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The genome of the heartworm, Dirofilaria immitis, reveals drug and vaccine targets.

ABSTRACT: The heartworm Dirofilaria immitis is an important parasite of dogs. Transmitted by mosquitoes in warmer climatic zones, it is spreading across southern Europe and the Americas at an alarming pace. There is no vaccine, and chemotherapy is prone to complications. To learn more about this parasite, we have sequenced the genomes of D. immitis and its endosymbiont Wolbachia. We predict 10,179 protein coding genes in the 84.2 Mb of the nuclear genome, and 823 genes in the 0.9-Mb Wolbachia genome. The D. immitis genome harbors neither DNA transposons nor active retrotransposons, and there is very little genetic variation between two sequenced isolates from Europe and the United States. The differential presence of anabolic pathways such as heme and nucleotide biosynthesis hints at the intricate metabolic interrelationship between the heartworm and Wolbachia. Comparing the proteome of D. immitis with other nematodes and with mammalian hosts, we identify families of potential drug targets, immune modulators, and vaccine candidates. This genome sequence will support the development of new tools against dirofilariasis and aid efforts to combat related human pathogens, the causative agents of lymphatic filariasis and river blindness.

SUBMITTER: Godel C

PROVIDER: S-EPMC3475251 | biostudies-literature | 2012 Nov

REPOSITORIES: biostudies-literature

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The genome of the heartworm, Dirofilaria immitis, reveals drug and vaccine targets.

Godel Christelle C Kumar Sujai S Koutsovoulos Georgios G Ludin Philipp P Nilsson Daniel D Comandatore Francesco F Wrobel Nicola N Thompson Marian M Schmid Christoph D CD Goto Susumu S Bringaud Frédéric F Wolstenholme Adrian A Bandi Claudio C Epe Christian C Kaminsky Ronald R Blaxter Mark M Mäser Pascal P

FASEB journal : official publication of the Federation of American Societies for Experimental Biology 20120813 11

The heartworm Dirofilaria immitis is an important parasite of dogs. Transmitted by mosquitoes in warmer climatic zones, it is spreading across southern Europe and the Americas at an alarming pace. There is no vaccine, and chemotherapy is prone to complications. To learn more about this parasite, we have sequenced the genomes of D. immitis and its endosymbiont Wolbachia. We predict 10,179 protein coding genes in the 84.2 Mb of the nuclear genome, and 823 genes in the 0.9-Mb Wolbachia genome. The ...[more]

PMID: 22889830

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Project description:BackgroundHeartworm (Dirofilaria immitis) in dogs is considered endemic in Australia, but the clinical heartworm disease caused by the heartworm is rare and prevalence is low. The mainstream prevention of the heartworm is based on macrocyclic lactone (ML) administration. The aim of this study was to confirm endemism of the heartworm under current Australian conditions using a cohort of recent microfilaria-positive dogs which were on variable heartworm prevention.MethodsA hotspot of canine heartworm antigen-positive and microfilaria-positive dogs has been detected recently in Queensland, Australia. Blood samples from 39 dogs from Queensland and two dogs from New South Wales were investigated for canine filarioids. Rapid antigen diagnostic tests capable of detection of D. immitis and real-time PCR for quantification and differentiation between D. immitis from Acanthocheilonema reconditum with quantification of microfilariae in canine blood samples, together with D. immitis specific real-time PCR assay, were applied to microfilaria-positive dogs. The P-glycoprotein genotype was determined to test whether Australian-sourced heartworm shared the same genetic markers as those suspected of ML-resistance in North America.ResultsOnly D. immitis was detected in the samples from Queensland and New South Wales, Australia. Using high resolution melt real-time PCR and D. immitis specific real-time PCR, the calculated microfilaria concentration ranged from 1 to 44,957 microfilariae/ml and from 7 to 60,526 microfilariae/ml, respectively. DNA sequencing of the PCR products confirmed D. immitis. Fifteen of the examined dogs were on putative, rigorous ML prevention. For the remaining dogs, compliance with heartworm prevention was unknown or reported as inconsistent. Wild-type genotype AA-GG of the P-glycoprotein locus of D. immitis sequence has been obtained for three blood samples. Due to the incomplete history, any suggestion of a loss of efficacy of MLs must be treated as 'remotely possible'. In the immediate future, records of preventative administration and annual antigen testing would be required to determine any problems with the efficacy of preventatives.ConclusionsThe prevalence of canine heartworm in Australia remains poorly understood. It is generally assumed to be low by veterinary practitioners. The localised increase in the study area confirms endemism of canine heartworm and a requirement for ongoing vigilance through annual heartworm testing to better understand the changing distribution of canine heartworm, client compliance, as well as to detect any change in ML-susceptibility.

Project description:BACKGROUND:For dogs and cats, chemoprophylaxis with macrocyclic lactone (ML) preventives for heartworm disease is widely used in the United States and other countries. Since 2005, cases of loss of efficacy (LOE) of heartworm preventives have been reported in the U.S. More recently, ML-resistant D. immitis isolates were confirmed. Previous work identified 42 genetic markers that could predict ML response in individual samples. For field surveillance, it would be more appropriate to work on microfilarial pools from individual dogs with a smaller subset of genetic markers. METHODS:MiSeq technology was used to identify allele frequencies with the 42 genetic markers previously reported. Microfilaria from ten well-characterized new isolates called ZoeKY, ZoeMI, ZoeGCFL, ZoeAL, ZoeMP3, ZoeMO, ZoeAMAL, ZoeLA, ZoeJYD-34, and Metairie were extracted from fresh blood from dogs. DNA were extracted and sequenced with MiSeq technology. Allele frequencies were calculated and compared with the previously reported susceptible, LOE, and resistant D. immitis populations. RESULTS:The allele frequencies identified in the current resistant and susceptible isolates were in accordance with the allele frequencies previously reported in related phenotypes. The ZoeMO population, a subset of the ZoeJYD-34 population, showed a genetic profile that was consistent with some reversion towards susceptibility compared with the parental ZoeJYD-34 population. The Random Forest algorithm was used to create a predictive model using different SNPs. The model with a combination of three SNPs (NODE_42411_RC, NODE_21554_RC, and NODE_45689) appears to be suitable for future monitoring. CONCLUSIONS:MiSeq technology provided a suitable methodology to work with the microfilarial samples. The list of SNPs that showed good predictability for ML resistance was narrowed. Additional phenotypically well characterized D. immitis isolates are required to finalize the best set of SNPs to be used for large scale ML resistance screening.

Project description:BACKGROUND:Canine heartworm disease, caused by Dirofilaria immitis, has global veterinary importance. In Australia, the prevalence of canine heartworm infection decreased markedly following the introduction of over-the-counter macrocyclic lactones. We aimed to estimate the prevalence of canine heartworm infection in at-risk populations of dogs in eastern Australia and analyse published prevalence data from Australia. METHODS:In total, 566 dogs from eastern Australia were tested for the presence of D. immitis antigen. Four cohorts were studied: pig-hunting dogs from Queensland (Cohort 1, n = 104), dogs from remote New South Wales (NSW) (Cohort 2, n = 332), urban pets from rural NSW (Cohort 3, n = 45) and ex-racing Greyhounds from Sydney, NSW (Cohort 4, n = 85). Serum samples were screened for D. immitis antigen using a reference laboratory microwell-based assay (DiroChek®) or a point-of-care immunochromatography test kit (Anigen Rapid®). Risk factors associated with the odds of D. immitis antigen seropositivity were identified using binary logistic regression models. Seropositive blood samples were tested for the presence and quantity of D. immitis DNA using a species specific real-time (q)PCR assay. A metanalysis of the Australian canine heartworm literature was conducted. RESULTS:The prevalence of dirofilariasis in pig-hunting dogs from Queensland (Cohort 1) was 12.5% (95% CI: 6.5-18.9%), with a subpopulation of dogs from Central Queensland having a prevalence of 21% (95% CI: 12.3-33.4%). Age was significantly associated with D. immitis antigen seropositivity (increased risk with increased age). The odds of being > 5 years versus ≤ 5 years was 3.7-times (95% CI: 1.1-12.5) greater in antigen positive versus antigen negative dogs. No D. immitis antigen positive dogs were detected in dogs from NSW (Cohorts 2-4). The Australian canine heartworm disease literature includes 98 peer-reviewed publications (1901-2019) with 30 studies reporting on D. immitis prevalence in dogs. Throughout the publication peak period (1980s), the primary antemortem diagnostic test was detection of microfilariae. CONCLUSIONS:Canine heartworm infection in dogs used for pig hunting is a previously unexplored topic in Australia. Pig-hunting dogs are infected with canine heartworm in Queensland, Australia, placing pet dogs and cats at increased risk of infection.

Project description:BACKGROUND:Macrocyclic lactone (ML) anthelmintics are used for chemoprophylaxis for heartworm infection in dogs and cats. Cases of dogs becoming infected with heartworms, despite apparent compliance to recommended chemoprophylaxis with approved preventives, has led to such cases being considered as suspected lack of efficacy (LOE). Recently, microfilariae collected from a small number of LOE isolates were used as a source of infection of new host dogs and confirmed to have reduced susceptibility to ML in controlled efficacy studies using L3 challenge in dogs. A specific Dirofilaria immitis laboratory isolate named JYD-34 has also been confirmed to have less than 100% susceptibility to ML-based preventives. For preventive claims against heartworm disease, evidence of 100% efficacy is required by FDA-CVM. It was therefore of interest to determine whether JYD-34 has a genetic profile similar to other documented LOE and confirmed reduced susceptibility isolates or has a genetic profile similar to known ML-susceptible isolates. METHODS:In this study, the 90Mbp whole genome of the JYD-34 strain was sequenced. This genome was compared using bioinformatics tools to pooled whole genomes of four well-characterized susceptible D. immitis populations, one susceptible Missouri laboratory isolate, as well as the pooled whole genomes of four LOE D. immitis populations. Fixation indexes (FST), which allow the genetic structure of each population (isolate) to be compared at the level of single nucleotide polymorphisms (SNP) across the genome, have been calculated. Forty-one previously reported SNP, that appeared to differentiate between susceptible and LOE and confirmed reduced susceptibility isolates, were also investigated in the JYD-34 isolate. RESULTS:The FST analysis, and the analysis of the 41 SNP that appeared to differentiate reduced susceptibility from fully susceptible isolates, confirmed that the JYD-34 isolate has a genome similar to previously investigated LOE isolates, and isolates confirmed to have reduced susceptibility, and to be dissimilar to the susceptible isolates. CONCLUSIONS:These results provide additional evidence for the link between genotype and the reduced susceptibility phenotype observed in such isolates as JYD-34. Further work on other isolates showing reduced susceptibility to ML is required to demonstrate the value of genetic analysis in predicting the response to ML chemoprophylaxis. The authors suggest that genetic analysis may be useful in helping to interpret the results of in vivo efficacy testing of ML heartworm preventives against D. immitis isolates.

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The genome of the heartworm, Dirofilaria immitis, reveals drug and vaccine targets.

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The genome of the heartworm, Dirofilaria immitis, reveals drug and vaccine targets.

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