The Colorado Department of Public Health and Environment (CDPHE) today reported that another worker culling poultry a second large layer farm tested positive for H5N1 avian influenza in preliminary tests, just days after it reported another case at the first farm, raising the total number to seven.
Also, the Centers for Disease Control and Prevention (CDC) confirmed initial positive results for H5N1 in two of Colorado's recent cases, detailed genetic sequencing findings from a sample from a sick Colorado poultry culler, and reported preliminary results from a seroprevalence study in Michigan farm workers.
More cases in cullers, as CDC reports sequencing findings
In a statement today, the CDPHE said the patient who tested positive in initial state testing was providing assistance at a second large layer farm hit by the virus in Weld County. Culling operations are under way at two large layer farms, which together have about 3 million birds.
Last week, federal health officials said the culling staff is working in sweltering conditions in the poultry barns, which makes personal protective equipment (PPE) less effective and may further spread environmental contamination. They also described a slow, laborious hands-on process for culling the birds that increases worker exposure to the virus.
In a July 19 statement, the CDPHE reported an additional confirmed case from the first of the two layer farms where earlier infections were reported. On the same day, the CDC said in an update that it has confirmed H5N1 in the two most recent infections from the first farm. Similar to the earlier cases, workers had mild infections and were offered the antiviral drug oseltamivir, the CDC added.
The CDC also said it has uploaded a genetic sequence of the virus from one of the Colorado cullers to public databases. It is closely related to the B3.13 genotype found in recent poultry outbreaks and infected cattle herds. "This is the only virus that CDC has been able to fully sequence out of the cases in Colorado so far," the group said.
The virus primarily has avian genetic characteristics and doesn't have changes that increase its ability to infect or spread among humans. It has the same PB2 M631L mammalian adaptation marker seen in nearly all dairy cow sequences and in Michigan's first human case. It did not have the PB2 E627K mutation—linked in the past to adaptation in mammals—that was seen in an earlier human case from Texas.
Early data suggest asymptomatic infections unlikely
In its update, the CDC also detailed initial findings from a Michigan-led seroprevalence study, which has so far looked at blood samples collected in June from 35 people who work on Michigan farms that had H5N1 outbreaks in dairy cows. The participants were from multiple counties and had different roles, though all had worked directly with sick cows. Fewer than half said they wore masks or goggles.
Researchers tested the blood samples for antibodies to the H5N1 clade 2.3.4.4b virus, which might suggest undetected infections. As a control, they also measured antibodies against seasonal flu viruses. None of the 35 workers had antibodies to H5N1, but many had neutralization antibodies to seasonal flu, suggesting prior infection or vaccination.
The CDC said the initial findings align with earlier studies from Asia that suggested low H5N1 seroprevalence, even in workers with known exposure.
The Michigan Department of Health and Human Services is continuing the study and working with the CDC to analyze the data and will submit the findings for peer-review publication. The CDC also said it is working with the American Association of Bovine Practitioners to conduct a seroprevalence study in bovine veterinarians, which will take place in 2 months.
The number of affected dairy farms continues to rise, with five more outbreaks confirmed, raising the national total to 168 from 13 states, according to the latest update from the US Department of Agriculture Animal and Plant Health Inspection Service (APHIS). Four of the latest confirmations are from Colorado, with the fifth from Minnesota.
