Guide to Preventing Parasites.pdf - Royal Canin Canada

- In animals that are unprotected during the transmission season and that might be
harbouring parasites aged 10 weeks or older, monthly treatment for an entire year should
be initiated immediately.
- A lack of efficacy has been reported for all the macrocyclic lactones used in canine
heartworm disease prophylaxis. An annual screening test is therefore strongly
recommended.
- For adulticide treatment, it is strongly advisable to administer a first dose of
melarsomine, followed four to six weeks later by two doses separated by a 24-hour
interval. This protocol lowers the risks inherent in the treatment.
- Microfilaricide treatment is initiated as soon as a diagnosis is made. Milbemycin seems
to be the drug with the greatest microfilaricidal effect. After the fist dose is administered,
the dog should be monitored because of the risk associated with the death of a large
number of microfilariae. Major reactions were observed in dogs whose microfilaria count
had been estimated to be as low as 5,000 per millilitre of blood (30 to 40 microfilariae per
microscope field at x10 magnification in the filtration test). The reasons for initiating this
treatment before administering an adulticide are to reduce the number or circulating
microfilariae, to eliminate the migrating third- and fourth-stage larvae, and to reduce the
adult worm mass by inhibiting the female’s reproductive system. In addition, it is not
known how effective melarsomine is against larvae aged 4 months or less. The risk of
thromboembolism during subsequent adulticide treatments will be reduced accordingly. It
is advisable to delay adulticide treatment for six months.
- The long-term use (12 months) of a macrocyclic lactone is beneficial in animals that are
infected but that display no clinical signs and have very few or no radiologically
documented pulmonary lesions and few or no microfilariae. Ivermectin seems to give the
best results in such cases, mainly because if its long-term lethal effect on young adult
worms. However, this approach does not seem to bring about improvement in chronically
infected animals with major clinical signs. If this type of treatment is administered to
such an animal, it is important to do a follow-up two or three times a year.
- Certain macrocyclic lactones now have a residual effect that makes them more
effective, but for now, it is not advisable to lengthen the interval between treatments.
Additional comments
Annual screening test for all dogs: It has been shown that drugs cannot provide 100%
protection against heartworms. This is probably the only reason why the AHS has called
for a shorter interval between screening tests. Before applying this measure to all dogs,
one should take the following points into consideration. Even a low parasite load can lead
to the appearance of microfilariae in the blood and permit transmission of the infection,
which goes against the main objective of our intervention. If infection occurs, it will, in
all probability, be by a small number of worms, which do not constitute a threat to the
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