Genetic characterization of Hawaiian isolates of Plasmodium relictum reveals mixed-genotype infections.
BACKGROUND
The relatively recent introduction of a highly efficient mosquito vector and an avian pathogen (Plasmodium relictum) to an isolated island ecosystem with naïve, highly susceptible avian hosts provides a unique opportunity to investigate evolution of virulence in a natural system. Mixed infections can significantly contribute to the uncertainty in host-pathogen dynamics with direct impacts on virulence. Toward further understanding of how host-parasite and parasite-parasite relationships may impact virulence, this study characterizes within-host diversity of malaria parasite populations based on genetic analysis of the trap (thrombospondin-related anonymous protein) gene in isolates originating from Hawaii, Maui and Kauai Islands.


METHODS
A total of 397 clones were produced by nested PCR amplification and cloning of a 1664 bp fragment of the trap gene from two malarial isolates, K1 (Kauai) and KV115 (Hawaii) that have been used for experimental studies, and from additional isolates from wild birds on Kauai, Maui and Hawaii Islands. Diversity of clones was evaluated initially by RFLP-based screening, followed by complete sequencing of 33 selected clones.


RESULTS
RFLP analysis of trap revealed a minimum of 28 distinct RFLP haplotypes among the 397 clones from 18 birds. Multiple trap haplotypes were detected in every bird evaluated, with an average of 5.9 haplotypes per bird. Overall diversity did not differ between the experimental isolates, however, a greater number of unique haplotypes were detected in K1 than in KV115. We detected high levels of clonal diversity with clear delineation between isolates K1 and KV115 in a haplotype network. The patterns of within-host haplotype clustering are consistent with the possibility of a clonal genetic structure and rapid within-host mutation after infection.


CONCLUSIONS
Avian malaria (P. relictum) and Avipoxvirus are the significant infectious diseases currently affecting the native Hawaiian avifauna. This study shows that clonal diversity of Hawaiian isolates of P. relictum is much higher than previously recognized. Mixed infections can significantly contribute to the uncertainty in host-pathogen dynamics with direct implications for host demographics, disease management strategies, and evolution of virulence. The results of this study indicate a widespread presence of multiple-genotype malaria infections with high clonal diversity in native birds of Hawaii, which when coupled with concurrent infection with Avipoxvirus, may significantly influence evolution of virulence.
Jarvi
Susan I
SI
Department of Biology, College of Arts & Sciences, College of Pharmacy, University of Hawaii at Hilo, 200 West Kawili Street, Hilo HI 96720, USA. jarvi@hawaii.edu
Farias
Margaret E M
ME
Atkinson
Carter T
CT
D000818:Animals; D000835:Animals, Wild; D018150:Avipoxvirus / Q000235:genetics / Q000472:pathogenicity; D001717:Birds / Q000235:genetics / Q000469:parasitology*; D020022:Genetic Predisposition to Disease; D005838:Genotype; D006239:Haplotypes; D006254:Hawaii; D008289:Malaria, Avian / Q000235:genetics / Q000469:parasitology*; D010961:Plasmodium / Q000235:genetics* / Q000254:growth & development / Q000302:isolation & purification* / Q000472:pathogenicity; D016133:Polymerase Chain Reaction; D012150:Polymorphism, Restriction Fragment Length; D011213:Poxviridae Infections / Q000235:genetics / Q000821:virology; D015800:Protozoan Proteins / Q000096:biosynthesis / Q000235:genetics / Q000502:physiology
D015800:Protozoan Proteins; C069428:thrombospondin-related adhesive protein, protozoan