A new pandemic

Blood is categorized into four main types—A, B, AB, or O—based on the types of antigens present on the surface of red blood cells. Antigens are proteins found on red blood cells that trigger an immune response when encountering unfamiliar substances, such as certain bacteria, Dr. Douglas Eric Guggenheim, a physician at the Abramson Cancer Center at the University of Pennsylvania Hospital, explained in a 2020 Penn Medicine article.

Increased Risk of Viral Infections

A 2023 study from Harvard Medical School, published in the journal Blood, found that the SARS-CoV-2 virus, which causes COVID-19, preferentially targets type A blood cells.

“We show that the part of the SARS-CoV-2 spike protein that’s key to enabling the virus to invade cells displays affinity for blood group A cells, and the virus in turn also shows a preferential ability to infect blood group A cells,” Dr. Sean R. Stowell, of Harvard Medical School and Brigham and Women’s Hospital, said in a press release.

Type A blood cells are more susceptible to SARS-CoV-2 infection than type O blood cells, Stowell noted. “Among a group of several thousand people, some studies suggest that those with blood group A may be 20 percent more likely to be infected after exposure to SARS-CoV-2 compared with those who have blood group O.” Subsequent experiments indicated that the Omicron variant demonstrated an even stronger preference for infecting type A blood cells than the original virus.

Other recent studies have explored the mechanisms linking blood type to susceptibility to SARS-CoV-2.  One study showed that levels of ACE2 protein, the receptor that the virus binds to for cell entry, were significantly higher in people with type A blood compared to other blood types. The researchers also found that the binding rate of the spike protein to red blood cells was highest in people with type A blood and lowest in people with type O.

Despite these associations, when assessing a person’s risk of severe SARS-CoV-2 infection, factors such as age and pre-existing chronic conditions, like heart disease, tend to have more significant effects on the risk of severe SARS-CoV-2 infection than blood type.

Increased Risk of Cancer

Pancreatic cancer is one of the deadliest types of cancer because it tends to grow quickly, can rapidly invade surrounding organs, and is often difficult to detect early. One study found a statistically significant association between ABO blood group and pancreatic cancer risk. Compared to people with type O blood, those with blood types A, AB, and B had a 32, 51, and 72 percent higher risk of developing pancreatic cancer, respectively.

Additionally, a comprehensive review found that people with type A blood were more susceptible to Helicobacter pylori, a known risk factor for stomach cancer, thus increasing their likelihood of developing the disease. In contrast, type O blood was associated with a lower risk of several cancers, including colorectal, gastric, and breast cancer.

Higher Risk of Other Serious Conditions

Blood type has been found to be associated with an increased risk of other several serious health conditions.

Increased Risk of Heart Disease

Blood type may also be linked to the risk of developing heart disease. A meta-analysis from the Harvard T.H. Chan School of Public Health, analyzing health data from nearly 90,000 individuals over more than 20 years, found that people with type O blood had the lowest risk of developing coronary heart disease. After adjusting for cardiovascular risk factors, participants with blood types A, B, and AB had an increased risk of coronary heart disease by 6, 15, and 23 percent, respectively, when compared to people with type O blood.

Increased Risk of Allergic Diseases

There is also a clear association between blood type and allergic diseases. A review found that people with type O blood were more prone to allergic rhinitis and asthma compared to those with non-O blood group. In contrast, people with non-O blood types had a higher likelihood of developing atopic dermatitis, with the highest prevalence among those with type B blood, followed by type A.

Friday, November 22, 2024

These detections via serological testing strongly suggest some additional cases have gone unidentified. How many, is unknowable.   

It takes more than a little luck for a community case  - one w ithout known contact with livestock or someone who is known to be infected - to be picked up by surveillance.  Most doctors and walk-in clinics only perform rapid flu tests (if they do a test at all), and that generally does not reveal the subtype, only if it is Influenza A positive or not. 

While there may be a heightened index of suspicion in community with outbreaks of H5N1 in cattle or poultry, in most communities mild or moderate cases can be difficult to detect. The Missouri case was only identified a week after the patient was released from the hospital.