ARTIGO DE REVISÃO | REVIEW ARTICLE | ARTÍCULO DE REVISIÓN

 

Leishmania chagasi Cunha & Chagas, 1937: indigenous or introduced? A brief review

 

Leishmania chagasi Cunha & Chagas, 1937: nativa ou introduzida? Uma breve revisão

 

Leishmania chagasi Cunha & Chagas, 1937: ¿nativa o introducida? Una breve revisión

 

 

Fernando Tobias Silveira^I; Carlos Eduardo Pereira Corbett^II

^ISeção de Parasitologia, Instituto Evandro Chagas/SVS/MS, Ananindeua, Pará, Brasil. Núcleo de Medicina Tropical, Universidade Federal do Pará, Belém, Pará, Brasil
^IIDepartamento de Patologia, Faculdade de Medicina da Universidade de São Paulo, São Paulo, São Paulo, Brasil

Correspondence
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ABSTRACT

This review focused on the etiology of American visceral leishmaniasis due to a recent polemic regarding the origin of its etiological agent, Leishmania chagasi Cunha & Chagas, 1937. This parasite was described as a new Leishmania species in light of its inability to produce experimentally visceral disease in domestic dogs; this characteristic distinguished it from the other prior known etiologic agent of visceral leishmaniasis in the Mediterranean Basin of Europe, Leishmania infantum Nicolle, 1908. After 50 years of Leishmania chagasi investigation, the genus Leishmania was reviewed and the parasite was reclassified as a member of the subgenus Leishmania, species Leishmania (Leishmania) chagasi. Recently, after molecular analysis using the random amplified polymorphic DNA (RAPD) technique that compared L. (L.) chagasi with L. (L.) infantum, it was concluded that these species were genetically indistinguishable and, therefore, L. (L.) chagasi was regarded as synonymous with L. (L.) infantum. For this reason, this review has evaluated all knowledge concerning the eco-epidemiology of L. (L.) chagasi in the Brazilian Amazon, principally in regard to the sylvatic habits of its phlebotomine sandfly vector, Lutzomyia longipalpis, and its vertebrate reservoir, the wild fox Cerdocyon thous, with the aim of showing that L. (L.) chagasi cannot be neglected from the parasitological investigation of visceral leishmaniasis in the New World; it must be considered, at least, at the subspecific level as Leishmania (L.) infantum chagasi.

Keywords: Leishmania; Leishmaniasis, Visceral; Leishmania chagasi.

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RESUMO

Esta revisão aborda a etiologia da leishmaniose visceral americana devido a uma recente polêmica sobre a origem do seu agente etiológico, a Leishmania chagasi Cunha & Chagas, 1937. Conforme é sabido, este parasito foi descrito como uma nova espécie de Leishmania em razão da sua incapacidade de produzir, experimentalmente, a leishmaniose visceral no cão doméstico; este caráter a diferenciou de outro agente etiológico já conhecido da leishmaniose visceral na Bacia do Mediterrâneo na Europa: Leishmania infantum Nicolle, 1908. Após 50 anos da descrição da Leishmania chagasi, o gênero Leishmania sofreu ampla revisão e o parasito foi reclassificado como um membro do subgênero Leishmania, espécie Leishmania (Leishmania) chagasi. Recentemente, em seguida a uma análise molecular usando a técnica da amplificação aleatória polimórfica do DNA (RAPD), que comparou a L. (L.) chagasi com a L. (L.) infantum, foi concluído que ambos os parasitos eram geneticamente indistinguíveis e, portanto, que a L. (L.) chagasi era sinônimo de L. (L.) infantum. Por esse motivo, esta revisão procurou agregar todo o conhecimento sobre a eco-epidemiologia da L. (L.) chagasi na Amazônia brasileira, principalmente acerca dos hábitos silvestres de seu flebotomíneo vetor, Lutzomyia longipalis, e seu reservatório vertebrado, a raposa do campo Cerdocyon thous, com o propósito de demonstrar que a L. (L.) chagasi não pode ser negligenciada do cenário parasitológico da leishmaniose visceral no Novo Mundo; ela deve ser considerada, pelo menos em um nível subespecífico, como Leishmania (L.) infantum chagasi.

Palavras-chave: Leishmania; Leishmaniose Visceral; Leishmania chagasi.

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RESUMEN

Esta revisión aborda la etiología de la leishmaniasis visceral americana debido a una reciente polémica sobre el origen de su agente etiológico, la Leishmania chagasi Cunha & Chagas, 1937. Como se sabe, este parásito fue destrito como una nueva especie de Leishmania en razón de su incapacidad de producir, experimentalmente, la leishmaniasis visceral en el perro doméstico; este carácter la diferenció de otro agente etiológico ya conocido de leishmaniasis visceral en la Cuenca del Mediterráneo en Europa: Leishmania infantum Nicolle, 1908. Luego de 50 años de la descripción de la Leishmania chagasi, el género Leishmania ha sufrido amplia revisión y el parásito fue reclasificado como un miembro del subgénero Leishmania, especie Leishmania (Leishmania) chagasi. Recientemente, en seguida a un análisis molecular usando la técnica de amplificación aleatoria polimórfica del DNA (RAPD), que comparó L. (L.) chagasi con L. (L.) infantum, se concluye que ambos parásitos eran genéticamente indistinguibles y, por lo tanto, que L. (L.) chagasi era sinónimo de L. (L.) infantum. Por ese motivo, esta revisión buscó agregar todo el conocimiento sobre la ecoepidemiología de L. (L.) chagasi en la Amazonía brasileña, principalmente acerca de los hábitos silvestres de su flebótomo vector, Lutzomyia longipalis, y su reservorio vertebrado, el zorro de campo Cerdocyon thous, con el propósito de demostrar que no se debe ser negligente con L. (L.) chagasi en el escenario parasitológico de la leishmaniasis visceral en el Nuevo Mundo; debe ser considerada, al menos en un nivel subespecífico, como Leishmania (L.) infantum chagasi.

Palabras clave: Leishmania; Leishmaniasis Visceral; Leishmania chagasi.

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HISTORICAL BACKGROUND ON THE TAXONOMIC STATUS OF THE ETIOLOGIC AGENT OF AMERICAN VISCERAL LEISHMANIASIS

The etiologic agent of American visceral leishmaniasis (AVL) was first described by Cunha and Chagas³ with the specific name of Leishmania chagasi, a protozoal parasite that belongs to the family Trypanosomatidae Doflein, 1901 emended Grobben, 1905 and the genus Leishmania Ross, 1903. The decision to regard it as a new Leishmania species was principally due to the repeated negative results that followed from attempts to experimentally infect dogs with the parasite, which distinguished it from the other previously known etiologic agent of visceral leishmaniasis in some European countries of the Mediterranean Basin, Leishmania infantum Nicolle, 1908. However, only 50 years after the description of Leishmania chagasi, Lainson and Shaw¹⁰ performed a wide review of the genus Leishmania and reclassified the parasite as a member of the subgenus Leishmania Saf'Janova, 1982 (= Ross, 1903), species Leishmania (Leishmania) chagasi.

Recently, after a large comparison of several strains of L. (L.) chagasi that have been isolated from different origins and countries in South America, especially in Brazil (from humans, domestic dogs, and the wild fox Cerdocyon thous), and of strains of L. (L.) infantum that originated from the endemic area of visceral leishmaniasis in some countries from the Mediterranean Basin in Europe, such as Portugal and Spain, the random amplified polymorphic DNA (RAPD) technique illustrated that the DNA sequences of both species of parasites were identical. For this reason, the authors of this analysis concluded that L. (L.) chagasi is synonymous with L. (L.) infantum and therefore proposed that L. (L.) chagasi should not be considered as a valid species¹⁵.

More recently, however, Lainson and Shaw¹¹ defended the maintenance of the parasitological entity at the subspecific level as Leishmania (L.) infantum chagasi based on its ecological characteristics, such as the sylvatic habitat of its phlebotomine sandfly vector, Lutzomyia longipalpis⁷, and its natural vertebrate reservoir, the wild fox Cerdocyon thous²⁰, in addition to previously established distinct differences between the kDNA fragment profiles of L. (L.) chagasi and L. (L.) infantum demonstrated by the use of a restriction endonuclease digestion technique^6,5, radioiodinated surface proteins of their promastigotes, monoclonal antibodies generated against promastigote surfaces¹⁸, and comparative radiorespirometry studies⁴.

 

THE CURRENT DILEMMA ON THE ORIGIN OF LEISHMANIA CHAGASI: IS IT INDIGENOUS OR INTRODUCED?

Despite the reasonable argument presented by Lainson and Shaw¹¹ that aimed to maintain the scientific name L. (L.) i. chagasi at the subspecific level, which appears absolutely justifiable in view of the long scientific history built on more than 50 years of published works on the eco-epidemiology, clinical manifestations and immunopathology of the disease caused by this parasite in America, some authors^15,16,14 have made attempts to disqualify any effort towards the maintenance of the parasitological entity either at the specific level [L. (L.) chagasi Lainson & Shaw, 1987] or at the subspecific level [L. (L.) i. chagasi Lainson & Shaw, 2005]. For these authors, only L. (L.) infantum and L. (L.) donovani are recognized as etiologic agents of visceral leishmaniasis, with the former occurring in the endemic areas of the Mediterranean Basin in Europe, North Africa and Central and South America and the latter in the endemic areas of India, East-Africa and the Middle East.

Taking this issue into account, we consider opportune to express our opinion concerning the taxonomic proposal by Mauricio et al^15,16, who used DNA molecular analysis of the parasite as the unique and definitive criterion for deciding the originality of Leishmania species under study. Furthermore, it should also be stressed that a species definition might not only be based on its phylogenetic background but also on its biological, phenetic and phenotypic characteristics that are the result of the parasite-genomic background and environment interactions. Thus, modern genetic concepts and technologies should be used to utilize these concepts²⁴. In this respect, it appears clear that Mauricio et al^15,16 have neglected the phenotypic features that are typically used for classifying Leishmania parasites, such as the following: the morphology of amastigote and promastigote forms; the experimental biological behavior of the parasite in domestic and wild animals and in the phlebotomine sandfly vectors; and immunology, biochemistry, eco-epidemiology and pathogeny, i.e., the clinical manifestations of infection^10,19.

In contradiction to these authors^15,16,14 who asserted that L. (L.) chagasi (synonymous with L. (L.) infantum) was introduced in America during its colonization, two issues must be addressed before any affirmation. First, considering that the first AVL cases in Brazil were diagnosed in 1934¹⁷, how to explain that in a small time interval, little more than 400 years after colonization, L. (L.) infantum was promptly capable of surviving in Cerdocyon thous, which, differently from domestic dog, does not develop any signals or symptoms due to a pathogenic action induced by the parasite. This type of adaptation reflects a stage of coexistence between the parasite and the vertebrate host, which is generally accepted only after a long interactive process between the parasite and the immune response of the vertebrate host that occurs over thousands of years. Second, L. (L.) infantum, which was well adapted to its phlebotomine sandfly vector, Phlebotomus dubosqi, in endemic countries in Europe, would have needed to promptly adapt to another species of phlebotomine sandfly vector, Lutzomyia longipalpis, from a continent that presents completely different weather and ecology from those in Europe. Additionally, it is also important to emphasize recent evidence suggesting that this speciation process between the parasite and its phlebotomine sandfly vector is strongly influenced by a specific interaction between the ligand glycoconjugate molecules, principally lipophosphoglycan (LPG), present on the plasmatic membrane surface of the metacyclic promastigote forms of Leishmania species and their receptors on the epithelial cell membrane of the midgut wall of the phlebotomine sandfly vector^2,22,21. LPG has been implicated as a specific adhesion molecule that mediates the interaction of Leishmania with the midgut epithelium of the phlebotomine sandfly vector. Thus, it might be expected that L. (L.) infantum, which is naturally transmitted by Phlebotomus dubosqi, would promptly be capable of adapting to the midgut epithelium of Lutzomyia longipalpis, a phlebotomine sandfly vector for a completely different species and genus of L. (L.) infantum in an endemic area in Europe.

As previously established, this speciation process among the parasite, its biological vector and its wild reservoir, which characterizes a natural enzootic cycle of Leishmania species, was strongly supported in the case of a Leishmania parasite that is very closely related to that L. (L.) chagasi that was isolated from the viscera (liver and spleen) of three healthy Cerdocyon thous wild foxes that were captured in a forested peri-urban area called "Utinga Environmental Park" (Figure 1), near Belém, the capital city of Pará State, Brazilian Amazon, where there is no evidence of human or canine visceral disease to date. However, this Leishmania parasite has proved to cause lethal visceralizing infection in golden hamsters after three months of intraperitoneal inoculation¹². Thus, considering that this area is still uninhabited by humans and dogs, this finding represents a strong evidence on the existence of an indigenous enzootic cycle of L. (L.) chagasi-like parasites in the Brazilian Amazon, which was certainly originated much before the recent history of America colonization.

 

 

Another point that contradicts the evolutionary hypothesis^15,16,14, which agrees that the genus Leishmania originated in South America in the Paleocene or Eocene with subsequent diversification after migration into Asia, concerns the interpretation on what has occurred with the ancestral Leishmania that migrated to Asia. The evolutionary hypothesis asserts that no ancestral Leishmania remained in South America, however, how to explain the origin of a large number of Leishmania species existing in this region; actually, there are more than 20 well-recognized Leishmania species belonging to subgenera Leishmania and Viannia, including L. (L.) chagasi, the only leishmanial parasite responsible for AVL¹¹.

 

CONCLUDING REMARKS

Considering the aforementioned aspects, two major features should be addressed. The first feature refers to the considerable speculation over the evolutionary hypothesis proposed by Lukes et al¹⁴ based on the phylogenetic analysis between L. (L.) chagasi and L. (L.) infantum. As we have commented, although a great phylogenetic similarity between these two parasites has been demonstrated, it was proposed by these authors that the genus Leishmania originated in South America in the Paleocene or Eocene with subsequent diversification after its migration into Asia. This yielded two main branches: Leishmania donovani, in the Indian subcontinent, and Leishmania infantum, in Europe. More recently, it was also suggested that Leishmania infantum would have been introduced in America by settlers. This evolutionary hypothesis appears both speculative and contradictory; it is impossible to believe that a Leishmania ancestor would migrate into Asia without leaving in its original birth place a descending parasite. Recently, in the Utinga Environmental Park, the same area where Lainson et al¹² found a L. (L.) chagasi-like parasite from natural visceral-infection in Cerdocyon thous, a Leishmania parasite was identified in Lutzomyia tuberculata, Leishmania (Viannia) utingensis Braga, Lainson, Ishikawa & Shaw¹. This parasite has never been found out of the local-type where it was firstly isolated, clearly demonstrating, together with L. (L.) chagasi-like parasites, the existence of closed indigenous enzootic cycles of Leishmania parasites in the New World that undoubtedly have directly descended from an indigenous Leishmania ancestor. In accordance with this finding, it should also been emphasized the recent finding of Lutzomyia longipalpis in a forested area in the Instituto Evandro Chagas field in Ananindeua Municipality, Pará State, Brazil²³, which is contiguous with the Utinga Environmental Park. This further confirms the existence of an indigenous enzootic cycle of L. (L.) chagasi in this area where there is no evidence of human or canine visceral disease.

The second feature to be addressed is the criteria (morphology, experimental biology, eco-epidemiology, immunology, biochemistry, and pathogenicity) used for identification and classification of Leishmania parasites, which were largely discussed by Lainson and Shaw¹⁰ in the last review of the genus Leishmania. As it was recently observed by Tibayrenc²⁴, although the great advantages of Leishmania-DNA analysis by molecular biology techniques for different aims have been acknowledged, DNA analysis should be used as a complementary tool for the precise identification of a Leishmania species and not as the determining factor for its identification. This way, we cannot omit the importance of some works regarding, principally, the originality of the biology and eco-epidemiology of L. (L.) chagasi in America^{7,20,12,13,9,8}.

In conclusion, we cannot agree with the proposal of disqualifying L. (L.) chagasi, which has been recognized for over 50 years as the etiologic agent of AVL, in view of its DNA similarity to L. (L.) infantum. This finding alone does not confirm its taxonomic characteristics sufficiently enough to negate all scientific knowledge that has been accumulated concerning this Leishmania parasite in the last 50 years. Thus, we believe the best decision to be made regarding this issue is to maintain the subspecific status of the etiologic agent of AVL as L. (L.) i. chagasi, as it was proposed by Lainson and Shaw¹¹ in their last review of the neotropical Leishmania parasites with medical importance.

 

REFERENCES

1 Braga RR, Lainson R, Ishikawa EA, Shaw JJ. Leishmania (Viannia) utingensis n. sp., a parasite from the sandfly Lutzomyia (Viannamyia) tuberculata in Amazonian Brazil. Parasite. 2003 Jun;10(2):111-8.         [ Links ]

2 Butcher BA, Turco SJ, Hilty BA, Pimenta PF, Panunzio M, Sacks DL. Deficiency in β1,3-galactosyltransferase of a Leishmania major lipophosphoglycan mutant adversely influences the Leishmania-sand fly interaction. J Biol Chem. 1996 Aug;271(34):20573-9.         [ Links ]

3 Cunha AM, Chagas E. Nova espécie de protozoário do gênero Leishmania patogênico para o homem. Leishmania chagasi n.sp. Nota prévia. Hospital (Rio J) 1937;11:3-9.

4 Decker-Jackson FE, Tang DB. Identification of Leishmania spp. by radiorespirometry: II. A statistical method of data analysis to evaluate the reproductibility and sensitivity of the technique. In: Chance ML, Walton BC, editors. Biochemical Characterization of Leishmania. Geneva: Pan American Health Organization; 1982. p. 205-45.

5 Jackson PR, Stiteler JM, Wohlieter JA, Reed SG, Badaró R, Inverso JA, et al. Characterization of Leishmania responsible for visceral disease in Brazil by restriction endonuclease digestion and hybridization of kinetoplastic DNA. In: 11th Congress International Tropical Medicine and Malaria, Calgary, Canada; 1984. p. 68.

6 Jackson PR, Wohlieter JA, Hockmeyer WT. Leishmania characterization by restriction endonuclease digestion of kinetoplastic DNA. 5th Congress International Parasitology, Toronto, Canada; 1982. p. 342.

7 Lainson R, Dye C, Shaw JJ, MacDonald DW, Courtenay O, Souza AAA, et al. Amazonian visceral leishmaniasis - distribution of the vector Lutzomyia longipalpis (Lutz & Neiva) in relation to the fox Cerdocyon thous (Linn.) and the efficiency of this reservoir host as a source of infection. Mem Inst Oswaldo Cruz. 1990 Jan-Mar;85(1):135-7. Doi:10.1590/S0074-02761990000100027         [ Links ]

8 Lainson R, Ishikawa EA, Silveira FT. American visceral leishmaniasis: wild animal hosts. Trans Roy Soc Trop Med Hyg. 2002 Nov-Dec;96:(6)30-1.         [ Links ]

9 Lainson R, Shaw JJ. A brief history of the genus Leishmania (Protozoa: Kinetoplastida) in the Americas with particular reference to Amazonian Brazil. Cienc Cult. 1992 Mar-Abr;44(2-3):94-106.         [ Links ]

10 Lainson R, Shaw JJ. Evolution, classification and geographical distribution. In: Peteers W, Killick-Kendrick R, editors. The Leishmaniasis in Biology and Medicine. London: Press Inc; 1987. p. 12-120.

11 Lainson R, Shaw JJ. Leishmaniasis in the new world. In: Collier L, Balows A, Sussman M, editors. Topley & Wilson's Microbiology and Microbial Infections, 10th ed. London: E Arnold; 2005. p. 313-49.

12 Lainson R, Shaw JJ, Lins ZC. Leishmaniasis in Brazil: IV The fox, Cerdocyon thous (L) as a reservoir of Leishmania donovani in Para State, Brazil. Trans R Soc Trop Med Hyg. 1969;63(6):741-5.         [ Links ]

13 Lainson R, Shaw JJ, Silveira FT, Braga RR. American visceral leishmaniasis: on the origin of Leishmania (Leishmania) chagasi. Trans R Soc Trop Med Hyg. 1987; 81(3):517.

14 Lukes J, Maurício IL, Schönian G, Dujardin JC, Soteriadou K, Dedet JP, et al. Evolutionary and geographical history of the Leishmania donovani complex with a revision of current taxonomy. Proc Natl Acad Sci U S A. 2007 May;104(22):9375-80.         [ Links ]

15 Mauricio IL, Howard MK, Stothard JR, Miles MA. Genomic diversity in the Leishmania donovani complex. Parasitology. 1999 Sep;119(Pt 3):237-46. Doi:10.1017/S0031182099004710         [ Links ]

16 Mauricio IL, Stothard JR, Miles MA. The strange case of Leishmania chagasi. Parasitol Today. 2000 May;16(5):188-9.

17 Penna HA. Leishmaniose visceral no Brasil. Bras Med. 1934;48:949-50.

18 Santoro F, Lemesre JL, Rizvi FS, Afchain D, Sadogirsky M. Spécificité au niveau de proteins de surface des promastigotas de Leishmania donovani (Laveran et Mesnil, 1903), Leishmania infantum Nicolle, 1908 et Leishmania chagasi Cunha et Chagas, 1937. In: Rioux JA, editor. Leishmania. Taxonomie et Phylogenese. Applications Éco-Épidémiologiques. Colloque International; 1984 July 2-6; Montpellier: L'Institut Méditerranéen d'Études Épidémiologiques et Écologiques; 1986. p. 71-6.

19 Silveira FT, Ishikawa EA, Souza AAA, Lainson R. An outbreak of cutaneous leishmaniasis among soldiers in Belém, Pará State, Brazil, caused by Leishmania (Viannia) lindenbergi n. sp. A new leishmanial parasite of  man  in  the Amazon  region. Parasite. 2002 Mar;9(1):43-50.         [ Links ]

20 Silveira FT, Lainson R, Shaw JJ, Póvoa MM. Leishmaniasis in Brazil: XVIII. Further evidence incriminating the fox Cerdocyon thous (L) as a reservoir of Amazonian visceral leshmaniasis. Trans Roy Soc Trop Med Hyg. 1982;76(6):830-2.

21 Soares RP, Cardoso TL, Barron T, Araã MS, Pimente PF, Turco SJ. Leishmania braziliensis: a novel mechanism in the lipophosphoglycan regulation during metacyclogenesis. Int J Parasitol. 2005 Mar;35(3):245-53. Doi:10.1016/j.ijpara.2004.12.008         [ Links ]

22 Soares RP, Macedo ME, Ropert C, Gontijo NF, Almeida IC, Gazzinelli RT. Leishmania chagasi: lipophosphoglycan characterization and binding to the midgut of the sand fly vector Lutzomyia longipalpis. Mol Biochem Parasitol. 2002 May;121(2):213-24.         [ Links ]

23 Souza AAA, Silveira FT, Silva FMM, Silva LA, Leão EF, Barata IR, et al. Flebotomíneos capturados e identificados no Campus II do Instituto Evandro Chagas - Ananindeua - Estado do Pará, Brasil. Rev Soc Bras Med Trop. 2009;42 Supl 1:441.

24 Tibayrenc M. The species concept in parasites and other pathogens: a pragmatic approach? Trends in Parasitol. 2006 Feb;22(2):66-70.Doi:10.1016/j.pt.2005.12.010         [ Links ]

 

 

Correspondência / Correspondence / Correspondencia:
Fernando Tobias Silveira
Instituto Evandro Chagas,
Seção de Parasitologia
Rodovia BR 316, km 07, s/n^o. Bairro: Levilândia
CEP: 67030-000
Ananindeua-Pará-Brasil
E-mail:fernandotobias@iec.pa.gov.br

Recebido em / Received / Recibido en: 21/1/2010
Aceito em / Accepted / Aceito en: 25/6/2010