Scabies is caused by the mite Sarcoptes scabies, variety hominis. The characteristic symptoms of scabies infection include superficial burrows, intense pruritus, a generalized rash and secondary infection. S-shaped tracks in the skin are often accompanied by small, insect-type bites called nodules that may look like pimples. These burrows and nodules are mostly located in the crevices of the body, such as the webs of fingers, toes, feet, buttocks, elbows, waist area, genital area and axilla. The intense itching and rash is caused by an allergic reaction to the mites and their by-products under the skin that develops over time. The rash can be found over much of the body, especially in immune-compromised subjects; the associated itching is often most prevalent at night. Secondary impetigo may occur after scratching (Figure 31).
Figure 31. Scabies.
In individuals who have never previously been exposed to scabies, the onset of clinical signs and symptoms is 2–6 weeks after infestation. In previously exposed individuals, onset can be as soon as 1–4 days after infestation.
Scabies is highly contagious and can be spread by scratching, picking up the mites under the fingernails and touching another person's skin. They can also be spread onto other objects like keyboards, toilets, clothing, towels, bedding, and furniture onto which the mite may be rubbed off, especially if a person is heavily infested. Crowded facilities on board may favour the transmission of scabies throughout an entire crew by skin-to-skin contact with an infected person. Transmission is also likely between bed partners. The parasite mostly does not survive longer than two or three days away from human skin.
Generally, the diagnosis is made by the identification of burrows (Figure 31). This may be difficult because they are scarce and obscured by scratch marks. If burrows are not found in the primary areas that are likely to be affected, the entire skin surface of the body should be examined.
Topical permethrin 5% is the drug of choice and is applied to the skin before bedtime and left on for about 8 to 14 hours, then showered off in the morning. There is some evidence that a 10% sulphur ointment in petroleum jelly applied topically is effective. It is cheap and readily available without a prescription.
An outbreak on board a ship should focus on preventing re-infection. All close contacts should be treated at the same time, even if asymptomatic. Cleaning of the environment should occur simultaneously and include treatment of furniture and bedding, vacuuming floors, carpets and rugs, mopping and disinfecting floor and bathroom surfaces by mopping, cleaning the shower after each use. Daily washing in hot water of recently worn clothes, towels and bedding and then drying in high heat and/or steam ironing will help prevent transmission. Permethrin sprays can be used for items that cannot be laundered.
Pediculosis is an infestation of lice – blood-feeding ectoparasites. "Pediculosis" in humans refers to lice infestation of any part of the body, and may be divided into the following types: Pediculosis capitis, Pediculosis corporis and Pediculosis pubis (crabs).
Head lice. Infestation with P. humanus capitis is most frequent on children and their families. Lice are spread through direct head-to-head contact with an infested person. From each egg or "nit" may hatch one nymph that will grow and develop to the adult louse. While feeding on blood by piercing the skin with their mouthparts their saliva irritates the skin and causes itching.
To diagnose infestation, the entire scalp should be combed thoroughly with a louse comb and the teeth of the comb should be examined for the presence of living lice after each time the comb passes through the hair.
There are a number of treatment modalities such as combing, shaving, hot air or pediculocide that can be employed but none of these assures 100% destruction of the eggs and hatched lice after a single treatment.
Body lice. P. humanus humanus (the body louse) is indistinguishable in appearance from the head louse but body lice attach their eggs to clothes, whereas head lice attach their eggs to the base of hairs.
Body lice infestations can spread rapidly under crowded living conditions with poor hygiene but is unlikely to persist on anyone who bathes regularly and who has at least weekly access to freshly laundered clothing and bedding.
Body lice are spread through prolonged direct physical contact with an infested person or through contact with clothing, beds, bed linens, or towels that have been in contact with an infested person. Body lice are a nuisance in themselves and cause intense itching. They are however, also vectors of other diseases (epidemic typhus, trench fever, and louse-borne relapsing fever).
Nits (eggs) are generally easy to see in the seams of an infested person’s clothing, particularly around the waistline and under armpits. They are oval and usually yellow to white in colour. The nits may take 1-2 weeks to hatch.
A body lice infestation is treated by improved personal hygiene. A pediculicide is generally not necessary if hygiene is maintained and items such as clothing, bedding, and towels used by the infested person are laundered in hot water at least once a week.
Pubic lice (Phthiriasis pubis – also known as "crabs") are parasitic insects that infest human genitals but they may also live on other areas with hair, including the eyelashes. They feed exclusively on blood (Figure 32).
Figure 32. Crab lice.
The main symptom is itching in the pubic-hair area, resulting from hypersensitivity to louse saliva, which can become stronger over two or more weeks following initial infestation. In some infestations, a characteristic grey-blue or slate coloration appears (maculae caeruleae) at the feeding site, which may last for days. A pubic louse infestation is usually diagnosed by carefully examining pubic hair for nits, nymphs’ nits, and adult lice.
Pubic lice usually infect a new host only by close contact between individuals, usually through sexual intercourse. As with most sexually transmitted pathogens, they can only survive a short time away from the warmth and humidity of the human body.
Because of the strong association between the presence of pubic lice and classic sexually transmitted infections, patients diagnosed with pubic lice should undergo evaluation for other sexually transmitted diseases.
Pubic lice can be treated by applying Permethrin 1% cream rinse or pyrethrins to the affected areas. Shaving off or grooming any hair in the affected areas with a fine-toothed comb is necessary to ensure full removal of the dead lice and nits. A second treatment after 10 days is recommended. Bed sheets should be changed and be put away in a plastic bag, without air and well shut. They should be left alone for 15 days before washing to avoid the reproduction and survival of lice eggs that may have been left on the sheets and lead to reinfestation.
Cockroaches are frequent type 1 sensitizer in ships, especially those sailing in the tropics. In addition to airways symptoms they may be related to dermatitis.34 The clinical significance remains unclear.