Peter Hotez is professor of pediatrics and molecular virology and microbiology at Baylor College of Medicine, where he is also codirector of the Texas Children’s Hospital Center for Vaccine Development, and dean of the National School of Tropical Medicine.