The tick crisis under a warm and humid climate

Author: Zhou You

Published in the 2023th issue of China Newsweek magazine on August 8, 21

Smaller than sesame, it feeds on animal blood, and if it senses animal activity around it, it will come to the top of the blade of grass, open a pair of forelimbs to "embrace the sun", and then grab the clothing or fur of the "prey", cut the skin with the mouthparts and look for blood vessels, bury half of its body in the wound, and enjoy the "deliciousness", this veritable "vampire" is a tick.

When ticks bite, they can climb on the surface of a person or animal for up to ten days. The size of the tick that is "full and drunk" will expand dozens of times, and a "mole" the size of a soybean can be formed on the human body surface. In the process, people may also be infected with the new Bunya virus, which ticks carry. After people are infected with the virus, they may develop fever with thrombocytopenia syndrome (hereinafter referred to as fever), infected people have persistent fever symptoms, severe cases will have thrombocytopenia, white blood cell levels will decrease, causing shock and multiple organ failure, and eventually death.

In the past two years, there have been many cases of death from tick bites across the country, and fever accompanied by this disease will also occur "human-to-human" transmission. In July, Zou Yang, chief physician of the Beijing Institute of Tropical Medicine of Beijing Friendship Hospital, told the media that this year, the institute received 7% more tick bite cases than in the same period of previous years. It is important to be aware that under the influence of climate change, the range of tick activities is expanding worldwide, and everyone may be exposed to the risk of this "vampire" bite.

Saliva is a secret weapon

Ticks, known as "grass reptiles" and "ticks", are an ectoparasite. Zou Yang told China Newsweek that in addition to the Beijing case, the proportion of patients admitted by hospitals across provinces such as Hebei, Henan and Shandong has also increased this year. Typical symptoms in the early stages include skin damage caused by insect bites, redness, swelling, heat and pain, generalized rash throughout the body, and unknown fever.

Fever is a serious illness caused by tick bites, common in China and also known as tick disease. An expert from the Chinese Center for Disease Control and Prevention explained to China Newsweek that fever is accompanied by zoonotic diseases, the main clinical manifestations are fever, thrombocytopenia, leukopenia, accompanied by gastrointestinal symptoms, and severe cases of multiple organ failure, bleeding, shock, etc. In 2009~2010, there were large-scale tick bite deaths in six provinces including Henan, Hubei and Shandong in China. According to the Institute of Virus Prevention and Control (IVDC) under the China Disease Control and Control, as of September 2010, a total of 9 patients with suspected fever and hospitalization in six provinces, of which 241 were confirmed and 171 died.

In 2010, the National Health Commission issued technical documents such as the Guidelines for the Prevention and Treatment of Fever with Thrombocytopenia Syndrome. According to IVDC data, the disease can be traced back to 1996, with 11 clusters and 2 deaths in Yixing City, Jiangsu Province, mainly by the longhorned blood tick. The longhorned blood tick is widely distributed in China, mainly in hilly, mountainous and forested areas. People can become infected through contact with the blood, body fluids, and environments and objects contaminated by them. In June this year, data released by Beijing CDC showed that as of 6, the number of fever associated with cases in China has reached 2021,18902, and the overall case fatality rate has reached 5.11%.

Bao Xianjun is the director of the Institute of Acute Infectious Disease Prevention and Control at the Jiangsu Provincial Center for Disease Control and Prevention, and has also been the victim of tick bites. He recalled to China Newsweek that during a tick picking job in the field, he failed to hold his tweezers steadily, allowing a tick to escape, and he could not find it. At that time, I didn't feel anything, but after three days I went home to take a bath, I scratched my neck, noticed that "it didn't feel right", and found that a tick was attached, which was likely to be the "tick that slipped through the net" three days ago. Fortunately, it did not cause infection. "Tick bites are very insidious He reminded.

Due to the insidious nature of bites, most people find ticks that have been "feasting" on their bodies for more than 24 hours. Many patients notice that there is an unexplained "mole" on their body and cannot be removed, only to realize that they have been attacked by ticks. Zou Yang pointed out that this gives many pathogens carried by ticks an opportunity.

This insidious nature has a lot to do with the saliva of ticks. In the process of "battling" with the host, the tick has evolved a secret weapon that is extremely beneficial to persistent bites: anti-inflammatory proteins in saliva. According to a 2019 study published in the journal Ticks and Tick-borne Diseases, when bitten by a foreign object, human tissues release signaling proteins called "cytokines" that trigger the body's immune response. However, a variety of anti-inflammatory proteins contained in tick saliva can preemptively bind cytokines and inactivate them, that is, block the immune process at the bite site, allowing the tick to continue to bite the host "safely".

Therefore, the American "Atlantic Monthly" likened tick saliva to "luxury cars carrying various pathogens", while anti-inflammatory proteins "rolled the red carpet" for the invasion of various bacteria, viruses and parasites. What's more deadly is that these anti-inflammatory proteins can repeatedly change their structure within a few hours, making it impossible for the immune system to recognize and track them, and it is difficult to generate antibody tissues to effectively resist.

In addition to its invisibility, the threat of ticks to people is also their high risk of causing severe disease. Zou Yang pointed out that fever is accompanied by a high incidence in people over 40~50 years old, and the risk of severe disease is high in people with underlying diseases, the elderly, and immunocompromised people. With some exceptions to short-term immunity after illness, lifelong immunity to the novel Bunia virus has not been found, so fever is associated with the risk of multiple infections.

Chai Yueyang, attending physician of the Department of Emergency Medicine of the Second Affiliated Hospital of Zhejiang University School of Medicine, told China Newsweek that if the patient has a history of tumor, diabetes, rheumatic immune deficiency, etc., combined with the new Bunia virus infection, it is likely to rapidly progress to severe disease. The unpredictability of the condition after severe disease will be greatly improved, some patients die within 24~48 hours, and some patients have repeated aggravations after one week of stabilization. Therefore, early and timely treatment and treatment are an important part of blocking infection.

A report released by IVDC in 2021 pointed out that there is no specific drug or specific treatment for fever. Clinically, it is mainly symptomatic and supportive treatment to prevent complications. A researcher at the School of Pharmacy at the University of California, San Diego, told China Newsweek that the variety of anti-inflammatory proteins contained in tick saliva iterates rapidly and is likely to exceed the speed of human vaccine development. Therefore, "tick disease" specific drugs are difficult to achieve, both in theory and practice. There is also no effective vaccine for fever partners in the world.

Fever is accompanied by a high case fatality rate at the beginning of the "debut". Bao said that in 2010, the local case fatality rate in China could reach 30%, and in Japan it could reach 50%. However, due to insufficient diagnostic methods, most of the patients with severe disease were found at the beginning, and relatively few patients with mild disease were found, resulting in a high case fatality rate. With the gradual improvement of the understanding of the disease, the local case fatality rate has mostly dropped to less than 10%.

At the same time, he stressed that the tick itself carries the new Bunia virus is not high, Jiangsu Province disease control surveillance data shows that the positive detection rate of the virus in ticks is about 1%, from the national perspective, in recent years, the reported incidence is up to <> per million. According to the National Health Commission, the national incidence rate is one tenth of AIDS.

In recent years, there have been many cases of "tick disease" cluster infection caused by "human-to-human" transmission in China. According to media reports, in April this year, a septuagenarian in Shaoxing, Zhejiang Province, died of a tick bite while picking tea in a tea field, and four family members were infected and hospitalized a few days later. In May last year, an elderly man in Xinyang, Henan Province, died after being bitten by a tick, and a day or two after the funeral, two other elderly people who helped him clean his body and change his life clothes developed symptoms of high fever, followed by pain, convulsions, and confusion, and soon died tragically. The grandson of one of the elderly people later suspected that he may have been infected during the process of removing a urinary catheter and dressing the deceased.

The IVDC report clearly pointed out that the blood of patients in the acute stage, as well as the blood and body fluids of patients who died of the disease, contained the new Bunya virus, especially severe patients often have coagulation mechanism disorders, severe bleeding, and are highly contagious. Nosocomial infections may occur by medical staff rescuing and caring for critically ill patients. Family members, caregivers, and funeral workers who care for patients can become infected as a result of daily braching or handling remains.

However, Chai Yueyang said that although "human-to-human" transmission has a certain chance, the public does not need to worry or panic too much. "'Human-to-human' transmission is only possible in certain very exceptional circumstances, such as when one's own skin is broken or mucous membranes come into contact with a patient's blood." He explained. Tick disease transmitted by blood alone is less prevalent than saliva-borne by rabies virus.

The risk of bites is expanding

June ~ September every year is the high incidence of tick bites, and it is also the peak period for hospital admissions. Zou Yang felt that in recent years, the frequency of hospital visits during this period has increased from one case in two or three days to four or five cases a day. From the perspective of Beijing, Daxing and other southern districts accounted for the majority of patients, but now the number of patients from Haidian, Mentougou, Changping, Pinggu and other areas has increased significantly. She believes there may be a growing trend of overall bite risk nationwide.

A 2021 study published in Nature Communications confirms her speculation. Researchers at the Beijing Institute of Microbial Epidemiology studied the spatial distribution of ticks and tick-borne diseases in China and found that temperature seasonality and average temperature of the driest season are the two most important factors affecting tick risk. Climate change, especially warming and humidification, may have triggered a sustained geographical expansion of tick species, with the overall high-risk area range of the 19 tick species found in the country increasing significantly from 1950 to 2018. A total of 393 counties and 2 million people in China are currently at potential risk of infection from a variety of tick-borne diseases, with the main high-risk areas being Central and East China, especially Henan, Shandong, Anhui, Jiangsu, Zhejiang, Hubei and Liaoning.

Zou Yang analyzed that the warming and humidification brought about by climate warming and humidification generally created a more suitable environment for tick activity and reproduction, and the distribution density of ticks increased, and the overall risk of disease transmission would increase. Other studies suggest that climate change may shorten the interval between generations of pathogens carried by ticks, accelerating their adaptive evolution and making them more aggressive towards animals and people. At the same time, rising temperatures can make ticks more inclined to choose humans as hosts.

Climate change is also indirectly increasing the risk of human bites by changing human behavior. In a 2021 article, the Annals of Entomology pointed out that global warming has increased the time humans spend participating in outdoor recreation, summer cooling and other activities, further aggravating the risk of infection in humans.

As ticks begin to migrate to higher latitudes and urban green spaces, experts warn that it's not just fever that accompanies this tick-borne disease that people need to be wary of. "Its practical term 'tick disease' to refer to fever is inaccurate." Bao Xianjun emphasized. In his view, fever is only one of the diseases transmitted by ticks, and the two are mixed in China to facilitate communication.

Ticks exist on all continents and are the second largest pathogen vector in the world after mosquitoes, transmitting a wide range of diseases, carrying pathogens including bacteria, viruses, rickettsia, spirochetes, parasites and other 5 categories of more than 220 species, covering 83 viruses, 14 bacteria, 17 spirochetes, 32 protozoa. A tick can carry two or more pathogens at the same time, posing a risk of infection from multiple diseases. In addition to the fever associated with the novel Bunya virus, the more serious diseases caused by ticks include forest encephalitis, spotted fever, and Lyme disease.

"Some diseases are characterized by occupational diseases." Zou Yang said that many tick-borne diseases are obviously regional. For example, forest encephalitis is common in the Daxing'anling Mountains in Northeast China and Inner Mongolia, and fever is often associated with in Jiangsu, Zhejiang and North China. This is related to the distribution of ticks and pathogen species endemic in the area, but it is more important to note that foresters, field workers, herders, etc. have become high-risk groups for tick-borne diseases. Chai Yueyang also reminded that field workers may pay less attention to the body surface, it is not easy to find the worm body, and the tick bite has no obvious itching and pain, so it is easy to ignore the bite history.

According to public information, the Daxing'anling forest area in Inner Mongolia is a natural foci of forest encephalitis. Forest encephalitis is also known as "tick-borne encephalitis", Han Shuzhen, deputy director of the Institute of Tick-borne Diseases and chief physician of the Department of Neurology of Inner Mongolia Forestry General Hospital, mentioned in an interview with the media in July this year that in the Daxing'anling area, the average number of tick bite visits per year is about 7~2000. Among them, patients with medium and severe forest encephalitis will have features of nervous system involvement, such as severe headache, meningeal irritation, seizures, limb paralysis, puphoric signs, and even mental symptoms such as cognitive impairment. The case fatality rate of forest encephalitis can reach 3000%~10%.

In addition to carrying pathogens, ticks can also make some otherwise harmless substances labeled as "enemies" by the human immune system. Recently, the New York Times published the latest research results of the US Centers for Disease Control and Prevention this year, saying that more than 45,15000 people in the United States suffer from α-galactose syndrome (AGS) caused by lone star ticks, and the number of new suspected cases exceeds 2009,2010 every year. AGS patients are allergic to red meat, causing red rash, itching, gastrointestinal discomfort and other symptoms after eating pig, beef, and mutton, and severe convulsions and syncope. However, these symptoms appear suddenly after a meal, and patients usually have no history of red meat allergy. The disease began to be frequently reported in the United States and Australia in 2021. In <>, Peking Union Medical College Hospital confirmed Asia's first case of AGS caused by the bite of a longhorned blood tick. Wen Liping, deputy chief physician of the allergy department of Peking Union Medical College Hospital, once told the media that as of <>, the hospital has diagnosed and treated more than ten cases of the disease.

The latest research shows that α-galactose, which triggers AGS, is widely found in red meat. After ticks bite livestock, α-galactose remains in saliva, and if they continue to bite humans, the α-galactose carried in saliva is injected directly into human blood, and then considered an invader by the human immune system, and specific IgE antibodies are produced, which are "recorded", and the next time red meat is ingested, it will trigger a series of allergic reactions.

How to prevent it scientifically?

The insidious nature of tick bites and the insect activity caused by climate change are setting the stage for accelerated spread of tick-borne diseases. According to several experts, tick bite diseases are more common than other vector-borne transmission routes such as bee stings, mosquitoes or ant bites. However, there is an incubation period after being bitten by a tick, and for most people, it usually takes about seven to ten days to become ill, and if it is not sent to the hospital in time or the early symptomatic treatment is not treated, it may lead to deterioration of the condition. In real diagnosis and treatment, because the early symptoms are close to cold and fever, there is often the possibility of misdiagnosis or delay in the timing of diagnosis and treatment, and vigilance is required.

"Generally, there are many patients with fever to be investigated in the emergency room, which may account for 20%~30%, and there are many causes of fever, and if there is no clear traceability, tick-borne diseases have a certain hidden and missed diagnosis." Chai Yueyang said. He also said that many patients come to the doctor because of unknown fever and long-term fever, and some have been treated with broad-spectrum antibiotics before, but the effect is little because they are not symptomatic.

What are the particularities of tick bite symptoms? Chai Yueyang further pointed out that compared with the local symptoms of mosquito bites, a major feature of tick bites is that their systemic symptoms are more significant, in addition to skin allergic reactions, they may be accompanied by anaphylactic shock, systemic neurological symptoms, etc. Another feature is that the blood test found that the inflammatory indicators are relatively low, which indicates that there is a problem with the functioning part of the immune system. In addition, different viruses carried by ticks also cause different symptoms, such as fever accompanied by thrombocytopenia, liver and kidney function damage, etc., combined with the above points, in order to effectively confirm the diagnosis.

In recent years, the number of outdoor hiking and camping enthusiasts has increased, becoming a high-risk group for tick bite diseases, and scientific precautions need to be taken when approaching green spaces because of work or hobbies. Bao pointed out that there is currently a lack of insecticides specifically targeting ticks, and for environmental and biodiversity considerations, it is difficult to eliminate the risk of exposure to ticks in the wild through the large-scale use of broad-spectrum insecticides. Therefore, when going to high-risk areas in the wild where ticks may appear, it is recommended to wear long-sleeved pants, tighten the cuff legs, and use repellents to prevent bites from the source. If worms are found on the body surface or clothing, remove them in time; If you develop fever after exposure to ticks, especially if you have superficial lymphadenopathy, such as swollen inguinal and axillary lymph nodes, you should seek prompt medical attention.

Zou Yang also called for the first time to establish a sense of prevention in response to ticks. If going to a wild area with a clear tick activity and corresponding history, do not wander among the trees and avoid sitting on the grass. When the tick is about 20 cm away from a human body or livestock pet, it can sense the carbon dioxide smell of the target "prey" and jump to its surface. In addition, try to tighten the cuffs, trouser legs, collar, and wear light-colored smooth fabric when going out. Ticks tend to be more inclined to darker and brighter colors, while smooth fabrics reduce the chance of ticks adhering to clothing. Ticks like to attach to areas of the body surface that are hidden and moist, with strong odors, such as people's armpits, behind ears, groin, etc., so it is necessary to tie the neckline, two cuffs, two trouser legs, and avoid sandals and skin exposure. After going out and returning home, it is recommended to shake the clothes all over and shake the worms that may be attached to the outside of the house.

She also said that pets can also be accomplices in "attracting ticks into the house", especially dogs with rich hair, which are prone to hiding ticks. Therefore, after walking the dog, it is recommended that the owner check the position behind his ear, pinna, etc., to reduce the risk of indoor infection. According to media reports, there have been many cases of human tick infection caused by pets in Japan and South Korea.

Zou Yang reminded that after people find tick bites on the body surface, they should avoid "violent operations" such as pulling hard or burning cigarette butts. She suggested that it is best for people to always have erythromycin eye ointment at home, squeeze the ointment to the tick after finding the tick and completely cover the worm body for more than 30 minutes, so that it enters asphyxiation paralysis until death, and then prepare a flat-mouthed pointed tweezers, insert it between the tick and the skin in parallel, and remove the worm body vertically upwards. After removal, the integrity of the worm is checked, and if the head is found to be incomplete, it indicates that there is mouthparts residue on the body surface. At this time, while local disinfection, observe for two or three days, if scars or scabs are formed, it means that it has healed itself. If the skin is persistently red and swollen, you should go to the hospital for management.

She also stressed that removing the worm body is not the last step in emergency management, and that the bite area should be disinfected with alcohol or iodophor for three consecutive days to prevent residual pathogens. "There was a patient who did not have any abnormalities in the skin after the worm body was successfully removed, but there was no continuous local disinfection, and after two or three days, local redness and swelling and even ulceration appeared." She gave an example. At the same time, do not "vent anger" on the removed worm. Tick body fluids carry a variety of pathogens, and females may also carry larvae, and the risk of infection is increased by twisting the body with her fingers, causing fluid splashes that accidentally touch the mucosa of the eye or wounds on the body surface.

Zou Yang said that the prevention and treatment of tick-borne diseases should stand from a global perspective. In Beijing, for example, in addition to domestic "imported" cases from various provinces in China, major hospitals may also accept cases from abroad. Beijing Friendship Hospital has consulted cases of babesiosis imported from the United States, which is also a microbial pathogen carried by ticks, which is endemic in the Midwest and coastal areas of the United States, but rare in China, with clinical manifestations similar to malaria, and may cause multiple organ failure in severe cases. "Some rare tick pathogens may be imported from abroad, and we need to constantly update the pathogen species and take systematic precautions against tick-borne diseases." She said.

At present, although fever is not a statutory infectious disease, the "consensus" of medical and health institutions at all levels is to refer to the report of Class B infectious diseases, and once a case is found, it needs to be reported directly through the network within 24 hours through the national disease surveillance information reporting system. A number of experts pointed out that since the disease is not clearly included in the types of statutory infectious diseases stipulated in the Law on the Prevention and Control of Infectious Diseases, it is understandable that even if some medical institutions do not report it, this is not conducive to the in-depth understanding of the disease in academia and the prevention and control of the population. Bao Xianjun hopes that in the future, the country will gradually include tick-borne diseases such as "tick disease" into the legal level for management, so as to strengthen the awareness of prevention and control and deepen public awareness.

China Newsweek, Issue 2023, 31

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