Triatominos: What is a Vinchuca?

What is a vinchuca?

The natural transmission of T. Cruzi and the geographical distribution of Chagas disease are determined by some hematophogous insescts of the Reduviidae family and Triatominae sub-family.

In South America, triatominae are known by different names: “Vinchuca” (is one of the most popular); “Barbeiros” in Brazil; “Pitos” in Colombia; “Chinche besucón”, “Chipos”  “Chiramacas”, “Chinches aladas”, amongst others, depending on the region. There are more than 100 species in the New World, and there are possibly 13 species in Eurasia and Africa, which are of  little epidemiological interest.

All of the amerindia species are potential vectors although only 50% have been found to be naturally infected by Trypanosoma cruzi. Out of all of these, the most efficient vector and which frequently  colonises domestic habitats is Triatoma infestans As with all insects, the body of the vinchuca is made up of three main divisions: head, thorax and abdomen. It can be observed that the head has sensory organs, the thorax contains the locomotion appendices and  the abdomen  holds the reproductive organs and breathing system.

The head is long and fusiform as in most of the species. It has a pair of compound eyes which are globular and protruding, two ocelli, a pair of antennae, and sensory organs which have not yet been clearly defined. On the ventral surface of the thorax there are legs which are lean and relatively long. Most of the dorsal surface of the thorax is covered by wings. The conexive structure surrounding the abdomen has transversal markings which are important for the identification of vinchucas Intradomiciliary vinchuca There are more than a hundred species of vinchucas, but not all of them are important in the transmission of Trypanosoma cruzi, the microscopic unicelular parasite which is the agent of Chagas disease.

One group of species is to be found in the wild and is the vector of Trypanosoma cruzi amongst wild mammals. Another group tends to invade the peridomiciliary area and establishes itself in henhouses, farmyards and rabbit hutches etc; it feeds on domestic animals and participates in the transmission of the parasite to dogs, cats and other mammals which breed near  areas which are inhabited: this species of vinchucas lives very close to humans but does not invade areas where humans live and therefore, does not feed on them and does not transmit the disease.

 

The main species of triatominae of any significance in the transmission of Chagas disease belongs to three genres: Rhodnius, Panstrongylus and Triatoma

Genre

Species

Rhodnius

pallescens, prolixus, nasutus, neglectus

Panstrongylus

megistus, herreri

Triatoma

infestans, barberi, brasiliensis, dimidiata, maculata, pseudomaculata, phylosoma, sordida, guasayana

Geographical distribution.

Areas at risk of  vectorial transmission of Chagas disease and species which are significant in the transmission.

Without any doubt, the most significant species in the transmission is Triatoma infestans, more commonly known as black vinchuca or simply, vinchuca.

An adult is between 2.5 and 3 cms long; the male is not as long as the female. A fairly safe way to distinguish indoor vinchucas from other species is to observe the bases of the legs which are yellow and stand out from the overall black colour of the insect.

It is born from an egg. The female can lay up to 200 eliptical eggs of a white colour when just laid. This colour becomes more pinky as the embrion develops. Depending on temperature the process is completed in 20 – 50 days. Eggs are laid in soil, in wall cracks and other places which may be more or less hidden.

From the moment it abandons the egg until it becomes an adult the insect goes through a series of transformations (metamorphosis) with a variable duration depending on temperature, humidity and feedin.

At birth, the insect is 3 mm long and looks like an adult but lacks wings. At this first phase of  metamorphosis it is known as “chinche pila”. Several weeks later, the nymph molts and increases its size but still lacks wings. These molts take place five times: each time the nymph becomes larger. Wings appear after the last molt and the insect acquires its final aspect.

All this process lasts about 7 months under optimum conditions: the life span of the adult insect is of about fifteen months.

Biology

The vinchuca - Triatoma infestans, Klug, 1834 (Hemiptera: Triatomidae)- is an exclusively indoor species. It is mainly to be found where humans live and also in places where domestic animals live – henhouses, pigeon lofts and rabbit hatches.

Not all human living spaces are suitable for vinchucas to nest. They tend to choose places with special characteristics which favour their habits: the insect takes refuge in cracks in floors or walls, behind furniture or other objects, places which are not usually cleaned, underneath the cover of the ceilings or walls. Storage areas where things are not often moved are also much favoured places.

Indoors, the presence of vinchuca is not hard to discover due to its excretions, of a yellowish brown and black colour which that they stain the walls as if they were drops of Chinese ink.

On warm or mild nights , when people go to bed and turn out lights the vinchucas  start to come out of their hiding places; if they are in the roofs or at the top of walls they drop making a characteristic give away sound.  Vinchucas only  feed at night and during daylight they will not leave their hiding places. This habit explains why many people in the most affected areas sleep with lights on in order to scare off  these insects.

Once on its victim, whether it be man or animal, and immobile whilst resting, the vinchuca it straightens its tip, that it normally takes to fold on the part inferior of the head, supports its end in the skin, introduces its long stings, it injects irritating and anticoagulating saliva and it begins to absorb blood during some minutes. The bite does not produce any discomfort at all, so the the insect can feed peacefully and then leave without being noticed in most cases.

After the puncture, the affected region usually presents/displays a slight reddish swelling that produces irritation, sometimes is made something painful but soon it passes without majors consequences. Once full of blood, the vinchuca looks something like a grape, it cannot fly and returns to its hiding place by crawling along the floor and then up the wall. It needs to rest frequently and can take many minutes and even hours.

The resistance of vinchucas to fasting is remarkable: a first stage nymph can live for up to three months without needing to feed; the maximum resistance which has been observed is of a fifth stage nymph which can  endure up to  200 days without feeding.

 

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