As poet Luo Yin of the late Tang Dynasty put it, "Mosquitoes are poisonous and consume human muscle." While mosquitoes obviously don't eat human flesh, this expression reflects their role as carriers of pathogens responsible for disease transmission. This article delves into the details of this omnipresent "little assassin"—mosquitoes.
I. A Closer Look at Mosquitoes
Mosquitoes belong to the order Diptera and the family Culicidae. Colloquially known as "mosquitoes," they are among the most significant groups of insects in medical science. Mosquitoes are found worldwide and exhibit remarkable diversity. To date, researchers have identified 3 subfamilies (Toxorhynchitinae, Anophelinae, and Culicinae), 35 genera, and over 3,600 species or subspecies globally. In China, scientists have documented more than 370 species, with over half belonging to the three predominant genera—Anopheles, Culex, and Aedes.
The mosquito's life cycle consists of four distinct stages: egg, larva, pupa, and adult. Typically, the developmental timeline is about 1–2 days for eggs, 5–7 days for larvae, 2–3 days for pupae, and 3–7 days from adult emergence to egg-laying after blood-feeding. The complete cycle takes roughly 1–2 weeks. Mosquitoes are therefore referred to as insects that undergo complete metamorphosis.
II. Dangers of Mosquitoes
(I) Disease transmission: Mosquito-borne diseases are epidemic illnesses of natural origin spread by vector mosquitoes. Common examples include brain fever (Japanese Encephalitis/JE), malaria, dengue fever, filariasis, yellow fever, and other highly dangerous infectious diseases. Take brain fever, also referred to as "Japanese encephalitis," as an example. This is an acute infectious disease affecting the central nervous system, characterized by inflammation of the brain parenchyma as the primary pathological feature.
(II) Unbearable itching: The most apparent harm caused by mosquitoes is the itching sensation they induce, which can be incredibly aggravating. When bitten by a mosquito, the affected area quickly swells into a red bump, accompanied by itching. Scratching the area with hands can break the skin, increasing the risk of infection and potentially leading to more severe skin conditions.
III. Primary Mosquito Species that Spread Infectious Diseases in China
(I) Anopheles sinensis
Adult mosquitoes are medium-sized and have a gray-brown coloration. The antennae feature four white bands, with the widest band located at the tip. The mesothoracic scutum displays five faint longitudinal stripes and is adorned with sparse yellowish fine hairs, while the abdomen appears gray. In China, it is primarily found in regions along the 10°C average temperature line. The main habitat of Anopheles sinensis consists of natural clear water, still water, and stagnant water environments. Anopheles sinensis is one of the primary vectors of malaria and filariasis, and it is also capable of transmitting the brain fever.
(II) Culex pipiens pallens
The adult Culex pipiens pallens is medium-sized, light brown, with dark brown proboscis and legs, lacking any white rings or stripes on the mesothorax. It predominantly breeds in moderately polluted stagnant water near human settlements. Culex pipiens pallens is predominantly found in northern regions. The emergence of larvae occurs later as latitude increases. In southern Jiangsu, Zhejiang, and other southern areas, there are two peak seasons annually, occurring in June–July and October–November. In northern and northwestern regions, its peak season is observed from July to August. Culex pipiens pallens has been identified as the main mosquito species responsible for blood-sucking nuisance in northern China and as the primary vector of Bancroftian filariasis, with an infection rate reaching up to 50%.
(III) Aedes aegypti
The dorsal side of approximately one-third of the female mosquito's antenna tips is white; a pair of white scale clusters can be found at the base of the proboscis; vertical forked scales are present on the crown of the head. This species is predominantly found in Guangdong, Guangxi, Yunnan's Xishuangbanna, and Hainan regions of China. Aedes aegypti primarily inhabits small pools of stagnant water in and around human settlements. It is a known vector for transmitting diseases to humans and animals, including Eastern equine encephalitis, Western equine encephalitis, and Venezuelan equine encephalitis, through its bite. As a result, Aedes aegypti is widely regarded as one of the most dangerous mosquito species worldwide.
(IV) Aedes albopictus
Commonly referred to as the "Asian tiger mosquito," it possesses entirely dark antennae and features a silvery-white vertical stripe down the center of the scutellum. Its larvae are typically found breeding in rain-filled tree holes. Originating from Southeast Asia, this mosquito species has now spread globally to tropical, subtropical, and temperate regions and is widely distributed across China. It serves as a secondary vector for transmitting dengue fever and chikungunya in Southeast Asia and is one of the primary vectors responsible for the spread of dengue fever in China.
IV. Countermeasures by the Customs
To prevent imported pests like 'little assassins' from sneaking into the country, customs authorities have rigorously implemented the Biosafety Law of the People's Republic of China. They have recognized the critical importance and urgency of enhancing biosecurity measures at customs, prioritizing monitoring efforts at border ports, and against imported vectors. Meanwhile, the Port Public Health Risk Monitoring Plan (Global Infectious Disease Epidemic Port Vectors) has been developed to enhance the scientific rigor and efficiency of monitoring. This initiative aims to ensure early identification, timely warnings, and swift responses, thereby fortifying port quarantine defenses and steadfastly safeguarding the nation's borders.
Customs vector monitoring adheres to the 'four determinations' principle: determine the personnel, scheduling, habitats, and methods. Adult mosquitoes are captured using carbon dioxide lamp traps. Monitoring is conducted once during the early and late ten-day periods of each month, beginning at sunset and lasting for two hours each session. Egg traps are employed for monitoring Aedes. Conduct monthly monitoring by placing 50 egg traps at each monitoring point, ensuring a minimum spacing of 10 meters between each trap. Keep the traps in place for 7 consecutive days, and check and document the Aedes monitoring results on the 4th and 7th days. After collecting vector specimens, promptly conduct identification, prepare specimens, and take photographs. Immediately collect samples for pathogen testing and, adhering to biosafety control protocols, deliver them to the nearest laboratory for testing as soon as possible while maintaining thorough records.
(The author is employed by Urumqi Customs)
Disclaimer：The above content is translated from Chinese version of China Inspection and Quarantine Times. The China Inspection and Quarantine Times version shall prevail.