Thanks, and yes we did have them both on it. We took them both in for a regular check up, and having had gotten the pills online, the vet had us do another blood test for them. They were both positive, the vet explained that it could happen 2 ways, if we had missed doseage by 1 day or more, they were at risk, or simply because the mosquito's where we lived were and are still so bad that he is seeing record #'s of cases of heartworms this year. Dogs that he treats himself and supplies the heartworm preventative to them, are coming up positive. He is very upset by this. The mosquitos are terrible here, in South Texas, we lived in a bay city, with a river, and lots of storm drains where our house was. They are constantly spraying, we had to get vector control out to spray constantly for them. The fleas are just as bad, we didnt get a significant freeze this past winter, to kill the fleas and mosquitos, or standing water areas.
To explain the heartworm preventative technically, the pill kills the baby heartworms, so it isnt a prevatitive for them to not get the heartworm, the pill kills the babies so that they cannot mature into adult worms and invade the heart. So missing a dose by a day or so, can just hit the worm just right, and it could slip thru and mature, then once the worm is adult age, the heartworm pill will continue to kill the new babies, but has no effect on the adult worms. Which can inturn risk the animals life and organs, with the adult worm in there, fighting the medicine.
Heartworm resources, that i researched.
[url]http://www.petcaretips.net/heartworms_in_dogs.html[/url]
[url]http://www.vetinfo.com/doghw.html[/url]
[url]http://www.marvistavet.com/html/body_heartworm_prevention.html[/url]
[url]http://www.allpetsmacomb.com/parasites.html[/url]
and finally one that gave some conflicting advice
[url]http://www.danebytes.com/heartworm.htm[/url]