PARASITES

In the UK, the parasites most commonly causing infestation are:

• Head lice (Pediculosis capita - infestation)
• Pubic lice (pediculosis pubis, infestation caused by pthirus pubis)
• Scabies mites (Sarcoptes scabiei)
• Threadworms (Enterobius vermicularis)

HEAD LICE (Pediculosis capita)

Head lice (Pediculosis capita) are tiny (up to 3 mm), tan/grey-white/black wingless insects that cling to hairs and suck blood from the scalp. Female lice glue their eggs to the base of hair shafts. Eggs hatch to leave empty white shells (‘nits’) stuck tightly to the hair, not easily brushed out. Adult lice walk from one head to another during close head-to-head contact. They can infect anyone with hair but most often children aged 4–11 years. Infection (usually with <12 lice) is normally asymptomatic. Lice can be detected and removed with a special fine-tooth comb after washing hair and applying a generous amount of ordinary conditioner. 

Pubic lice (Pediculosis pubis, ‘crabs’)

Tiny (up to 3 mm), grey-brown blood-sucking insects that live in coarse human body hair, most commonly pubic hair (but also eyelashes/brows, beards/moustaches, hair on abdomen or back) and cause itching and red spots. Females lay eggs as head lice (see in Parasites). Pubic lice do not wash or brush off with normal bathing with soap and water. Spread by sexual contact.

Scabies (Sarcoptes scabiei var. hominis)

Microscopic mite causing a contagious, intensely itchy skin condition. Presents with itchy papular rash (on abdomen or thigh, itch most intense at night), and burrows (tiny grey irregular tracks) in digital web spaces and on flexor wrist surfaces. Typically, infestation is with 10-12 adult mites. Scabies can affect children, young adults and the elderly in every community. Spread is by skin-to-skin contact so occurs readily in families. Crusted or ‘Norwegian’ scabies is a highly contagious variant in which there are thousands or even millions of mites but little itch; this is the usual cause of severe outbreaks of scabies in institutions, e.g. nursing homes, prisons.

Threadworm (Enterobius vermicularis)

Adult worms (white and a few mm long), live in the caecum. Females migrate to the anus to lay eggs, usually at night, causing night-time itching (pruritus ani). Threadworms are more common in school or pre-school children than in adults, but can affect whole families, especially in overcrowded conditions. Diagnose infection by applying adhesive tape to the anus; microscopy will reveal typical eggs. Treatment with an antihelmitic is available from pharmacies. Important to treat the whole family (even if asymptomatic) and follow stringent hygiene measures to ensure eradication. Exclusion from school of affected children is unnecessary.