Fleas and Ticks | Newsletters

Imminent Threat

The most common parasites we encounter on our dogs and cats are fleas (Ctenocephalides felis – the common cat flea) and ticks (of which we have at least 12 different species to worry about in South Africa). Ticks and fleas present on an animal’s coat will cause irritation to the host on their own, but they also have the ability to transmit diseases to the animals they infest as well as pet owners. First we will discuss fleas and then move onto ticks and the challenges they pose.

Fleas seen on an animal today were laid as eggs 3-8 weeks ago, which means that we have already missed out on 2-3 generations of fleas due to their short life cycle (14-42 days, depending on the prevailing environmental conditions). In order for the life cycle of the flea to continue, the enviromental temperature must be > 10o C and the relative humidity should be greater than 50%. In South Africa, the latter conditions are present in most places throughout the year, especially once the sun comes up in the morning. The implication of the latter is that fleas remain a problem throughout the year in South Africa because our winters are not severe enough to stop the life cycle, which allows the environmental load of fleas to increase when we are not treating our pets. Most of the developing fleas will remain protected inside a cocoon (this stage is called the pupa stage, which is essentially a sub-adult flea inside a protective shell which also serves to nourish the developing flea for up to a year sometimes) in the environment and wait for the environmental conditions to improve or for a host to be present before they hatch. Essentially, the flea life cycle slows down in winter but it never stops. Once spring and summer arrives, a large number of “new” fleas emerge from pupae in the environment which resembles a seasonal pattern.

Having discussed environmental load, it is absolutely crucial that we understand what we are dealing with. When looks at the various stages of the flea life cycle, we see that 95-99% of the flea population is found in the surrounding environment, while the remaining 1- 5% is on the actual animal hosts. The importance of this fact is that every pet owner that is attempting to eradicate a flea infestation needs to understand that when they are treating their infested pet, they are only treating 1-5% of the problem. The implication of the latter is two-fold: (a) products that kill the environmental stages of fleas are also required before we gain control of the infestation, and (b) because we are treating such a small percentage of the population, eradication of the infestation is a slow process that usually takes a minimum of 2 months to achieve. The golden rule is that we need a product that kills adult fleas on the animal infested, as well as a product that kills the environmental stages of the flea as well (at least the eggs; these products are referred to as insect growth regulators and they prevent eggs from hatching thereby reducing environmental infestation). The latter is non-negotiable and these products are readily available through a variety of sources (veterinary practices, vet shops, etc.)

We need to gain an understanding of the biologic and epidemiologic factors responsible for persistent flea infestations:

• For a pet to have “Fleas” there must be eggs, larvae, pupae and emerging fleas somewhere in the property. That means we need to go back in time, at least 2 months when the 1st generation of fleas began to breed and multiply.
• Pets do not acquire fleas directly from another flea infested dog/cat. Since the adult cat flea is a permanent external parasite, metabolically dependent upon a constant host relationship, direct flea transfer between pets is a rare occurrence. Fleas we see on our pets and in our homes came from flea eggs laid 3-8 weeks previously. Those initial few fleas came from flea eggs deposited by neighbor’s pets, feral dogs & cats or possibly flea infested wild mammals. Those eggs deposited in the outdoor premises developed to the adult stage and jumped on their dog/cat or even occasionally the pet owner/humans on the same premises.
• Most of us never see the first 2 - 3 fleas our pets acquire. What we actually react to is often the 2nd or 3rd generation. Those initial few fleas (trickle infestation), mate within a few hours and females start laying eggs within 24 hours and in a few days are producing up to 40 – 50 eggs/day/flea.
• Fleas deposit their eggs into the coat of the pet with the eggs then falling out of the coat into the premises where they ultimately develop in a few weeks to the adult flea. By the time we as pet owners react and take our pet(s) to the veterinarian there are already flea eggs, larvae, pupae and emerging fleas in the home and protected outdoor source points (”environmental hotspots”), which is why it may take several weeks to get adequate flea control and rarely complete elimination.
• Products do not kill fleas instantaneously and while products may have a rapid neurotoxic effect that may be perceived as “clinical repellency”, the repellent and antifeeding effect against fleas may be poor and may even be non-existent. While a few fleas may die within minutes, most will actually feed prior to dieing often many hours later. Therefore when we see a few fleas on our pets 1 - 3 weeks after treatment we should not incorrectly assume that the product is failing. Due to the contact neurotoxic action of these compounds newly acquired fleas often are only killed after 18 – 48 hours, depending on the product being used.
• Close scrutiny of treated pets in an infested environment will almost always result in fleas being observed for up to 8 weeks and occasionally longer.
• Products kill most newly acquired fleas before egg production is initiated (24 hours), however, some level of flea survival and reproduction does occur prior to next application. This occurs 1) because the speed of flea kill slows during 3rd and 4th week after application due to decreased insecticide levels (with all modern insecticide products),
  2) incorrect application of the product results in under-dosing - a very common example is the products packed in plastic ampoules, requiring that one squeezes the contents out, however, once the pressure is released it creates a suction force and some of the liquid is sucked back into the ampoule; a survey conducted in recent years in Australia and USA found that 40% of ampoule users were under-dosing in this way 3) Frequent bathing/swimming can reduce insecticide levels and 4) Genetic variability of flea isolates resulting in differences in insecticide susceptibility (this refers to the classic “bell-curve” of population dynamics).
• The factors that result in <100% residual flea kill and allow for limited egg production from surviving fleas have been recognized for almost a decade. Therefore the use of Integrated Flea Control (IFC) utilizing Insect Growth Regulators (IGRs) that render flea eggs nonviable is absolutely essential.

When a flea infested pet is identified, there are 3 goals that must be achieved:

(a) Relieving pet of its current discomfort - kill fleas A.S.A.P. on the pet(s); I personally find that using a topical spray formulation immediately is most effective; use the spray as directed and use latex gloves to part the hair so that the active ingredients can reach the skin. Then follow-up on that treatment with a registered spot-on in 3 days time, and maintain treatments at least every 4 weeks. Remember that some of these products are safe enough to use every 2 weeks if required initially, to allow us to gain control of a flea burden faster – check with the manufacturer if the product you wish to use can be applied more often than 4 weeks initially. Dips and insecticidal shampoos may also be used but they do not last as long as the spot-ons, and they are much more labour-intensive because the dogs need to be restrained during the process.

(b) Eliminate the premise infestation - eliminate immature life stages and emerging fleas,
The crashing flea population will control itself no matter what product you use, and you will see results within 1-7 days. Biologically speaking, no product can ever do that even if it was to be used under the ideal conditions of a laboratory. That means that the only explanation why such a thing would happen, is that the population was in the process of dying out naturally anyway.

Waining and static flea populations take substantially longer to control and you will still see fleas on your pets but at the expected amounts of 1-3 fleas at any given time. If the 1-3 fleas are sometimes and sometimes not, then we are dealing with a waining flea population. Treating your pets when experiencing the effects of a waining flea population, results will be seen within 1-5 weeks.

If the pets always have 1-3 fleas visible on their coat at any given time, then we are dealing with a static flea population. Treating pets in this scenario may take up to 8 weeks to achieve low levels of infestations that are either not easily visible nor irritant to the coat of the animals (no scratching is seen).

The hardest flea infestations to control will be when we have a surging flea population and the number of fleas hatching in the environment and subsequently jumping onto our pets is far greater than what we can kill with our spot-on and spray products. These infestations can sometimes require continuous, diligent and timeous treatments for the next 4-6 months and often require the change of season to assist in slowing down the reproduction of the fleas in the environment. Although the reproduction of the fleas in the environment will slow down it will rarely stop in South Africa (except in isolated areas of the country where climatic conditions may force relative humidity to drop below 50% and temperatures below 10 degrees Celcius). The rest of South Africa will still experience mild to moderate flea infestations througout the year, especially in areas along the coast where the humidity is higher than 50% throughout the course of the year.

Control of premise life stages can be achieved without direct treatment of the premises (in most cases; rarely direct treatment of premises is indicated) through a combination of residual adulticidal activity (killing newly acquired fleas) and ovicidal activity (rendering eggs of surviving fleas nonviable). The latter will only occur if the product chosen contains an adulticidal compound (fipronil, imidacloprid, selamectin, and pyrethroids) as well as an Insect Growth Regulator compound (methoprene, pyriproxifen and fenoxycarb). If not, then direct treatment of the environment is absolutely essential. This well established concept of Integrated Flea Control (IFC) is also termed “Breaking the life cycle at the host level”. This approach essentially turns the treated dog or cat into a “living flea vacuum”. Over the next 3 - 8 weeks (occasionally longer) the flea eggs already in the premise develop into larvae, then into pupae and finally into adult fleas. As fleas emerge and jump on treated pets most are killed by the residual adulticide and if a few survive and lay eggs, those eggs are killed by the ovicidal activity. The population is driven to “extinction” through elimination of reproduction. This time period from treatment until control is achieved (elimination of all premises life stages) is called the “Development Window”.

In addition destroy refuge areas for fleas - they like shaded/covered and sanded areas (exposed soil). Remove or burn tall grass, brush piles, and weeds between runs and fences and along buildings; the latter allows for sunlight penetration to cause desiccation or remaining immature flea life stages - larvae and nymphs especially. Pupae remain resistant and will probably only be destroyed by fire.

I would personally avoid fumigation and pesticide services as toxic compounds inevitably land up on plates and bowls of pets which subsequently contributes to acute poisonings and gastrointestinal disease.

(c) Prevention - provide for long term flea control preventing recurrence of an infestation simply by following the manufacturer’s recommendations on IFC. The latter usually means monthly treatment all year round!

Fleas infestations can lead to flea allergy dermatitis in dogs and cats, transmit tapeworm, as well as a number of diseases that can affect human beings as well (cat scratch disease, Haemoplasmosis, Rickettsia felis, etc.)

Tick control

It is crucially important to understand that there are a very large number of tick species (at least 12 species) that attack our beloved pets and all products have been tested only against a small number of those tick species – usually the tick species that are deemed most important for transmitting diseases such as biliary and Ehrlichiosis. When we find ticks on our dogs and cats we should identify them and check whether our choice of spot-on will offer us protection (Ask the manufacturers). If the product has never been tested against the species of tick in question, we cannot expect any great results. If it so happens that the product is effective against that species, we can consider that as a bonus.

What constitutes a “repellent” is not always clear – technically, there is no such thing currently on the market, as all available insecticides are contact-insecticides! That means that the parasite must come in contact with the parasiticide in order to be killed.

Since tick products do not kill or repel all ticks instantly (can take up to 48 hours for a tick to die after coming into contact with an insecticidal product), so we shouldn't get the impression that the products are not performing as well as expected. In these situations, consider additional tick-control measures. Destroy refuge areas for ticks and tick wildlife hosts. Removing or burning tall grass, brush piles, and weeds between runs and fences and along buildings can kill some ticks outright, allows for sunlight penetration to cause desiccation or remaining ticks and can reduce harborage for wildlife tick hosts.

We have absolutely minimal control over tick populations in the environment. The majority of ticks (99, 99%) are on alternative hosts and in the environment, and not on pets. This is due in large part to the multitude of wildlife hosts and immature ticks in the environment.