Heartworm Preventive Resistance: Is it possible?
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Jeff&Vicki
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- Joined: Fri Mar 30, 2007 6:24 pm
- Location: SW Indiana
Heartworm Preventive Resistance: Is it possible?
They are running TV commercials about this in my area, so I started looking into it. There is a map on the home page that shows how many cases are reported across
the country. My area is a hot spot. Slide show map: http://www.heartwormsociety.org/veterin ... slide.html
Home page of American Heartworm Society: http://www.heartwormsociety.org/
Download the 2 page article here (excerpt below): http://www.heartwormsociety.org/AHS-Res ... icle-A.pdf
In certain areas of the United States, most notably the Mississippi Delta region, an inordinate number of dogs have become infected with heartworms while
reportedly taking preventive medication. Practitioners diagnosing these unexpected heartworm infections have begun to question the effectiveness of macrocyclic lactones.
Anecdotal evidence and preliminary scientific studies suggest that some populations of heartworms may behave differently when exposed to macrocyclic lactones.
In addition, a study presented at the 2010 Triennial Heartworm Symposium identified genetic variation in selected fragments of genes among different populations of
heartworm microfilariae. At this time it is not known what impact the presence of this genetic polymorphism has on heartworm resistance.
As a science-based organization, the American Heartworm Society acknowledges these findings as we consider all potential explanations regarding prevention failure.
Aggressive research efforts are being directed to study and potentially identify resistant strains of heartworms, but those studies may take several years to substantiate
a definitive conclusion. Meanwhile we must consider all options and evaluate all variables which might account for a lack of efficacy (LOE) in preventing heartworms and
devise options which can improve efficacy.
While considering the possibility of resistance, we must temper these early findings with the understanding that several other variables come into play.
Clearly, two common factors related to (LOE) cases are inconsistent administration of preventive medications and inappropriate testing intervals.
Imperfect testing can account for many assumed cases of LOE. Recent studies have also demonstrated that administration of macrocyclic lactones to pets with
prepatent infections will actually delay the development of heartworms.
Therefore, simply retesting pets 6 months after beginning a preventive regimen will miss infections that have delayed maturity.
For this reason, the American Heartworm Society recommends that three consecutive “negative” antigen tests 6 months apart must be obtained to potentially classify these
animals as heartworm disease “negative.”
It is also possible that as heartworm tests have become more sensitive (and therefore more accurate) veterinarians are able to identify infections not previously detectable by older generation tests.
In addition, increased exposure due to the presence of more mosquitoes OR more heavily infected mosquitoes may be involved.
the country. My area is a hot spot. Slide show map: http://www.heartwormsociety.org/veterin ... slide.html
Home page of American Heartworm Society: http://www.heartwormsociety.org/
Download the 2 page article here (excerpt below): http://www.heartwormsociety.org/AHS-Res ... icle-A.pdf
In certain areas of the United States, most notably the Mississippi Delta region, an inordinate number of dogs have become infected with heartworms while
reportedly taking preventive medication. Practitioners diagnosing these unexpected heartworm infections have begun to question the effectiveness of macrocyclic lactones.
Anecdotal evidence and preliminary scientific studies suggest that some populations of heartworms may behave differently when exposed to macrocyclic lactones.
In addition, a study presented at the 2010 Triennial Heartworm Symposium identified genetic variation in selected fragments of genes among different populations of
heartworm microfilariae. At this time it is not known what impact the presence of this genetic polymorphism has on heartworm resistance.
As a science-based organization, the American Heartworm Society acknowledges these findings as we consider all potential explanations regarding prevention failure.
Aggressive research efforts are being directed to study and potentially identify resistant strains of heartworms, but those studies may take several years to substantiate
a definitive conclusion. Meanwhile we must consider all options and evaluate all variables which might account for a lack of efficacy (LOE) in preventing heartworms and
devise options which can improve efficacy.
While considering the possibility of resistance, we must temper these early findings with the understanding that several other variables come into play.
Clearly, two common factors related to (LOE) cases are inconsistent administration of preventive medications and inappropriate testing intervals.
Imperfect testing can account for many assumed cases of LOE. Recent studies have also demonstrated that administration of macrocyclic lactones to pets with
prepatent infections will actually delay the development of heartworms.
Therefore, simply retesting pets 6 months after beginning a preventive regimen will miss infections that have delayed maturity.
For this reason, the American Heartworm Society recommends that three consecutive “negative” antigen tests 6 months apart must be obtained to potentially classify these
animals as heartworm disease “negative.”
It is also possible that as heartworm tests have become more sensitive (and therefore more accurate) veterinarians are able to identify infections not previously detectable by older generation tests.
In addition, increased exposure due to the presence of more mosquitoes OR more heavily infected mosquitoes may be involved.
"If there are no dogs in Heaven, then when I die I want to go where they went." .... Will Rogers