top of page
  • Writer's pictureDr. P

Aussies, Mosquitos and Heartworm, oh my!

Updated: Mar 27, 2019

For 35 years, I have told my clients in Southern California that we live in the magic Orange County bubble and that we don't have to worry about mosquitos and heartworm, with the caveat that, someday we may be at risk, as we do have the mosquito vector in Southern California. While our statistics are low , I have treated my first cases of discovered heartworm in native California dogs. It was a 6 month treatment, not inexpensive, the injections were expensive and painful, and the other meds had numerous side effects.

In a recent Conti Symposium at UC Irvine, the Infectious Disease Specialist speakers ( if you want a definition of brilliant, sit in a series of lectures by world renowned CDC researchers and infectious disease specialists!) outlined the significant uptick in mosquito vector diseases in the southland...Heartworm, West Nile Virus, and more recently, there is a concern for Zika virus. Interestingly, an increase in West Nile cases occurred during drought seasons, and they had suspected that the heavy rains washed clean the drain basins, while the dryer seasons allowed small puddles in our drain systems to propagate mosquitos ( just an interesting sidenote! ) They even found mosquito larvae in a wet, crumpled Frito's bag...

So what to do , what to do.....

Mosquitos love standing water, but I have even found larvae in one of my fountains. I now add chlorine bleach to my fountains at home. Search your yard for standing water. Flower pot basins, kids plastic pools.. Vector control is available to help you assess your property and is sending staff door to door in high risk areas. Use mosquito repellent in the evening, and if a high risk area, during the day if outside. The Aedes mosquito (Zika vector) feeds a couple hours after sunrise and a couple hours before sunset, so they essentially are "daytime" feeders.

For your 4 leggers...

There are great products available that provide protection from Heartworm, Ticks and Fleas. The options are drip on products, oral medications and collars. Some of these products do contain an ivermectin or milbemycin. The Aussie breeds, Collies and Shelties and some other breeds as well, have a high incidence of MDR1 affected or MDR1 carrier status. (Some researches suspect as high as 75% in the Collie breed.) These affected or carrier dogs have a mutation of the ABCB1 gene that decreases or prohibits the P-glycoprotein pump's ability to limit absorption, distribution and excretion of certain drugs. These dogs can experience life threatening neurologic problems, seizures, blindness or death.

These drugs include:

Acepromazine (tranqulizers)

Butorphanol (pain drug)

Ivermectin, Moxidectin, Milbemycin, Selamectin

Loperamide ( anti-diarrheal medication)

Some of my Aussie loving friends are very frightened at the thought of using ivermectin related products on their dogs.

According to the research at Washington State University, the dosage of ivermectin as well as selamectin, milbemycin and moxidectin in heartworm preventative is SAFE in dogs even with the mutation or carrier status of MDR1. These dosings are in MICROGRAMS and can safely prevent and control heartworm. However, WSU recommends NOT using combination drugs for heartworm.


HIGHER DOSES that are used to treat mange mites WILL CAUSE neurotoxicity in dogs that are homozygous for MDR1 (mutant /mutant) and CAN cause toxicity in dogs that are heterozygous for MDR1 (Mutant/normal). IF THE DOG IS NOT TESTED, DO NOT USE THESE HIGHER DOSES.

RANCH DOGS... horses and cattle are dewormed with pastes that contain ivermectin. This is a high risk of exposure as the dogs can (and will) find the paste tubes and chew or eat them, and seizure and die.


A simple cheek swab can test your dog! See Washington State University Website at: for more information......

and careful out there!!!!

337 views0 comments

Recent Posts

See All


bottom of page