Heartworms developing resistance to monthly preventatives
After hurricane Katrina there have been increasing reports of loss of effectiveness (LOE) for heartworm preventatives in the Gulf coast area. There have been many hypothesis for this increasing LOE.
Lack of consistent dosing with the monthly preventative has been a major contributor to the increasing reports of LOE.
Heartworm ‘lack of effectiveness’ claims in the Mississippi delta: Computerized analysis of owner compliance – 2004–2011
I have wondered if the number of microfilariae (immature worms) being injected into dogs each month has increased above the number that was used to establish the minimum effective dose decades ago (100 microfilariae). In other words more immature worms are injected into the dog between each month treatment could require more drug each month to kill them all. I have seen some literature which supports the increase load in mosquitos and/or the increase in infected mosquitos.
The development of resistance to macrocyclic lactones (class of drugs of monthly preventatives) by the heartworms.
Establishment of macrocyclic lactone resistant Dirofilaria immitis isolates in experimentally infected laboratory dogs
A very recently published study has located in the heartworms from two dogs infected with suspected resistant worms, genetic mutations that are associated with drug resistance in other parasites.
Macrocyclic lactone resistance in Dirofilaria immitis: Failure of heartworm preventives and investigation of genetic markers for resistance
These data indicate there is a subpopulation of Dirofilaria immitis (heartworms) that likely have genetic mutations providing resistance to all monthly heartworm preventatives. This needs to be confirmed and then a survey of infected mosquitos needs to be performed to determine the prevalence of this resistant subpopulation.
Lack of consistent dosing with the monthly preventative has been a major contributor to the increasing reports of LOE.
Heartworm ‘lack of effectiveness’ claims in the Mississippi delta: Computerized analysis of owner compliance – 2004–2011
I have wondered if the number of microfilariae (immature worms) being injected into dogs each month has increased above the number that was used to establish the minimum effective dose decades ago (100 microfilariae). In other words more immature worms are injected into the dog between each month treatment could require more drug each month to kill them all. I have seen some literature which supports the increase load in mosquitos and/or the increase in infected mosquitos.
The development of resistance to macrocyclic lactones (class of drugs of monthly preventatives) by the heartworms.
Establishment of macrocyclic lactone resistant Dirofilaria immitis isolates in experimentally infected laboratory dogs
A very recently published study has located in the heartworms from two dogs infected with suspected resistant worms, genetic mutations that are associated with drug resistance in other parasites.
Macrocyclic lactone resistance in Dirofilaria immitis: Failure of heartworm preventives and investigation of genetic markers for resistance
These data indicate there is a subpopulation of Dirofilaria immitis (heartworms) that likely have genetic mutations providing resistance to all monthly heartworm preventatives. This needs to be confirmed and then a survey of infected mosquitos needs to be performed to determine the prevalence of this resistant subpopulation.
