Analysis of the trap gene provides evidence for the role of elevation and vector abundance in the genetic diversity of Plasmodium relictum in Hawaii.

BACKGROUND: The avian disease system in Hawaii offers an ideal opportunity to investigate host-pathogen interactions in a natural setting. Previous studies have recognized only a single mitochondrial lineage of avian malaria (Plasmodium relictum) in the Hawaiian Islands, but cloning and sequencing of nuclear genes suggest a higher degree of genetic diversity. METHODS: In order to evaluate genetic diversity of P. relictum at the population level and further understand host-parasite interactions, a modified single-base extension (SBE) method was used to explore spatial and temporal distribution patterns of single nucleotide polymorphisms (SNPs) in the thrombospondin-related anonymous protein (trap) gene of P. relictum infections from 121 hatch-year amakihi (Hemignathus virens) on the east side of Hawaii Island. RESULTS: Rare alleles and mixed infections were documented at three of eight SNP loci; this is the first documentation of genetically diverse infections of P. relictum at the population level in Hawaii. Logistic regression revealed that the likelihood of infection with a rare allele increased at low-elevation, but decreased as mosquito capture rates increased. The inverse relationship between vector capture rates and probability of infection with a rare allele is unexpected given current theories of epidemiology developed in human malarias. CONCLUSIONS: The results of this study suggest that pathogen diversity in Hawaii may be driven by a complex interaction of factors including transmission rates, host immune pressures, and parasite-parasite competition.

Quantitative PCR estimates Angiostrongylus cantonensis (rat lungworm) infection levels in semi-slugs (Parmarion martensi).

The life cycle of the nematode Angiostrongylus cantonensis involves rats as the definitive host and slugs and snails as intermediate hosts. Humans can become infected upon ingestion of intermediate or paratenic (passive carrier) hosts containing stage L3 A. cantonensis larvae. Here, we report a quantitative PCR (qPCR) assay that provides a reliable, relative measure of parasite load in intermediate hosts. Quantification of the levels of infection of intermediate hosts is critical for determining A. cantonensis intensity on the Island of Hawaii. The identification of high intensity infection 'hotspots' will allow for more effective targeted rat and slug control measures. qPCR appears more efficient and sensitive than microscopy and provides a new tool for quantification of larvae from intermediate hosts, and potentially from other sources as well.

Taqman real-time PCR detects Avipoxvirus DNA in blood of Hawai'i 'amakihi (Hemignathus virens).

BACKGROUND: Avipoxvirus sp. is a significant threat to endemic bird populations on several groups of islands worldwide, including Hawai'i, the Galapagos Islands, and the Canary Islands. Accurate identification and genotyping of Avipoxvirus is critical to the study of this disease and how it interacts with other pathogens, but currently available methods rely on invasive sampling of pox-like lesions and may be especially harmful in smaller birds. METHODOLOGY/PRINCIPAL FINDINGS: Here, we present a nested TaqMan Real-Time PCR for the detection of the Avipoxvirus 4b core protein gene in archived blood samples from Hawaiian birds. The method was successful in amplifying Avipoxvirus DNA from packed blood cells of one of seven Hawaiian honeycreepers with confirmed Avipoxvirus infections and 13 of 28 Hawai'i 'amakihi (Hemignathus virens) with suspected Avipoxvirus infections based on the presence of pox-like lesions. Mixed genotype infections have not previously been documented in Hawai'i but were observed in two individuals in this study. CONCLUSIONS/SIGNIFICANCE: We anticipate that this method will be applicable to other closely related strains of Avipoxvirus and will become an important and useful tool in global studies of the epidemiology of Avipoxvirus.

A nucleotide-constrained single base extension method for improved detection of minority alleles in Plasmodium.

In genetically mixed Plasmodium infections, minority alleles may have a significant role in drug resistance and other responses to selective pressures. Many available methods to detect single nucleotide polymorphisms representing minority alleles either are not sensitive enough to detect these rare alleles or are limited in the number of loci to be screened in a single reaction. In order to achieve highly sensitive, multiplex SNP genotyping, we have developed a nucleotide-constrained method based on the traditional single base extension approach. Here, we report results when using standard and nucleotide-constrained reactions to determine alleles at nine SNP loci in the trap gene of Plasmodium relictum. This innovative method offers great improvements in detection limits while maintaining the accuracy and multiplex capabilities of single base extension SNP genotyping.

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. CONCLUSION: 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.