Fleas

Ctenophalides Species

• Felis species- widespread.
• Canis species- host restricted. 
• Spilopsyllus Cuniculi- rabbit flea. 

Fleas have a holometabolous life cycle which means that the larvae resemble maggots for a better term, and do not resemble the adult like in ticks which are described as nymphal stages. 

The adult stage is the only stage which exists on the host and is parasitic. This accounts for only 5% of the lifecycle. 

1. Pupae- stimulus for hatching is carbon dioxide, vibrations and warmth. Rapid numbers under optimal conditions. Also affected by humidity which should be above 70%. Most of the life cycle is off the host. Temperatures below freezing means the fleas die off. 
2. Adults feed on blood of the host. Cat fleas are polyxenous which means they can infect multiple hosts. 
3. Eggs are always laid in the environment. They take between days and weeks to hatch depending on conditions. At 30 degrees the eggs take three weeks to hatch and develop into the adult, whereas at 15 degrees they take 3 months from an egg to adult. 
4. Three larval instars as larvae. Feed on 'flea dirt.' The black stuff you find on the dogs coat if they have fleas. 
5. Pupae- wooly. Development can be as short as 10 days or as long as a year depending on conditions. This is known as the 'pupal window' and is the source of constant reinfection. 

Pathogenesis

• Irritation due to the blood feed and their movement.
• Flea Allergic Dermatitis (known as miliary dermatitis in the cat)- allergen in the flea saliva. Presents as alopecia and papules. 
• The flea is the intermediate host for dipylidium caninum tapeworm discussed in an earlier blog. 

Control 

Several drugs kill fleas which are on the dog, these are known as adulticides and include fipronil, imidacloprid and selamectin. Other drugs are used in the environment or are given as a further preventative measure. These are either:

1. Insect growth regulators- lufenuron blocks chitin synthesis in the eggs. This is given as an injection or tablet to the dog, and is in the drug 'program.' 
2. Juvenile hormone analogues- methoprene and pyriproxyfen which stop hormonal development in the egg. These are found in household flea sprays for the environment to prevent pupal window reinfection.