To My Quyen,
Nguyen Khanh Thuan, Nguyen Phuc Khanh, Nguyen Thanh Lam*
1. Introduction
Fleas are small wingless insects that feed on animal blood. In addition to being a nuisance, they can also transmit diseases and cause allergies or anemia. There are more than 2,200 species of fleas recognized worldwide. In North America, only a few species commonly infest house pets. Two common species of flea are the cat flea (Ctenocephalides felis) and the dog flea (Ctenocephalides canis). However, most of the fleas found on both dogs and cats are cat fleas. Fleas cause severe irritation in other animals and humans. They also transmit a wide variety of diseases, including tapeworm infections and the typhus-like rickettsiae, causing discomfort to pets (and owners). Adult fleas infest pets; females lay eggs on pet fur. The eggs soon drop from the fur, normally where the pet rests. Larvae are nonparasitic and feed on adult feces, which consists of partially digested blood (Dryden, 2020).
2. Aetiology
2.1 Bacterial characteristics
Fleas (Siphonaptera) are laterally flattened insects. They are about 1–6mm long, depending on the species. The females are bigger than the males. The flea has six legs. The most posterior pair is for jumping. The head of an adult flea has comb-like chitin spines, ctenidiae, which possess useful characters for distinguishing flea species. The eggs have a glossy surface, and their size is about 0.3–0.5mm. The larva is light and vermiform, and its size varies depending on the developmental stage between 4 and 10mm. The size of the cocoon is about 31mm (Saari et al., 2019).
2.2 Classification
3. Epidemiology
3.1 Susceptible hosts
Ctenocephalides species infest carnivores, edentates, lagomorphs, marsupials, primates, rodents and ungulates, and can also be found in the nests, burrows, trails and tracks of their hosts, as well as indoors, where they colonize profusely (Linardi and Guimarães, 2000). Brazilian host species recorded for species of Ctenocephalides include seven orders and 41 species of mammals, as well as one species of bird infested by C. felis felis. Although carnivores can be considered to be the true or primary hosts, infestations on Brazilian carnivores and rodents represent respectively 26.8% and 43.9% of the findings. The cat flea is commonly collected on opossums because of the varied habitats that they use. On the contrary, C. canis is only seen on domestic carnivores (Linardi and Santos, 2012).
3.2 Environment factors
The highest percentage infestations were found in spring, summer, and autumn and were lower in winter. The climatic conditions in the study area and the continuous presence of the hosts favored flea development throughout the year. The environmental conditions in yards and households are important to flea development, and temperature and relative humidity are factors that limit population development. Extreme temperature, >35 or <3°C combined with ≤33% RH reduce flea population development (Harwood and James, 1979; Silverman et al., 1981). In Cuernavaca City, the climatic conditions were uniform throughout the year with a 21.5°C mean temperature in the spring, summer, and autumn and 19.3°C in winter. The relative humidity was ≥60% in all seasons and appeared to provide ideal outdoor environmental conditions for flea development. The health of the domestic pet host is important in flea development, but it is not as important as the outdoor climate throughout the year. The uniform environmental conditions in the area were thought to explain the infestation levels observed throughout the year (Cruz-Vazquez et al., 2001).
4. Life Cycle
Only adult fleas (males as well as females) are parasites. Other stages of the life cycle, comprising about 95% of the flea population, reside in the dog’s living environment, for instance, in the bed. About one-third of a typical adult population consists of males and the other two-thirds are females. Having found a suitable host animal, the fleas usually stay on the same host for the rest of their lives. Adult fleas start sucking blood within a few minutes after finding a suitable host, and egg productions starts about 24–36 h after the first blood meal. Females lay daily dozens of light-colored and glossy eggs among the dog’s hairs (Fig. 2). At first, the surface of the egg is sticky. Once the surface dries, the eggs fall into the environment. The egg hatches to produce a larva (Fig. 2). Hatching takes, depending on the temperature, from less than 2 days to 2 weeks. In dry conditions and in temperatures below 3°C, the development of eggs stops. All life cycle stages are dependent on temperature and humidity. The larva favors conditions where the temperature is 21–32°C and the relative humidity about 70%. It tends to follow gravity and to keep away from light, moving into an optimally sheltered place. The larvae use all sorts of organic material for nutrition, especially the feces of adult fleas, with contains partially digested nutrient rich blood. The larva molts twice before the pupal phase (Fig. 3), which may last from a few weeks up to a year. The actual metamorphosis usually lasts 5– 12days, but before hatching from the pupa, the adult flea awaits signs of the presence of a host animal, for instance trembling, temperature change, or the increase of ambient carbon dioxide concentration. This guarantees a fast blood meal right after hatching. The life cycle of flea is illustrated in Fig. 3. Fleas are not very strict about their host animal. Any suitable species that happens to be available can be a target for a blood meal. Apart from dog and cat fleas, fleas of several wild animal species can cause long-term problems for dogs, when they settle in the dog’s living environment. While bird and hedgehog fleas are common in nature, for instance, they do not usually need to be controlled in dogs, since they stop only briefly for a snack (Saari et al., 2019).
Fleas, like other holometabolous insects, have a four-part life cycle consisting of eggs, larvae, pupae, and adults. Eggs are shed by the female in the environment (1). Eggs hatch into larvae (2) in about 3-4 days and feed on organic debris in the environment. The number of larval instars varies among the species. Larvae eventually form pupae (3), which are in cocoons that are often covered with debris from the environment (sand, pebbles, etc). The larval and pupal stages take about 3-4 weeks to complete. Afterwards, adults hatch from pupae (4) and seek out a warm-blooded host for blood meals. The primary hosts for Ctenocephalides felis and C. canis are cats and dogs, respectively, although other mammals, including humans, may be fed upon. The primary hosts for Xenopsylla cheopis are rodents, especially rats. In North America, plague (Yersinia pestis) is cycled between X. cheopis and prairie dogs. Humans are the primary host for Pulex irritans.
5. Clinical signs and pathology
5.1 Clinical signs
When feeding, fleas inject saliva into the host on which they are living. Many dogs and cats are allergic to flea saliva. Even nonallergic animals will scratch due to the annoyance of flea bites. Allergic dogs itch intensely in some or all areas of the body. They are likely to be restless and uncomfortable, spending much time scratching, licking, rubbing, chewing, and even nibbling at their skin. The classic clinical signs include crusted, itchy skin over the hips, base of the tail, and thighs. This often leads to hair loss, scabbing, and secondary infections. As the disease becomes chronic, hair loss, thickened skin, and darkening of skin color are seen. In heavy infestations (or in young puppies), anemia may develop due to the loss of blood (Dryden, 2020).
Clinical signs of flea infestation can result in direct or indirect signs. Direct signs are attributable directly to the presence of the flea while indirect result from agents carried by fleas – the so-called flea borne diseases.
Direct
When fleas bite, they can cause a range of signs including:
- Mild skin irritation
- Intense itching and biting of skin
- Hair loss
Skin infections (‘hot spots’) – These arise due to the blood sucking behaviour of the flea “injecting in” skin surface bacteria into the animal resulting in a localised skin infection evident in the area around the bite.
Some dogs develop an allergy to the saliva of the flea, this is known as flea allergy dermatitis (FAD). When animals are initially exposed, the immune system develops a hypersensitive response. Once the immune system of these animals is subsequently exposed to more fleas biting, an allergic reaction is triggered. This results in intense itching that lingers long after the flea bite. FAD is commonly associated with hair loss and secondary bacterial infections. Very heavy infestations in young animals can result in excessive blood loss resulting in anaemia and occasionally death (MSD, 2020).
Indirect
Fleas can also transmit bacterial diseases to both animals and humans. Human fleas for example can transmit serious diseases in humans such as Bubonic plague. In Ireland and the UK, dog (and cat) fleas can transmit the tapeworm Dipylidium caninum – known commonly as the dog tapeworm or sometimes even the flea tapeworm. This happens when flea larvae feed on the eggs of this tapeworm. Once swallowed, the tapeworms begin to develop in the gut of the flea into immature forms called cysticercoids. When grooming themselves, dogs and cats may ingest fleas that contain the tapeworm cysticercoids. Inside the digestive tract of dogs and cats the cysticercoids are released and develop into adult tapeworms in the intestine. The same thing can happen in people, for example, if a child happens to swallow an infected flea. Clinical signs associated with this tapeworm include abdominal discomfort, bloating, diarrhea and constipation. Tapeworm infestations can be effectively treated using appropriate anthelmintic products (MSD, 2020).
5.2 Pathology
Parasitic infestations were recorded in many other clinical cases (Fig. 8 & 9). Microscopic examination of skin biopsies showed lymphocytic dermatitis with accumulation of lymphocytes in the dermal layer (Fig. 8.a1), ulceration together with dermal necrosis were also reported necrotic hair follicle (Fig. 8.b2), keratolysis with complete destruction in keratin layer and with swelling in epidermal cells and clear cytoplasm (Fig. 9.a1), and eosinophilic dermatitis with accumulation of eosinophils in the dermal layer (Fig. 9.a2) were recorded. A case of pyodemodicosis was recorded (Fig. 9b) and demodex was appeared by microscopic examination of biopsy (Fig. 9.b1).
6. Diagnosis
Flea infestations and flea allergy dermatitis are definitively diagnosed by observing the fleas on the host's skin. Given that this may be difficult because of the mobility of the flea and the majority of the time it spends off the host, diagnosis is often based on clinical signs, history, and lesion distribution. Sometimes the presence of flea excrement ("flea dirt") on the dog's skin can support a presumptive diagnosis. Circulating eosinophilia is seen in some dogs with flea allergy dermatitis. Differential diagnoses include mite and louse infestations, bacterial folliculitis, and allergic or atopic conditions that present with skin lesions in dogs (e.g., food, drug, or contact hypersensitivity) (Dysko et al., 2002).
7. Treatment
Treatment for fleas needs to address treatment of both the dog and the environment. Many insecticide formulations such as shampoos, sprays, dips, powders, and oral systemics can be used for initial treatment of the individual dog. The active ingredients include pyrethrins, pyrethroids, carbamates, and organophosphates. Flea control in the kennel may need to include outdoor areas in warm climates. Typically, combinations of adult insecticides and juvenile growth regulators are used for environmental treatment. Directed sprays are the most effective means of treating housing areas, because flea “bombs” or foggers do not penetrate adequately into tight areas where fleas might hide.
In addition to insecticide therapy, dogs with flea allergy dermatitis may also require anti-inflammatory medication to relieve clinical signs. Oral prednisone or prednisolone at 0.5 mg/kg q12 hr for 5–7 days has been proposed as a starting therapy. The use of hyposensitization with flea-bite antigens is controversial and not practical for the research setting (Dysko et al., 2002).
THE LIST OF PRODUCT IS RECOMMENDED BY VEMEDIM TO TREAT FLEA AND TICK
| Product Name | Composition | Image |
| ETO MODEX | Afoxolaner……..68mg | |
Fipron…10mg/ml S-Methoprene …….90ml/mL | ||
Imidacloprid………...91 mg Pyriproxyfen…………… 4,6 mg | ||
Fipronil ……..83 mg (S)-methoprene….. 100 mg Eprinomectin….. 4 mg Praziquantel……. 83 mg | ||
Permethrin…….………………..1% Fipronil…….……………….…….0.3% Sodium lauryl sulfate……….10%
| ||
m-phenoxybenzyl - 3- (2,2 dichlorovinyl)-2-2 dymethyl cyclopropanecarboxylate).......1% Sodium Lauryl Sulfate..... 10% | ||
Fipronil …………100mg/mL S-Methoprene …….90ml/mL |
8. Control and prevention
Flea control measures have changed dramatically in recent years. Flea control previously required repeated application of insecticides on the animal and the premises. Recently, new insecticides and insect growth regulators have been developed that provide residual control and require fewer applications. The most effective of these products are sold by veterinarians. Insect growth regulators prevent fleas from reproducing. Flea treatments include topically applied liquids, oral and injected medications, and “fogger” sprays. You should discuss flea control products with your veterinarian and select one that works well for your individual pet and the environment in which it lives.
The goals of flea control are elimination of fleas on pet(s), elimination of existing populations in the environment, and prevention of later infestations of the dog. The first step is to eliminate the existing fleas on the pet. This is necessary to reduce immediate pet discomfort. One common consideration is termed rate or speed of flea kill on a pet. However, it is important to differentiate between speed of elimination of fleas already on the pet and elimination of newly acquired fleas after a product has been applied. When treating a dog with a product applied to the skin externally, it can take up to 36 hours until the medication has spread sufficiently or reached sufficient concentrations to eliminate all existing fleas. If a more rapid rate of kill is needed, a flea spray or one of the new fast-acting oral products may be desirable.
The second step in controlling a flea problem is eliminating fleas in the pet’s environment. In-home studies have shown that in many cases the newer topical and oral flea control products can effectively control flea populations without the need to treat the environment itself. By using these products, it is possible to eliminate a flea infestation in a household; however, the amount of time necessary to achieve flea control will vary because of the flea’s life cycle and conditions in the environment. Typically, control of an infestation can take 6 weeks to 3 months. In cases of massive flea infestation or severe pet or human flea allergy, treatment of the household environment may still be necessary. Wash pet blankets, throw rugs, and pet carriers. Vacuum areas where pets sleep, giving special attention to crevices in sofas and chairs and to areas beneath sofas or beds. Control may be achieved using insecticides with residual activity or by repeated application of short-acting products. Areas where flea eggs and larvae gather, such as bedding, furniture, carpets, the tiny spaces in hardwood flooring, behind baseboards, and within closets, should be treated. In severe infestations, a second treatment may be necessary 7–10 days later.
If your dog spends time outside regularly, also treat the outside areas it frequents. Spraying flea control products over the whole yard is not worthwhile. Instead, concentrate outdoor treatments on shaded areas, including dog houses, garages, under porches, and in animal lounging areas beneath shrubs or other shaded areas. Other outdoor spaces where fleas can be found include cracks in shaded or moist brick walks and patios and areas under decks and steps.
Many pet owners mistakenly think that flea products either kill all newly acquired fleas within seconds to minutes or completely repel them. However, many products do no repel fleas, and long-acting products do not kill most fleas within minutes. Often fleas may live for 6 to 24 hours and bite before being killed. Therefore, close scrutiny of treated pets in an infested environment occasionally results in a few flea sightings on dogs for up to 8 weeks and occasionally longer until the infestation is eliminated.
An additional complication is infestation of the yard by wildlife, feral cats and dogs, or other infested pets. Your own dog may have been treated, but new fleas may be constantly added to your dog's environment by wildlife or feral animals (especially cats). Even when pets go outdoors for only brief periods, they are susceptible to becoming infested. Additionally, people can act as carriers, bringing fleas into the household and infesting unprotected pets.
Despite your best efforts, it may not be possible to totally eliminate fleas rapidly enough to prevent signs of flea allergy dermatitis in your dog. Treatment may also be required to control itching and secondary skin disease in hypersensitive animals. Your veterinarian can prescribe medications to control your dog’s skin condition and make your pet more comfortable (Dryden, 2020).
9. References
Fouda, M., Abdel-Saeed, H., Abdelgayed, S., Abdou, O., 2021. Clinical, haemato-biochemical, and histopathological studies on some dermopathies in dogs. Advances in Animal and Veterinary Sciences 9, 94-102.
CDC, 2017. Ctenocephalides canis, Ctenocephalides felis.
Coyner, K.S., 2019. Clinical atlas of canine and feline dermatology. John Wiley & Sons.
Cruz-Vazquez, C., Gamez, E.C., Fernandez, M.P., Parra, M.R., 2001. Seasonal Occurrence of Ctenocephalides felis felis and Ctenocephalides canis (Siphonaptera:Pulicidae) Infesting Dogs and Cats in an Urban Area in Cuernavaca, Mexico. Journal of Medical Entomology 38, 111-113.
Dryden, M.W., 2020. Fleas of Dogs. MSD manual Veterinary Manual.
Dysko, R.C., Nemzek, J.A., Levin, S.I., DeMarco, G.J., Moalli, M.R., 2002. Chapter 11 - biology and diseases of dogs, in: Fox, J.G., Anderson, L.C., Loew, F.M., Quimby, F.W. (Eds.), Laboratory Animal Medicine (Second Edition). Academic Press, Burlington, pp. 395-458.
Harwood, R.F., James, M.T., 1979. Entomology in human and animal health. Macmillan Publishing Co. Inc. New York; Baillière Tindall, 35 Red Lion.
Kaufman, K.R.S.a.P.E., 2020. Ctenocephalides canis (Curtis) (Insecta: Siphonaptera: Pulicidae), Entomology and Nematology Department University of Florida.
Linardi, P.M., Guimarães, L.R., 2000. Sifonápteros do Brasil, Sifonápteros do Brasil, pp. x, 291-x, 291.
Linardi, P.M., Santos, J.L.C., 2012. Ctenocephalides felis felis vs. Ctenocephalides canis (Siphonaptera: Pulicidae): some issues in correctly identify these species. Revista brasileira de parasitologia veterinária 21, 345-354.
MSD, 2020. Fleas on dogs. MSD Animal Health Republic of Ireland.
Saari, S., Näreaho, A., Nikander, S., 2019. Chapter 8 - Insecta, in: Saari, S., Näreaho, A., Nikander, S. (Eds.), Canine Parasites and Parasitic Diseases. Academic Press, pp. 159-185.
Silverman, J., Rust, M.K., Reierson, D.A., 1981. Influence of temperature and humidity on survival and development of the cat flea, Ctenocephalides felis (Siphonaptera: Pulicidae). Journal of Medical Entomology 18, 78-83.
