Virus family

Viruses are a kind of little life that we are familiar with but unfamiliar with. Although the new crown virus is an uninvited guest, the virus is a frequent visitor in human life. A person may be infected with hundreds of viruses in their lifetime. However, except for researchers who specialize in virology research, almost no one has actually seen the virus itself. So what exactly is a virus? What is the difference between it and another invisible organism-bacteria? Next, let us visit this strange and familiar creature-the virus.

Viruses only show signs of life when they encounter a suitable host cell

We are little parasites
We are extremely tiny microbes. Compared with the bacterial family, we are much more miniature, usually in nanometers, several orders of magnitude smaller than bacteria. The optical microscope for observing bacteria can’t see us at all, only the electron microscope with a magnification of tens of thousands of times can see our appearance. In addition to being small, our body structure is also very simple, consisting only of protein shells and nucleic acids wrapped inside, unlike other microorganisms such as bacteria, which have cell structures such as nuclei and organelles. More importantly, we are strictly intracellular parasites. If we want to maintain life, we must rely on the host cell system we are infected with. Only in the “big house” of host cells can we have enough “food” to survive and multiply. Once we leave the host cell, even if we can continue to live for a period of time, we cannot maintain normal life activities. In contrast, bacteria can live independently without the host. In the laboratory, scientists can cultivate bacteria with nutrient-containing medium, but if we want to cultivate us, we need to cultivate with cells or laboratory animals. In a nutshell, we are a peculiar non-cellular organism in the microscopic world, essentially biological macromolecules containing proteins and nucleic acids, and when we encounter a suitable host cell, we will wake up, show the characteristics of life and thrive.

My seven aunts and eight aunts
Our big family is as rich and diverse as the animal and plant kingdom. Generally speaking, this large family can be divided into human viruses, animal viruses, plant viruses, bacterial viruses (bacteriophages), etc. according to the type of infected host. Different viruses usually have corresponding hosts. For example, plant viruses can only infect plants but not animals. Viruses that infect lower vertebrates such as fish generally do not infect higher vertebrates such as mammals. Since humans are actually one of the higher animals, some viruses can infect both animals and humans, such as rabies virus.

From a more professional point of view, virologists have scientifically and systematically classified the virus families according to taxonomic levels such as order, family, genus, and species according to the biological characteristics and evolutionary kinship of different virus families. At present, there are more than 140 families of viruses, each of which can be divided into several virus genera and virus species in turn. Even in the same species, there are multiple different viruses. If the virus family is a large family composed of some viruses with similar characteristics, then the virus species is like a small family composed of members who are closer to each other within the large family.

Our diversity is also manifested in form. Generally speaking, my close relatives (viruses in the same family) tend to have similar appearances. If they are not in the same family, they will have very different styles. For example, the coronavirus has a spherical shape and looks like a crown; the rabies virus belongs to the Rhabdoviridae family and looks like a bullet; the Ebola virus has a slender body, just like the ancient Chinese “Ruyi”. The T4 bacteriophage is shaped like a sci-fi, resembling a bionic spider robot.

Coronaviruses mainly invade through the respiratory tract, and similarly there are influenza viruses

How do we “do mischief” in the human body
Infectious diseases are one of the main threats to human health, most of which are our “masterpieces.” We often adopt different “offensive methods” when invading the human body. Coronaviruses and influenza viruses mainly invade through the respiratory tract; rotavirus and norovirus are pathogens that invade through the digestive tract, which is commonly known as “disease enters the mouth”; and arboviruses such as Japanese encephalitis and dengue virus When mosquitoes bite, they will sneak into the human body; the damaged skin and mucous membranes after being bitten by a dog or scratched are the only way for the rabies virus to “attack” the human body.

The way the virus invades the host is closely related to the way the virus spreads. Generally speaking, viruses spread through the respiratory tract have a stronger transmission capacity, and the air droplets discharged from sneezing or even speech may contain viruses. Different viruses will infect different tissues and organs after invading the human body, leading to different diseases. The new coronavirus uses the respiratory system as its main target organ, causing respiratory diseases such as coughing and pneumonia. In severe cases, breathing difficulties may occur. Some viruses mainly infect digestive organs such as the gastrointestinal tract and liver, causing digestive diseases such as diarrhea and hepatitis. The rabies virus invades the nervous system, while the cunning HIV attacks the human immune system, causing the patient’s immune function defects. Severe viruses such as Ebola virus can cause severe hemorrhagic fever after infection, which is the most terrible viral disease. When we recognize a virus, pathogenicity is an important attribute of it. Many common viruses are low pathogenic viruses, such as common cold viruses, which can be cured naturally after a few days of catching a cold, but highly pathogenic viruses may kill people.

Our nemesis, defender of disease-vaccine
If a person is suffering from a disease caused by a viral infection, taking antibiotics (also known as anti-inflammatory drugs) will not work. Antibiotics treat bacteria, and they are helpless in the face of viruses. Treatment of viral diseases requires specialized antiviral drugs. Each antiviral drug has its specific target, which targets the virus in the invasion of cells, replication and other infection links, and then blocks the proliferation of the virus in the body.

Another guardian that can help fight the virus is a vaccine. Compared with the passive counterattack method of taking medicine after infection with the virus, vaccine is an active defense strategy and one of the successful methods to prevent the virus. A vaccine is essentially a biological product containing certain components of a virus. Compared with real live viruses, inactivated vaccines have lost their virulence, and attenuated vaccines have weakened their virulence. When the vaccine enters the body, the virus antigen components with it can stimulate the immune system to produce specific antibodies against the virus. When a virus comes, antibodies will quickly fight to protect humans from diseases caused by virus infection.

Rabies virus internal structure diagram

Modern vaccines have gone through more than a hundred years of development. Humans have successfully developed vaccines against dozens of viral and bacterial infectious diseases. The first extinct human infectious disease, the smallpox virus, was completely eliminated because of the vaccine. The lethal rate of rabies virus reaches 100%, but as long as the vaccine is vaccinated in time, people can be taken back from the god of death. Since the 1970s, China has formulated a nationwide immunization program, especially for children and adolescents, and the scope of vaccination has been continuously updated and expanded. Vaccines against polio, measles, hepatitis B, mumps and other viruses have been obtained. Widespread vaccination has greatly reduced the risk of people contracting the virus. Vaccines have made great contributions to preventing and curing diseases and protecting people’s health.

Refusing to consume wild animals to eliminate the source of the virus
Every two years in the world, there will be at least one new and sudden outbreak of viral infectious diseases. And the source of “most” of the viruses in these emerging infectious diseases is related to animals.

Wild animal consumption is the direct cause of many new virus outbreaks. In the process of hunting, domesticating, trading, and eating virus-carrying animals, the virus has achieved cross-species transmission from the animal host to humans. Take SARS as an example. The source of SARS is bats, but if there is no excessive consumption of wild animals, the transmission chain of “bat-civet-human” will not be formed. Although wild animals carry the virus, they are not the culprit of the disease. Game lovers and the game trade spawned from it are the real culprits. On the other hand, the destruction of the living environment of wild animals is also one of the reasons for the emergence of new viruses. The scope of human activities is accelerating and expanding, constantly infiltrating wild animal habitats. The original ecological barrier between humans and animals has been destroyed. The risk of human beings exposed to the wild animal host of the virus has increased, allowing the virus family to spread to humans. Free rider. In addition, modern social and economic development has caused changes in the ecological environment, and may also stimulate the reproduction and activity of rodents, mosquitoes and other vector animals, and become a catalyst for viral infectious diseases.

New viruses spread by different animals

Compared with passive confrontation after the outbreak, the basic disease prevention strategy is to start from the source of the virus and extinguish the flame at the starting point. Specifically, it is to reduce contact with disease-derived animals, eliminate the consumption of wild animals, and try to avoid intrusion and damage to the habitat of wild animals. In addition, before the virus shows its edge, humans can actively monitor the virus against important virus host animals and vectors such as bats, wild birds, and mosquitoes, and find and search for viruses that may cause human diseases. Find viruses before they find humans, and carry out disease prevention and control from the source.

The struggle between humans and viruses has existed since ancient times. Viruses have existed on this planet much longer than humans, and they are an important part of the natural biosphere. In the future, mankind will inevitably meet all kinds of viruses, and the game with viruses will continue. Viruses are often intimidating, but we don’t have to think of them as monsters. Because viruses are products of nature, and science can teach us how to get along with nature. Science and technology will also escort our health.