Control of fleas and flea-induced diseases requires a considerable effort by both pet owners and veterinarians. Although convenient
and effective flea control products are available, successful flea management remains a challenge for many pet owners. The
reasons we still experience flea problems can usually be explained by a lack of understanding of the flea life cycle or a
lack of owner compliance.
Flea life cycle
First, let's look at aspects of the flea life cycle that are important in flea development and survival. Female fleas begin
egg production within 24 to 36 hours of taking their first blood meal. Females reach peak egg production at 40 to 50 eggs
per day — that's about 1,300 eggs during their first 50 days on a host. They continue to produce eggs at a gradually declining
rate for more than 100 days. The entire life cycle can be completed in as little as 12 to 14 days, or it can be prolonged
up to 174 days, depending on temperature and humidity.
It's easy to see that if flea infestations are left uncontrolled for just a brief period, flea populations (first in the environment,
then on the pet) can increase at astonishingly rapid rates. That said, in many regions of the country — and indoors in all
regions — flea development usually slows during the cooler temperatures of late fall, winter and spring months. But even during
these times, development does not cease entirely.
Flea control compliance
The second major reason for failure to control fleas is the presumption that since fleas are not visible, prevention can be
discontinued. However, the number of fleas visible on a pet represents only 5 percent of the total number of fleas on the
pet and in the environment. The fleas are there, even if you are not seeing them.
Recent research insights
Now for a more convincing argument for year-round control: Colleagues and I have been conducting research for several years
on the susceptibility of fleas from around the world to modern flea control products — specifically imidacloprid, a topical
flea adulticide. The purpose of this research is to monitor the susceptibility of national and regional isolates of fleas
to this commonly used flea control product. Our intention is to detect if and when resistance develops to imidacloprid and
to develop countermeasures should we document resistant fleas. Fortunately, we have yet to identify flea isolates anywhere
in the world that are resistant to imidacloprid. That is good news. However, some unexpected additional information emerged
from our examination of more than 1,300 flea isolates.
We noticed that the greatest numbers of fleas were sent to us during the months of August, September and October (Figure 1).
Since our submitted samples are most numerous during those three months, we can presume that that is an indication of the
magnitude of the flea populations on pets during those times. The abiotic factors (temperature, humidity, soil type) that
drive the flea life cycle are the reasons that as we move from spring to summer to early fall, the numbers of submitted samples
increases. As temperatures and relative humidity increase, the fleas on dogs or cats are better able to reproduce. Therefore,
even a small (often unnoticed) population can become an overwhelming problem in a short period.
Figure 1: Flea isolates collected by month (2001-2008)
The numbers of submitted samples (Figure 1), which are a reflection of the total number of fleas on pets, were least in December,
January, February, March and April. Lower temperature and humidity results in decreased reproductive rates of fleas at these
times. This does not imply that fleas have disappeared. It simply means that rates of reproduction have declined and that
many fleas lie waiting in the environment for better conditions in which to reproduce. These findings suggest that veterinarians
need to be more adamant about year-round use of products, and clients need to be more compliant in using flea products year-round
to prevent the surge in populations evident in August, September and October.