Mosquito-borne heartworm Dirofilaria immitis in dogs from Australia

Abstract

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.Electronic supplementary materialThe online version of this article (doi:10.1186/s13071-016-1821-x) contains supplementary material, which is available to authorized users.

Rhipicephalus sanguineus sensu lato from dogs and dromedary camels in Riyadh, Saudi Arabia: low prevalence of vector-borne pathogens in dogs detected using multiplexed tandem PCR panel

“…The multiplexed assay (MT-PCR) outcome was verified using pathogen-specific assays that detect and identify the target vector-borne pathogens (Harrus et al 2011, Otranto et al 2011, Barker et al 2012, Nguyen et al 2016. The implementation of internal controls in the MT-PCR assay enables direct confirmation of adequacy and inhibition.…”

Pig-hunting dogs are an at-risk population for canine heartworm (Dirofilaria immitis) infection in eastern Australia

“…These preventatives did not require a prescription and could be purchased across the counter from veterinary clinics, pet stores and (later) from online retail outlets and supermarkets [11,12]. In 2016, despite these measures, an apparent re-emergence of D. immitis infection and canine heartworm disease was documented in pet dogs in Central Queensland [13]. Apart from the impact of prophylactic therapy, factors affecting the prevalence of canine heartworm disease in Australia are incompletely understood.…”

Is canine heartworm (Dirofilaria immitis) endemic to South Australia?

“…D irofilaria immitis is a blood‐borne nematode that causes cardiopulmonary dirofilariasis, commonly called heartworm disease, a potentially lethal infection disturbing the cardiorespiratory system . The primary host of D. immitis is the domestic dog.…”

“…Canine heartworm is a vector‐borne disease with nematode larvae transmitted between definitive hosts by mosquitoes ( Culicidae spp.) . The lifecycle of D. immitis is approximately 7–9 months, with larval stages L1–L3 occurring in mosquito vectors.…”

“…In Australia, few studies have been conducted on the current prevalence and incidence of D. immitis infection. Recent reports have focussed on the prevalence of circulating microfilaria in historically endemic areas, such as Queensland and New South Wales . However, there is no evidence available regarding current prevalence of canine heartworm in South Australia (SA), with the most recent study published in 1992 which reported low level heartworm incidence of 1% .…”