A perfect home for humans, bugs and trypanosomes alike

In microbiology we discussed Chagas disease, an illness caused by Tryptopanosoma cruzi transmitted to the host (indirectly) via the reduviid, ‘Kissing Bug.’ Chagas disease is relatively common in parts of South and Central America inhabited by people living in thatched-roof huts. These living conditions provide just the right environment for the three species, human, insect and trypanosome, to co-exist.

A reduviid

T. cruzi depends upon Kissing bugs to act as vectors. The insect host, kissing bug, lives in the thatch roofs of homes. During the night, it descends into the living space and feeds on human hosts’ soft tissue around the mouth and eyes. As it does so, it defecates close to the feeding site. When the human scratches as the bite, they unwittingly drag feces into the wound. Once inside, the trypanosome finds a cell to infect and begin life in its second host.

Two forms of the microbe live in the insect, the epimastigote, which reproduces in the hindgut then transforms into a trypomastigote that passes from the insect into the mammalian host. Once in a mammal, the trypomastigote will find an appropriate cell to infect (typically muscle, epithelial of phagocytic cells), transform itself into the amastigote stage and replicate in this host’s cells. Once the cell is filled with amastigotes, they will transform once more into the highly active, mobile trypomastigote stage which breaks out of the cell and either infect new cells or return to the reduviid through a blood feeding.

T. cruzi forms during different stages of its life in insect and mammalian hosts

This video, from videosINBEB, shows how the organism passes from host to host:

Replication in mammalian (human) cells occurs with the intracellular amastigote phase, seen here filling the cytoplasm of a fibroblast.

The Reduviidiae family of insects include species found throughout the Americas, although these tend to be different species living in different locations. However, a recent Scientific American article suggests that Chagas Disease may make  inroads into the southern United States, despite the different host conditions.

North America has so far been spared from this plague for a number of reasons: The 11 species of kissing bugs endemic to the U.S. South and Southwest tend to defecateafter leaving their unwitting hosts, reducing the likelihood of spreading the parasite …[Further, the]  thatched roofs [that] make perfect hideouts for the pests, [are] not typical of U.S. homes.

How far Chagas Disease will spread is highly speculative. While immigrants from South America may carry Chagas Disease north and some insects have been found carrying both human DNA and T. cruzi, few cases of vector-transmitted disease have been documented.

References

1. “Diagnosis and Treatment of Myocarditis”,  edited by José Milei and Giuseppe Ambrosio, Published: May 8, 2013 Chapter 5 “Pathogenesis of Chronic Chagasic Myocarditis” By Julián González, Francisco Azzato, Giusepe Ambrosio and José Milei under CC BY 3.0 license

2. “Bugs That Transmit “Silent Killer” Are Biting More in the U.S.” Scientific American. Apr 9, 2012 |By Rachel Nuwer