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Emerging viruses and the “me too” of a ubiquitous trypanosome

One of the tasks most demanded of today's biologists (and sometimes also part of their technological dreams) is to quickly identify a new microorganism and give it a precise taxonomic status. In our current surfeit of molecular methods and sophisticated instruments this seems to be a simple task, such as one might assign to undergraduate students as home work for the next lab class. This is the perfect world advertised by manufacturers of the myriad of devices and kits that promise an unequivocal identification for any microorganism. However the scientific literature reveals a more complex picture which is not as simple as the typical newcomers would think. The re-descriptions of species, new methods for building taxonomic trees, alternative clustering schemes and the assignment of newly discovered organisms to incertae sedis are not the “exception to the rule”. Most astonishingly: according to a biodiversity estimate (Mora et al. 2011), less than 14% of all living species in the earth has been so far described. This might be an exciting scientific challenge, but it may also be a cloudy scenario for public health policy-makers because we cannot control (or fight efficiently) what we do not know in detail. In June 2015 [110(4)] issue of Memórias do Instituto Oswaldo Cruz, two papers contribute to reinforce these ideas: the detection of Zyka virus in Brazil (Zanluca et al. 2015) and the biochemical similarity of Trypanosoma brucei and Trypanosoma evansi (Moreno & Nava 2015).

Zyka is considered an emerging virus, sharing the same vector species, the Aedes aegypti mosquito, with dengue and Chikungunya viruses. The report of autochthonous transmission in Brazil (Zanluca et al. 2015) represents a real threat to the public health system of a country already suffering from dengue epidemics and other “traditional” infectious diseases. This threat notwithstanding, it might represent an opportunity to study the interplay of infectious agents and human displacements in these times of instantaneous communication, fast transport and global environmental changes. Most of time the apocalyptic scenarios portrayed by specialists in several fields have not been confirmed. The obvious question to ask is: did they not happen because we have been warned with anticipation or were they simply wrong? A tough question!

For some organisms, some questions appear to be settled a long time ago. For the protozoan parasites in the family Trypanosomatidae, in particular the genus Trypanosoma, researchers established more than a century ago their classification based on phenotypic features: morphology and behaviour in vertebrate and invertebrate hosts (and sometimes the clinical features for those infecting humans) (Hoare 1972). The trypanosomes species described so far appear to be valid and we need only to describe new discoveries (and nobody knows how many species are waiting to be described!). However for some African trypanosomes problems have arisen. Some years ago, a paper in the Proceedings of the National Academy of Sciences of the United States of America (Lai et al. 2008) reported the large degree of genetic similarity among the T. brucei species complex and their relatives T. evansi and Trypanosoma equiperdum. They concluded that T. evansi is a petit mutant of T. brucei. Now, new biochemical data published here in the Memórias do Instituto Oswaldo Cruz cast more light on this question: the activity of enzymes of central metabolism in T. brucei brucei and T. evansi are the same (Moreno & Nava 2015). Do these species deserve a reversal of their taxonomic split? Some authors argue against it (Desquesnes et al. 2013).

In times of biodiversity appraisal, the simplicity of describing a group of related organisms by a single taxonomic entry is appealing, but there remains a question formulated four centuries ago by William Shakespeare in his tragedy “Romeo and Juliet” (en.wikipedia.org/wiki/A_rose_by_any_other_name_would_smell_as_sweet): “What's in a name? That which we call a rose by any other name would smell as sweet.”

 

Adeilton Alves Brandão | Editor

REFERENCES

Desquesnes M, Holzmuller P, Lai DH, Dargantes A, Lun ZR, Jittaplapong S 2013. Trypanosoma evansi and surra: a review and perspectives on origin, history, distribution, taxonomy, morphology, hosts and pathogenic effects. BioMed Research International doi: 10.1155/2013/194176.

Hoare CA 1972. The trypanosomes of mammals. A zoological monograph, Blackwell Scientific Publications, Oxford, 749 pp.

Lai DH, Hashimi H, Lun ZR, Ayala FJ, Lukes J 2008. Adaptations of Trypanosoma brucei to gradual loss of kinetoplast DNA: Trypanosoma equiperdum and Trypanosoma evansi are petite mutants of T. brucei. Proc Natl Acad Sci USA 105: 1999-2004.

Mora C, Tittensor DP, Adl S, Simpson AGB, Worm B 2011. How many species are there on earth and in the ocean? PLoS Biol 9: e1001127.

Moreno SA, Nava M 2015. Trypanosoma evansi is alike to Trypanosoma brucei brucei in the subcellular localisation of glycolytic enzymes. Mem Inst Oswaldo Cruz 110: 468-475.

Zanluca C, de Melo VCA, Mosimann ALP, dos Santos GIV, dos Santos CND, Luz K 2015. First report of autochthonous transmission of Zika virus in Brazil. Mem Inst Oswaldo Cruz 110: 569-572.

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