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The secret of asymptomatic carriers: How do they hide in the crowd?
Asymptomatic carriers are people who are infected with a pathogen but show no signs or symptoms. These carriers play a key role in transmitting common infectious diseases, such as typhoid fever, HIV, intestinal Clostridium difficile, influenza, cholera, tuberculosis, and the recent COVID-19 that has attracted widespread attention. This has triggered public fears and doubts about hidden infections, especially because many carriers do not know that they have become potential sources of infection. What secrets are hidden here?
“Asymptomatic carriers pose considerable challenges in public health programs.”
Types of asymptomatic carriers
Asymptomatic carriers can be classified according to their current disease status. When an individual rapidly spreads the pathogen after infection but has not yet developed symptoms, this is called a "latent carrier." Humans can also spread the disease again after a period of illness, and these individuals, who often think they have recovered, are called "recovering carriers." Certain viral diseases, such as hepatitis and polio, are often spread this way.
"Healthy carriers" never show signs or symptoms of the disease but are still capable of infecting others.
Importance in disease transmission
Limited data on the prevalence of asymptomatic carriers makes public health planning difficult. Because disease surveillance relies on estimates of asymptomatic and symptomatic cases, a lack of carrier prevalence information can lead to inadequate public health measures. For example, a disease with a known low asymptomatic prevalence may prompt increased surveillance of symptomatic cases, whereas a higher asymptomatic prevalence may prompt more aggressive measures such as travel bans and mandatory quarantines.
Possible explanation
While the exact explanation for asymptomatic carriage is unclear, researchers are still working to understand how specific bacteria thrive in the human body in an effort to identify common mechanisms of asymptomatic transmission.
Biological mechanisms taking Salmonella as an example
Multiple studies have shown that Salmonella can survive within immune cells and alter their metabolic systems to further spread the disease. Using a closely related bacterium (S. typhimurium), scientists have been able to create a mouse model that mimics the cases of persistent salmonella observed in typhoid carriers.
"The survival ability of Salmonella is closely related to its ability to hide in anti-inflammatory macrophages."
Asymptomatic bacteriuria
Asymptomatic bacteriuria is a condition that typically affects 3-5% of women, with the most vulnerable groups including the elderly and those with diabetes. The analysis showed that among women, the risk of bacteriuria increases with age.
The infectious disease perspective
Asymptomatic carriers further spread many infectious diseases. According to the general principle in epidemiology, the 80-20 rule states that 80% of disease transmission is carried out by only 20% of the population. For example, typhoid fever, HIV, and other common infectious diseases all show this trend.
“Asymptomatic carriers play an important role in the spread of the disease.”
Conclusion
The existence of asymptomatic carriers makes the world face hidden health threats. They follow society like a shadow and affect the formulation and implementation of public health policies. As our understanding of these carriers continues to deepen, it makes people think: How can we better protect ourselves and society from such hidden threats?
