Jump to content
BC Boards
Sign in to follow this  
Mark Billadeau

New literature on heartworm preventative resistance

Recommended Posts

Macrocyclic lactone resistance in Dirofilaria immitis: Failure of heartworm preventives and investigation of genetic markers for resistance

Veterinary Parasitology
15 June 2015, Vol.210(3):167178, doi:10.1016/j.vetpar.2015.04.002

Abstract
Macrocyclic lactone (ML) endectocides are used as chemoprophylaxis for heartworm infection (Dirofilaria immitis) in dogs and cats. Claims of loss of efficacy (LOE) of ML heartworm preventives have become common in some locations in the USA. We directly tested whether resistance to MLs exists in LOE isolates of D. immitis and identified genetic markers that are correlated with, and therefore can predict ML resistance. ML controlled studies showed that LOE strains of D. immitis established infections in dogs despite chemoprophylaxis with oral ivermectin or injectable moxidectin. A whole genome approach was used to search for loci associated with the resistance phenotype. Many loci showed highly significant differences between pools of susceptible and LOE D. immitis. Based on 186 potential marker loci, Sequenom® SNP frequency analyses were conducted on 663 individual parasites (adult worms and microfilariae) which were phenotypically characterized as susceptible (SUS), confirmed ML treatment survivors/resistant (RES), or suspected resistant/loss of efficacy (LOE) parasites. There was a subset of SNP loci which appears to be promising markers for predicting ML resistance, including SNPs in some genes that have been associated with ML resistance in other parasites. These data provide unequivocal proof of ML resistance in D. immitis and identify genetic markers that could be used to monitor for ML resistance in heartworms.

Abbreviations
ML, macrocyclic lactones

LOE, loss of efficacy

SUS, susceptible

RES, survivor/resistant

mf, microfilariaI

VM, ivermectin

MO, milbemycin oxime

MOX, moxidectin

Share this post


Link to post
Share on other sites

Mark,

 

So what should we do to make sure our dogs don't get hearworms ? At the present time I am using Ivermectin. Is it a just wait and see kind of thing ?

 

 

 

thanks

Share this post


Link to post
Share on other sites

We should keep doing what we've been doing. Be sure to not miss a dose and if you are using a livestock wormer for your dogs make sure you are giving at least the minimum effective dose every time; do not under dose.

Share this post


Link to post
Share on other sites

While resistance has been confirmed in heartworms the spread of the alleles that confer resistance is expected to be slow and the drugs used to treat heartworm infections are sill effective. (see attached review).

Additionally, there are ongoing studies to determine the mode of resistance which will allow for developing new preventatives which work around this mode of resistance.
ABC-B transporter genes in Dirofilaria immitis

The emergence of macrocyclic lactone resistance in the.pdf

Share this post


Link to post
Share on other sites

Join the conversation

You can post now and register later. If you have an account, sign in now to post with your account.

Guest
Reply to this topic...

×   Pasted as rich text.   Paste as plain text instead

  Only 75 emoji are allowed.

×   Your link has been automatically embedded.   Display as a link instead

×   Your previous content has been restored.   Clear editor

×   You cannot paste images directly. Upload or insert images from URL.

Sign in to follow this  

×
×
  • Create New...