Since the beginning of winter, the new crown epidemic in Xi'an has not yet subsided, and many cases of hemorrhagic fever have been reported. Epidemic hemorrhagic fever, also known as hemorrhagic fever with renal syndrome, is an acute infectious disease caused by Hantavirus infection, which mainly manifests as fever, hemorrhage and kidney damage.
Hemorrhagic fever is a common infectious disease in winter and spring in northern China. Rodents such as rats are the main source of infection. Humans are mainly infected by contact with the excrement and secretions of rats. Hemorrhagic fever was recorded in Northeast my country in 1930. From 1950 to 1955, the number of hemorrhagic fever cases recorded in my country was only double digits; in 1972, the number of recorded cases exceeded 10,000. In the past five years, about 10,000 haemorrhagic fever cases have been reported in China each year, accounting for about 80% of the global reported cases.
Epidemiological evidence suggests that humans are at higher risk of contracting disease in cities and urban villages with high population densities and poor health care facilities.
Some experts once wrote that the rapid urbanization process will prolong the duration of the epidemic of hemorrhagic fever in my country. The historical change in the number of hemorrhagic fever cases is a microcosm, and many studies have shown that urbanization is closely related to zoonotic infectious diseases.
Animals affect human life
Ding Xueliang, an expert on the Academic Committee of the Global Think Tank (CCG), believes that infectious diseases are closely related to animals. The epidemic of infectious diseases is brought about by the process of human civilization. In order to become a disease that causes extensive and profound harm to human beings, some basic conditions must be met.
According to W.McNeill, an American social historian, there are 65 diseases shared by humans with dogs, 50 with cattle, 46 with sheep, and with pigs. There are 42 diseases in China, 35 diseases comorbid with horses, and 26 diseases comorbid with poultry - these diseases are basically transmitted to people by germs from animals.
In primitive societies, humans lived by gathering and hunting, and did not live with animals. Moreover, the population at that time was small, and each safari group was only a few dozen people. The groups are relatively independent, and there is no close and frequent contact. This objectively makes humans less susceptible to animal-derived infectious diseases, and infectious diseases are difficult to popularize. In the period of agricultural civilization, human beings began to live together and domesticate wild animals. Since then, animals began to closely influence human life.
Animals are hosts of many parasites and viruses. When humans live with animals, the possibility of humans suffering from animal-borne infectious diseases is also much higher. Some infectious diseases of animal origin can be infected by human contact with animals. For example, people can become infected with hantavirus from contact with mice that directly carry the hantavirus, causing hemorrhagic fever.
In addition, humans may also transmit the virus from animals through other means, including feces, saliva, eating, the carcass of sick animals, and contaminated aerosols. Among them, feces can carry a large number of bacterial viruses. Aerosols are formed when animal feces are dispersed in the human living environment or polluted with dust. The accumulated garbage provides a paradise for mosquitoes, flies and rodents.
From villages to towns, the communication between urban and rural areas has become more and more closely, cross-propagation between species has become more frequent and rapid, and humans are closer to viruses and bacteria on animals.
Why are some pathogens from animals harmless to animals, but can cause harm to humans? In long-term evolution, animals already have antibodies that can defend against such pathogens. But humans have never been infected with such pathogens before, and once infected, the body's immune system fails.
According to public information, 60% of human infectious diseases come from animals. For example, AIDS comes from monkeys, smallpox comes from rinderpest, plague comes from mice, rabies comes from dogs, roundworm comes from pigs, and malaria and dengue fever come from mosquitoes.
Positive and negative effects of urbanization
So, is it the fault of urbanization that humans suffer from animal-borne infectious diseases? Numerous studies have shown that urbanization has two opposite effects on the outbreak of animal-borne infectious diseases.
On April 24, 2020, in Nantong City, Jiangsu Province, community volunteers hang mosquito killer lamps in the green belt of the area where mosquitoes and flies are easy to breed.
On the one hand, with the improvement of sanitary conditions, medical prevention and control measures, etc., the incidence of some infectious diseases has dropped significantly.
In the early days of the founding of New China, under the guidance of the "prevention first" and other health work guidelines, our country carried out the first health revolution, and controlled and eliminated some serious infectious diseases. At the time, there were about 5,700 infectious diseases per 100,000 people in the Shanghai area; by the end of the 20th century, that number had dropped to 330. Starting around 2011, in response to hemorrhagic fever, Huangdao District of Qingdao City reported fewer and fewer cases by increasing the rate of rapid diagnosis, standardizing referrals, preventing rodents and extermination, expanding the coverage of vaccines, and popularizing knowledge.
On the other hand, people are pouring into cities, and the population is becoming more and more dense. It is necessary to expand the urban area, reclaim wasteland and log trees, build buildings and roads, which has changed the living environment of animals. People are taking more and more efficient means of transportation and enjoying more and more convenient logistics, and all things are more and more closely connected. All of this has also created conditions for the occurrence and spread of contagion.
In the process of urbanization, some infectious diseases that have been well controlled have relapsed, such as tuberculosis, influenza, and meningitis. Epidemiological evidence suggests that humans are at higher risk of contracting disease in cities and urban villages with high population densities and poor health care facilities.
everything is changing
Along with urbanization, animals are also evolving. Dr. Li Yiji from Southern Medical University has studied dengue fever in Guangzhou and found that environmental changes caused by urbanization have a great impact on the ecological characteristics of Aedes albopictus. Aedes albopictus is one of the main vectors of dengue fever. It bites humans and other animals and can transmit the virus from animals to humans.
Originally, it was believed that Aedes albopictus mainly originated from forest edges, such as tree holes and bamboo holes. But now the mosquito larvae are well adapted to urban and suburban environments, surviving on waste tires, ceramics and water storage containers. Moreover, there are more habitats suitable for the growth and development of Aedes albopictus larvae in the city, and there are more blood-sucking hosts. With the use of chemical insecticides, mosquitoes have developed varying degrees of resistance to insecticides.
These animals adapted to urban life gather in urban parks, suburban green spaces, corners of buildings, etc., and even live with humans for a long time inside and outside the house, bringing hidden dangers to the occurrence and spread of infectious diseases.
Some new infectious diseases are also emerging, such as Ebola, Severe Acute Respiratory Syndrome (SARS), Avian Influenza, Middle East Respiratory Syndrome (MERS) and Novel Coronavirus Pneumonia (COVID-19). Moreover, in the process of passing the virus from animals to humans, mutations may occur. SARS, Ebola, MERS, etc. have all mutated. Viruses are also adapting to cities and humans.
In 1978, China's urbanization rate was 17.92%. In 2020, the urbanization rate of China's permanent population will reach 63.89%, and the number of cities will reach 687. The outline of the "14th Five-Year Plan" proposes to comprehensively promote the construction of a healthy China, and we look forward to a new round of "sanitation revolution" to make cities more livable.
