This little bug's "kiss" may have troubled Darwin throughout his life...

In 1835, the 26-year-old Darwin followed the warship "Beagle" to South America. The ship sailed to the Pampas of Argentina, crossed the Luxan River, and spent the night in Luxan Village. That night, Darwin was bitten by a black insect . He recorded in his diary: "I was attacked by an insect, a kind of assassin bug. When an inch-long, soft, wingless black soft insect crawled on my body, it felt so disgusting."

HMS Beagle in South America | Wikimedia Commons

"Before sucking blood, their bodies are flat, but after sucking blood, their bodies become round and easy to crush. This kind of insect can be found in Peru and Chile . If someone puts it on the table and extends a finger over it, the insect will rush over to suck blood, but the wound is not painful. Less than ten minutes after sucking blood, their bodies change from thin sheets to round balls. Thanks to the 'blood feast' provided by a certain officer, it has been fat for more than four months, and only two weeks later, it is eager to try to suck blood again."

Triatomine bug nymph sucking blood | Wikimedia Commons

Unromantic kissing bug

Darwin and the officer who "tested the insects with his hands" did not know that this black assassin bug was a carrier of a pathogen of a deadly disease . Later taxonomists named it Triatoma infestans, which is commonly known as kissing bug in English. It is called this name because this insect bites people's faces and lips when they are asleep.

The harassing cone bug belongs to the genus Triatoma of the family Assassinidae in the class Insecta. There are more than 130 known species of the genus Triatoma, most of which feed on the blood of vertebrates , and a few species suck the blood of other invertebrates. The genus Triatoma is mainly distributed in the Americas, with a few species also distributed in Asia, Africa and Australia.

Harassing adult triatomine bugs | Bärbel Stock / Wikimedia Commons

The harassing cone bug is an insect with incomplete metamorphosis, and it goes through three stages in its life: egg, nymph, and adult . A female insect that is full of blood can lay 100-600 eggs in its lifetime. They often lay their eggs in cracks in the walls or roofs of houses, or in the nests of vertebrates. The eggs hatch into first-instar nymphs of about 2 mm. The nymphs have no wings and have flat bodies. At this time, they can suck blood. After that, the nymphs continue to grow by sucking blood and molting. Each molt increases one instar, and after reaching the fifth instar, they will emerge as adults. In the adult stage, they have two pairs of wings and the ability to fly and reproduce.

Adults and nymphs of the Triatomine bug | AFPMB / Flickr

From Darwin's description, we already know that cone bug bites do not cause strong pain, which makes them more difficult to detect and more dangerous. In a dilapidated house with poor sanitary conditions, there may be hundreds of harassing cone bugs lurking in one room. At night, a person will encounter many "kissing bugs" and will not notice until he wakes up. This kind of "kiss" is not romantic, and even carries the meaning of "kiss of death". It brings a terrible infectious disease .

Trypanosoma cruzi and Chagas disease

In Darwin's time, people living in South America knew about this blood-sucking insect, but they didn't know that it was the culprit of a deadly disease. In 1909, when Brazilian doctor Carlos Chagas was studying malaria in a village in Brazil, many local patients told him that there was a bug that sucked human blood at night, which was disturbing. By understanding the distribution of this insect in human residences and his own professional sensitivity, Chagas realized that this blood-sucking insect might carry an unknown parasite that spreads diseases between people by biting and sucking blood.

Dr. Carlos Chagas | ZEISS Microscopy / Wikimedia Commons

Later studies confirmed his judgment. He found a protozoan called Trypanosoma cruzi in the body of the harassing triatomine bug, and later found the same organism in a two-year-old patient. The disease caused by Trypanosoma cruzi is named American Chagas disease , also known as Chagas disease. However, Trypanosoma cruzi is not transmitted by biting and sucking blood like mosquitoes, but by the excrement of triatomine bugs. All triatomine bugs are potential carriers of Trypanosoma cruzi, and the harassing triatomine bug has become the main carrier of Trypanosoma cruzi in the genus Triatomine because of its large number, wide distribution, and close relationship with human life.

When the harassing cone bug bites a person, it leaves behind excrement. When people scratch, they unconsciously reach out and smear the excrement of the cone bug on the bite, eyes, nose, mouth or other broken skin. At this time, Trypanosoma cruzi takes the opportunity to enter the human body. In addition, if you accidentally eat food contaminated with Trypanosoma cruzi, come into contact with the excrement of animals infected with Trypanosoma cruzi, or receive blood from patients infected with Trypanosoma cruzi, you may get Chagas disease. Pregnant women infected with Trypanosoma cruzi can directly transmit the disease to their newborns.

A sign in rural Central America promoting Chagas disease prevention | Kent MacElwee / Flickr

Chagas disease is mainly prevalent in 18 countries in Central and South America , from the southern United States to southern Argentina. Brazil, Argentina, Chile, Bolivia, Venezuela and other countries are the main epidemic areas. According to statistics from the World Health Organization, about 6 to 7 million people in the world have been infected with Trypanosoma cruzi, mainly in rural Latin America. With the population mobility brought about by globalization, the disease has also spread to cities and other areas.

Know yourself and your enemy to prevent diseases

Chagas disease is divided into acute and chronic phases . The acute phase lasts about 2 months after the initial infection, when a large number of Trypanosoma cruzi spreads in the human body through the blood circulation. Different people will have different reactions within 1-2 weeks after being bitten by a cone bug. A few people will develop erythema and nodules (called Chagas nodules). If the conjunctiva is bitten, conjunctivitis and preauricular lymphadenopathy (called Romana sign) will occur, as well as fever, headache, and difficulty breathing. A very small number of people will die from acute heart failure or acute meningitis due to complications of acute myocarditis.

Triatoma nuisance bugs in their natural environment | juanghi / inaturalist.org

In a sense, having symptoms is a good thing - people with symptoms will go to the hospital for treatment in time. The main method is to use two drugs, benzyl nitropropene and nitrofuran, to kill parasites . Except for pregnant women, people with liver and kidney dysfunction, and mental patients, everyone can use them. If the medication is used in time during the acute stage, the cure rate is very high. The younger the age and the earlier the treatment time, the greater the possibility of cure.

The trouble is that more than half of people infected with Trypanosoma cruzi are asymptomatic or have very mild symptoms. If not treated in time, after the acute phase, Chagas disease enters the next phase - the latent phase . This phase can last for weeks or months, and 50-70% of patients will subside the acute phase symptoms during this phase and will not develop the disease again.

Trypanosoma cruzi in a blood sample | CDC / Wikimedia Commons

About one-third of patients enter the most troublesome chronic phase after the latent phase. In the chronic phase, the parasites lurk in the muscles of the heart and digestive tract. Up to 30% of patients develop heart problems, and up to 10% develop digestive tract (typically an enlarged esophagus or colon), neurological, or mixed lesions. In the following years to decades, patients may die suddenly from arrhythmias or from damage to the heart muscle and its nervous system, resulting in an enlarged heart, edema, and heart failure, also known as Chagas heart disease.

Later researchers inferred that one of the causes of Darwin's death might be Chagas disease . Perhaps it was because of that bite that he was infected with Trypanosoma cruzi. After the incubation period, the chronic symptoms of Chagas disease accompanied him for the rest of his life.

Darwin: Careless | Wikimedia Commons

In 2020, the COVID-19 pandemic swept the world. The bitter lesson it brought us is to pay attention to and recognize infectious diseases in advance, and to prevent them in advance. In this era, we don’t need to take the Beagle for a long voyage. We can fly to the other hemisphere in one day. If we go to unfamiliar tropical areas, especially in Latin America and Africa, we must check the local epidemic situation in advance and avoid it in advance. If you have fever symptoms after traveling, you must pay attention to it, go to the hospital in time to inform the situation and conduct infectious disease screening.

Since there is no vaccine or medicine to prevent charas, if you go to Latin America where charas is prevalent, you should try to live in places with good sanitary conditions , avoid eating salads, uncooked vegetables, unpeeled fruits and unpasteurized juice, spray insect repellent on exposed skin, and always pay attention to bites from cone bugs and other insects.

Bed nets are a good way to prevent cone bug bites | Mx.Granger / Wikimedia Commons

In recent years, some media have called Chagas disease "the new AIDS", which is inappropriate and has increased people's unwarranted panic. In fact, China is not a major epidemic area of ​​Chagas disease, and there are very few species of cone bugs. There is no need to worry too much about being infected with Chagas disease in China.

Author: Sandie Ji

This article comes from GuokrNature (ID: GuokrNature)