Rat-borne diseases series: Epidemic hemorrhagic fever

“Prevent heatstroke in summer and prevent rats in winter!” This proverb means that in the hot summer, people should take measures to prevent heatstroke. In the winter, due to the reduction of wild food and the cold climate, rats will hide in residents’ houses to hibernate, creating conditions for the high incidence of epidemic hemorrhagic fever (EHF), also known as hemorrhagic fever with renal syndrome (HFRS), a highly contagious rodent-borne disease. Epidemic hemorrhagic fever is an infectious disease with a wide distribution range and a high incidence rate, especially in the northern and eastern parts of the Eurasian continent [1]. my country is the country with the most serious epidemic of EHF, especially in the northeast, east China, central and south China, and southwest China. The number of cases in my country each year accounts for more than 70% of the total number of cases in the world [2].

1. What is hemorrhagic fever?

Hemorrhagic fever with renal syndrome, also known as hemorrhagic fever with renal syndrome, is a natural epidemic disease caused by a virus of the genus Hantavirus in the family Hantaviridae. In my country, HFRS outbreaks are mainly caused by two subspecies of Hantavirus, Hantaan virus (HTNV) and Seoul virus (SEOV) [3]. These two different subtypes of Hantavirus each have a strictly single fixed rodent host, and their main host animals are the black-striped mouse and the brown rat, respectively. Therefore, the epidemic areas in my country can also be divided into three categories: the field mouse type, the house mouse type, and the mixed type [4]. The seasonality of epidemic hemorrhagic fever in my country is obvious, showing a bimodal trend. The peak seasons are spring (April to June) and autumn and winter (October to January of the following year). The spring peak is a small peak, which is also the peak season for the house mouse type. The highest incidence rate is in May or June, because this is the peak season for rodent reproduction, food is sufficient, and the rodent population density increases, resulting in a small peak in the incidence. The autumn and winter peaks are large peaks. As the temperature drops, mice enter human settlements and farmers go to the wild to work in the autumn harvest, and people have more contact with black-striped field mice and large forest mice, resulting in a significant increase in the incidence of field mice, with the highest incidence rate in November. Mixed epidemic areas have both characteristics, with epidemics in spring and autumn and winter, but the seasonal characteristics of the dominant rodent species are dominant [5-6].

2. Discovery, transmission and manifestations of hemorrhagic fever

The earliest record of epidemic hemorrhagic fever can be traced back to Northeast China in 1932. At that time, it was called "Sunwu fever" and "Black River disease", with a mortality rate of up to 30%. However, scientists at the time failed to discover its pathogen. It was not until 1978 that Korean scientist Lee Ho-wang first isolated the Hantavirus and unveiled its mystery. Through further research, the transmission routes of epidemic hemorrhagic fever were clarified, mainly including the following routes:

1. Contact transmission: Humans become infected after being bitten by rodents or having broken wounds that come into contact with virus-carrying rodent excrement or blood.

2. Transmission through the digestive tract: Eating food or drinking water contaminated by rodent excrement, the virus enters the body through the oral mucosa.

3. Respiratory transmission: Inhalation of dust containing rat excrement and the virus invades through the respiratory mucosa.

4. Vertical transmission: After a pregnant woman is infected, the virus can be transmitted to the fetus through the placenta and may cause miscarriage or stillbirth.

5. Mite-mediated transmission: Gadama mites and chiggers act as vectors to spread viruses among rats, or bite humans under certain conditions, potentially causing human infection.

After being infected with Hantavirus, most people show symptoms of latent infection, and a few will have symptoms such as fever, bleeding, and kidney damage. The incubation period is 4-46 days, generally 7-14 days, and more often than not, two weeks. Typical hemorrhagic fever patients will have symptoms of "three reds" and "three pains", namely, redness of the face, neck, and chest skin, headache, back pain, and orbital pain. They will also have symptoms such as conjunctival congestion, eyelid edema, and skin hemorrhages. The course of hemorrhagic fever is generally divided into five stages: fever stage, hypotension shock stage, oliguria stage, polyuria stage, and recovery stage. Generally, mild patients only show fever stage, polyuria stage, and recovery stage, while the first three stages of severe patients will overlap and show severe poisoning symptoms and high fever. The condition changes rapidly and may lead to death [7].

3. The current situation of epidemic hemorrhagic fever cannot be taken lightly

my country has always been the country most seriously affected by hemorrhagic fever. In the 1990s, the number of cases of hemorrhagic fever in my country was between 40,000 and 60,000 per year, reaching a peak of 62,754 cases in 1995. In recent years, with the strengthening of prevention and control measures, the incidence rate has declined. Since 2010, the number of cases of hemorrhagic fever has dropped to about 10,000 per year [8-9]. With the promotion of vaccines in hemorrhagic fever epidemic areas, the incidence rate has further decreased in the past three years, maintaining at about 5,000 cases per year. However, we still cannot take it lightly. Northeast China, North China and other regions are still high-incidence areas, and the scope of cases is constantly expanding. New epidemic sites continue to appear, and some old epidemic areas have also shown signs of rebound. The incidence rate of outdoor occupational groups such as farmers and forestry workers is still very high, and periodic fluctuations still exist. The prevention and control situation remains severe.

Image source: Pixabay

4. How to prevent hemorrhagic fever?

Epidemic hemorrhagic fever has a long course and a long recovery period. Generally, patients with hemorrhagic fever enter the recovery period 3 to 4 weeks after the onset of the disease. The recovery period is generally 1-2 months, while the recovery period for severe patients may be as long as 3-6 months, which will bring a heavy burden to patients and their families. Therefore, it is very important to prevent epidemic hemorrhagic fever. We can take the following measures:

1. Rat control and rodent control: Epidemic hemorrhagic fever is a disease spread by rodents, so rat control and rodent control are crucial. In the home, you should block the gaps leading to the outside world, such as doors, windows, and sewers, and use rat-proof boards and rat-proof nets. Clean up the piles of debris regularly, use closed trash cans, and reduce the places where rats live and the food sources. In some key places such as restaurant kitchens and food warehouses, use rat-catching tools to catch and kill rats. In old streets and communities with serious rat infestations, you can use rat poison to lure and kill rats under the guidance of professionals.

2. Pay attention to food hygiene: Food stored at home should be kept in a closed environment to avoid contamination by rodents, avoid eating raw or cold food, avoid contact with items that may be contaminated by rodents, wash hands frequently, and boil food and water for disinfection.

3. Pay attention to personal protection: When working outdoors, you should wear long sleeves and long pants and tie your cuffs and trouser legs tightly, wear protective gloves, avoid direct skin contact with objects that may carry the virus, and if you are scratched, you need to treat the wound in time and disinfect it to reduce the risk of infection.

4. Timely vaccination: The hemorrhagic fever vaccine is an important means of preventing the disease. It is suitable for people aged 16-60 years [10]. In particular, residents in high-incidence areas such as Northeast China and North China and outdoor workers should take the initiative to get vaccinated against hemorrhagic fever. The vaccine is administered in three doses. The first two doses are given 14 days apart for basic immunization, and the third dose is for booster immunization, which should be given one year after basic immunization. In endemic areas, the hemorrhagic fever vaccine is a vaccine included in the national expanded immunization program, and vaccination services are provided free of charge to high-risk groups. Vaccination can effectively reduce the risk of infection and protect the health of oneself and one's family.

References:

[1] Yang Xiaojuan, Wang Wenrui. Research progress on hemorrhagic fever with renal syndrome in my country [J]. World Latest Medical Information Abstracts,

2014, 14(7): 50-53.

[2]Zheng Zhaolei. Analysis on the epidemic characteristics and current situation of the source of hemorrhagic fever with renal syndrome in Shandong Province[D]. Shandong University, 2019(09).

[3] Wang Juan, Feng Yuliang, Zhou Xingyu, Zhou Jiushun. Analysis of epidemic characteristics of hemorrhagic fever in Sichuan Province from 2018 to 2022[J]. Journal of Preventive Medicine Intelligence, 2024, (08): 923-931.

[4]Zheng Zhaolei. Analysis on the epidemic characteristics and current situation of the source of hemorrhagic fever with renal syndrome in Shandong Province[D]. Shandong University, 2019(09).

[5] Deng Xuefei. Analysis of the epidemiological characteristics of reported cases of hemorrhagic fever with renal syndrome in China from 2004 to 2021 and the current status of the epidemic of rat-transmitted hemorrhagic fever-related viruses in Jiangxi Province from 2020 to 2021[D]. Guizhou Medical University, 2023(02).

[6] Cao Yunxian. Spatiotemporal analysis of epidemic characteristics and influencing factors of hemorrhagic fever with renal syndrome in Shandong Province[D]. Shandong University, 2023(01).

[7] Li Lanjuan, Ren Hong. Infectious Diseases (9th Edition) [M]. Beijing: People's Medical Publishing House, 2018: 92-101.

[8] Deng Xuefei, Du Shanshan, Huang Xiaoxia, Wang Qin, Li Aqian, Li Chuan, Sun Lina, Wu Wei, Li Hao, Liu Tiezhu, Tian Tingting, Wang Shiwen, Liang Mifang, Li Dexin, Xie Chun, Li Jiandong. Analysis of epidemiological characteristics of reported cases of hemorrhagic fever with renal syndrome in China from 2004 to 2021[J]. Disease Surveillance, 2023, (01): 70-74.

[9] Guo Shouheng, Gao Lidong. Analysis of the prevalence of hemorrhagic fever with renal syndrome in 31 provinces, municipalities and autonomous regions in China from 1991 to 2005 [J]. Preventive Medicine Forum, 2007, (04): 359-361.

[10] Chinese Society of Preventive Medicine, Infectious Diseases Prevention and Control Branch, Chinese Medical Association, Infectious Diseases Branch, Gao Zhiliang, Wang Guiqiang, Lian Jianqi. Expert consensus on the prevention and treatment of hemorrhagic fever with renal syndrome[J]. Infectious Disease Information, 2021, 34(3): 193-201212

Contributor: Chongqing Science Writers Association Writers: Zhou Wangpeng, intern physician, Wang Ya, deputy chief physician, and Zou Jingbo, chief technician, Chongqing Yongchuan District Center for Disease Control and Prevention Review expert: Li Hanbin Statement: Except for original content and special instructions, some pictures are sourced from the Internet for non-commercial purposes and are only used as popular science materials. The copyright belongs to the original author. If there is any infringement, please contact us to delete it.