Rhodnius Nasutus

''Rhodnius nasutus''

''Rhodnius nasutus'' is a Chagas disease vector native to the northeast of Brazil. It belongs to the family Reduviidae and subfamily Triatominae, which are commonly known as kissing bugs or assassin bugs. They are considered a highly important species concerning the infectious Chagas disease as they carry a parasite called Trypanosoma cruzi, that can be transmitted to the blood of mammals, including humans. This disease is an important issue in Brazil and central America due to the large number of ''Rhodnius'' species inhabiting these areas, however in recent efforts to reduce human infection, multiple variations of pesticides have dramatically reduced Triatomine populations. Therefore, the understanding and knowledge of ''Rhodnius nasutus'' greatly benefits our efforts in reducing life threatening infections.

Identification

''R. nasutus'' species are known for their chromatic pattern and range from red to chestnut-colored. These color differences have been hypothesized in many studies to correlate with the species of palm that the insect inhabits. Connection to the coloration of ''R. nasutus'' and the colors found on the stems and frond bases of the inhabited palm tree suggests a way of camouflage.

Systematics

It is important to note that the ''Rhodnius'' species are especially hard to decipher from one another as they are morphologically similar, thus taxonomy has been controversial regarding their independence. Accurately identifying ''R. nasutus'' from other species with common features plays an important role in reducing human contact with these vectors. Random amplification of polymorphic DNA (RAPD) can identify taxonomic relationships on a molecular level providing valid phylogenetic evidence on speciation. The continuation of this practice is essential for following disease transmission dynamics.

Distribution

Genetic Phylogeography

Using mitochondrial DNA sequence analysis, ''R. nasutus'' has been dated 66 thousand years, giving rise to stable populations during the Pleistocene-Holocene epochs. This time frame is consistent with the climate change event that took place in South America which marked the end of a major drought and dry season.

Geographical Range

''R. nasutus'' is predominantly found in the caatinga biome of Northeast Brazil, although due to increased deforestation and environmental damage the insect has expanded its geographic range and habitat. The species is primarily associated with the Copernicia prunifera palm tree (Carnaúba) in this area, however more recently they have been found colonizing suburban areas such as Jaguaruana, Ceará, and infesting various other palms including Licania rigida (Oiticica). The allocation of chemical measures in rural areas have pushed these insects to colonize closer to localities and urban districts. Migration into central areas of Brazil pose a threat to humans as it increases the risk of contracting Chagas disease.

Habitat

When compared to other species of the genera, ''R. nasutus'' is found to thrive better in dryer and warmer conditions. Palms located in semi-arid, higher-altitude environments inhabit greater populations compared to palms located in lower elevations where flooding occurs during rainy seasons.

The insect is found predominantly in the crowns of palm trees, they burrow their bodies into the auxiliary nodes and foliar sheaths of palms, which act as a barrier to protect them from environmental and predatory threats.

More recently, ''R. nasutus'' has been found infesting homes and farm buildings, including corrals and coops.

Human Intervention

Chemical Controls

In efforts to inhibit human contraction of diseases harbored by ''R. nasutus'', preventative measures such as chemical controls (insecticides) are distributed to high density Triatomine areas, including human dwellings. Although, the continuous re-infestation of homes that had been treated with insecticides presents the need for further research in controlling populations.

History of Chemical Control

The first insecticide used in Brazil to reduce infestations was a synthetic DDT formulation which was later found to have negative impacts on the environment. In 1970, a lindane and dieldrin compound insecticide was used until a safer organophosphorus and carbamate insecticide was formulated in the 1980's. This insecticide however, emitted a strong odor and stained walls of houses undergoing extermination. The favored and most recent insecticide used on ''R. nasutus'' is a pyrethroid formula, although the evolution of insecticide resistance has been documented in some Triatomine species.

Biological Controls

Biological controls such as the " Mark-Release-Recapture" (MRR) method, involving the placement and evaluation of trace elements in ''R. nasutus,'' allows for long-lasting molecular marking under natural conditions. This method aims to identify host-seeking behaviors of the insect by tracking migration and population dispersion. Understanding the movement of these insect vectors provides important information regarding medical insights and preventative measures towards the transmission of Chagas disease. Other biological controls such as dusting and physically marking the insect are not as effective as growing nymphs will eventually shed the marked cuticle.

Diet and feeding

Diet

''R. nasutus'' is a hematophagous insect and will feed on bloodmeal through all life stages. Their main hosts are birds and mammals, however there is evidence that these insects will find invertebrates hosts and feed on hemolymph.

Feeding Behaviour

Compared to other ''Rhondius'' species, ''R. nasutus'' displays a slower feeding time around 15-20 minutes before full engorgement. They are solenophagous insects so in order to feed they must find a suitable blood vessel in their host. During the probing period, the maxillae that is pierced into the hosts skin contract in rapid whip-like movements until a blood vessel is detected from which they can feed on. During feeding the cibarial pump, which is connected to strong muscles in the head, regulate the suction and volume intake of bloodmeal through the proboscis. Saliva plays an important role in the probing period to find blood, as well as the feeding period to regulate the flow of blood via the proboscis. ''R. nasutus'' has adapted highly efficient salivary glands which reduces the time is takes for them to find blood vessels.

Transmission of ''T. cruzi''

Feeding done by ''R. nasutus'' is one of the leading causes of ''T. cuzi'' parasites being transmitted to mammals, which leads to Chagas disease. ''T. cruzi'' is found in the fecal matter of infected ''R. nasutus'' and is transmitted to mammals through the blood stream. While feeding or immediately after feeding, the vector insect will defecate on their host near the pierced skin. If the host disrupts the fecal matter by scratching or any other means of moving the feces around, ''T. cruzi'' will be able to get in through the pierced skin where it then spreads disease throughout the bloodstream.

External sources

This video shows how the transmission of harmful diseases via ''T. cruzi'' is not limited to Latin America and Brazil, but has made its way through other ''Rhodnius'' species posing threats to Americans in Tennessee, US.


This video establishes in more detail how ''T. cruzi'' gets into the bloodstream and how Chagas disease affects the body.

References

{{Taxonbar, from=Q7321098

Reduviidae
Insects described in 1859
Hemiptera of South America