Flea infestation: a snapshot on the common products and the reasons for treatment failure

With impressive reproductive capabilities, ability to persist in the environment and as pathogenic vectors, fleas are considered to be the most important ectoparasite of dogs and cats (Abdullah et al, 2019). Of the 2500 species worldwide, Ctenocephalides felis (cat flea), Ctenocephalides canis, Pulex simulans and Echidnophaga gallinacea are seen as significant, because of their ability to infest companion animals in large numbers (Blagburn and Dryden, 2009). Among the species mentioned above, the cat flea is the most dominant species affecting cats and dogs. Most investigations that have been carried out focus on this species, therefore the following discussion will be largely limited to the cat flea.

Fleas are laterally flattened, dark brown insects around 2–5 mm in size. Although fleas are wingless (Figure 1), they are highly mobile because of their strong hind legs adapted for jumping (Wright and Elsheikha, 2014). Adult fleas are obligate blood-feeders. Once a host is found, feeding can occur within minutes, subsequently followed by mating. Egg production then begins within 24 to 36 hours of the first blood meal, with up to 50 eggs being laid per egg laying adult female per day. As the eggs are non-adhesive, host movement causes eggs to fall into the environment. Eggs hatch into larvae within 1 to 10 days (Blagburn and Dryden, 2009). Larvae must feed on the blood-rich faeces of adult fleas, known as ‘flea dirt’, in order to successfully undergo two moults and enter the pupal stage (Figure 2). The third stage larvae spin a sticky cocoon covered in environmental debris, in which they moult into flea pupae and mature into adult fleas (Dobler and Pfeffer, 2011). The pre-emerged adults can remain dormant for several months until stimulated by vibrations, carbon dioxide and/or heat. Under most household conditions, the lifecycle is completed within 3 to 8 weeks, but can extend up to 174 days depending on environmental conditions (Blagburn and Dryden, 2009). Colder temperatures in winter can kill off fleas and immature stages residing outdoors. However, fleas inside the home will survive (Beugnet et al, 2004). Fleas are ubiquitous and exposure to flea infestation is hard to avoid. Companion animals that are kept indoors still require treatment as fleas can be brought into the home by other animals or on the owner's clothing. As a result, both the European Scientific Counsel of Companion Animal Parasites (ESCCAP) and the Companion Animal Parasite Council (CAPC, 2020) recommend all year round protection against fleas.