In the 19th century, there was a “killer madman” wandering around the world, whether it was in the West or the East, wherever it passed, screams and corpses were everywhere. In China, when people touch it, the whole calf from the sole of the foot to the knee becomes numb, the whole body is weak, and the dead are countless. In Europe, every ten years or so, “killers” will appear, harvesting thousands of lives. Who is the murderer, can we not arrest him?
First arrest of “murderer”
Dr. John Snow of London, England, caught the “murderer” first. In the summer of 1854, Dr. Snow’s clinic ushered in “familiar” patients again. They were pale, weak in lower limbs, cramps in the lower abdomen, and vomiting and diarrhea. Many patients died at home not long after seeing the illness, but Their families and neighbors have become new patients again.
Coronavirus
Snow decided to “track” the patients to find the “culprit” that caused them to become ill. Snow came to Soho, where the number of patients was the most, and asked about the patient’s condition and daily activities from house to house. Then, on a map of London, he marked the place of residence of the patient and the corresponding number of deaths. Snow discovered that the patient’s living area is very concentrated, and the death area is relatively concentrated. The “murderer” is only active in one place, that is, a well on Broad Street! It turns out that sewage from patients after bathing will be discharged into wells, and healthy people will get sick if they drink the well water.
Under Snow’s suggestion, the City Hall shut down the pump connecting the Browder well and the Thames. Later, London carried out a large-scale underground waterway renovation project to completely separate London’s sewage system and drinking water system. Vibrio cholerae, the “murder maniac” that has ravaged London for decades, has lost its best hiding place.
The “murderer” of London was taken home, but will it make a comeback? This is impossible to prevent, and only by finding the birthplace of the “murderer” can we truly eliminate it from the source. This problem cannot be solved with Snow’s method, after all, there is no way to track the whereabouts of patients around the world. So how should it be checked?
Molecular Epidemiology “Catch the Killer”
We know that all earth creatures, including viruses, will pass on their genetic material (genes) when replicating and reproducing, so as to “continue” their lives. After the parental gene is in the body of the next generation, mutations of varying degrees will occur to ensure its own “uniqueness.” In this way, as long as we find the pathogen with the most primitive or minimally changed genome, we will find the source.
Now, it is very easy to get the genome data of pathogens. You only need to collect a mouthful of saliva or a little blood sample from the patient and put it in the gene sequencer. In a few hours, you can obtain all the genetic maps of the pathogen. Scientists can share these data. Therefore, molecular epidemiology through genetic tracing has become a great weapon for modern disease “killers”.
In 2014, scientists at the Sanger Institute of the Wellcome Foundation in the United Kingdom used molecular epidemiology to find the birthplace of Vibrio cholerae. They collected thousands of Vibrio cholerae samples from cholera patients from different parts of the world, including those who have died, and sequenced all the samples. Then compare the differences of single bases (the basic building blocks of genes) in the genomes of different strains one by one. The smaller the single base difference between the genomes of the two strains, the closer the genetic relationship between them.
After classifying all strains according to their genetic relationship, data analysis methods are used to calculate the sequence of different gene mutations. Finally, the scientists drew a “strain development tree” diagram. On the map, we can see the genetic relationship between Vibrio cholerae in different populations in different regions, as well as their specific “separation” time.
Scientists have discovered that the bacteria in cholera patients from South Asia are direct descendants of the “ancestors.” This indicates that the origin of Vibrio cholerae is likely to be in South Asia. Further investigation found that the waters of the Bay of Bengal located at the junction of India, Bangladesh and Myanmar are likely to be the original “place of birth” of Vibrio cholerae.
Chasing Coronavirus
In 2003, humans were infected with a new type of coronavirus-SARS virus. The disease spread rapidly among people. Because of lack of immunity to it and targeted drugs, many people died of the infection. The SARS virus has never appeared in humans before. Where does it come from now? Molecular epidemiology is once again deployed to answer these questions.
The transmission route of Vibrio cholerae drawn by scientists from the Sanger Institute in the United Kingdom
Coronavirus is a type of virus that is widely found in bats and birds and other animals. Scientists divide them into 4 types. Among them, alpha and beta coronaviruses only infect mammals, and SARS virus belongs to beta coronavirus. In order to find its origin, scientists analyzed the SARS virus genome data in a variety of mammals, such as humans, bats, civet cats, raccoons, and pigs, and then analyzed the similarities and differences of each base in the genome. The historical family tree of the virus.
The analysis results show that the most similar and oldest virus to SARS virus exists in bats. If you want to find the source of SARS virus, you still have to look for it in bats. In order to find the original host of the SARS virus, Shi Zhengli’s team from the Wuhan Institute of Virology, Chinese Academy of Sciences traveled to 28 provinces and cities in China in the past ten years. In 2011, they found a group of Chinese chrysanthemum bats in a remote cave in Yunnan Province. Through sequencing and sequence comparison, they found that the SARS-like coronavirus in the bat population was very similar to the SARS virus. These viruses contain all the genetic components of the SARS virus, that is to say, it was the accidental genetic recombination of these viruses that eventually produced the SARS virus that can infect humans.
In 2020, the “close relative” of the SARS virus, the new crown virus, once again attacked humans, and scientists have not yet concluded its true source. There is a long way to go to chase down the “true murderer” of the disease, but we already have the most effective method. As long as more and more comprehensive research materials are collected, the “true murderer” will truly be revealed.
Find the cause of cancer
Molecular epidemiology can also be applied to the research of chronic non-communicable diseases like cancer.
Cancer is a chronic disease, which can last for decades from exposure to carcinogens to cancer. At present, all over the world, especially in developed countries, cancer has been one of the main causes of human death.
Cancer occurs mainly because body cells are stimulated by environmental factors such as chemical factors (such as aflatoxin, arsenic and other chemical carcinogens), physical factors (such as radiation) and biological factors (such as hepatitis B, HIV virus) and other factors , Causing changes in the genetic material of genes and triggering cell proliferation, causing normal cells to develop into cancer cells. Cancer cells will continue to proliferate and affect normal physiological functions, eventually taking life.
The process of carcinogenesis can generally be divided into three stages: initial stage, promotion stage and expansion stage. Each stage is likely to be caused by different external environmental factors and different internal factors, and involves many different biochemical mechanisms and genetic genes. At present, there are many genotoxic carcinogens that can directly or indirectly bind to macromolecules in cells such as chromosomes, ribonucleic acid, and proteins. Such combination may cause gene mutations, abnormal gene expression, and other genetic abnormalities. possibility.
Therefore, we can use the latest biotechnology such as monoclonal antibodies and immunological methods to quantify the bonding of a certain chemical carcinogen to intracellular macromolecules to establish the relationship between a specific chemical carcinogen and human cancer. . This method can also be used to find people with special constitutions, that is, they are particularly sensitive to certain chemical carcinogens. Therefore, this kind of molecular epidemiology research can provide a lot of valuable information about the cause of cancer, and can be used as a reference for preventive measures.
