Cercarial dermatitis is an uncomfortable, but not life-threatening rash,
the severity of which can range from a nuisance to interfering with normal
activities. Minutes to hours after contact with cercariae infested water,
a person may experience a prickling sensation or itchiness where cercariae
penetrate the skin. Within 12 to 24 hours, a macular rash develops on the
skin that was exposed to the water. Erythema (reddening of the skin) or
urticaria may develop during this time. Next, the rash proceeds to
maculopapular eruptions and may develop purpurtic lesions. The rash then
proceeds to a vesicular state. Often times, intense itchiness causes
people to scratch, leading to ulceration of the vesicles. The rash may be
further complicated by secondary bacterial infection.
It is important to note that although human Schistosomiasis can cause a
rash, it is not as severe and noticeable as that caused by avian or bovine
cercariae. It has been reported that the cercariae S. masoni produces an
anti-inflammatory agent that is absent in avian cercariae. One can
speculate that the absence of this agent may contribute to the severity of
the immune response that leads to cercarial dermatitis. The severity of
the dermatitis is conditional upon several factors:
Length of time in water: The longer a person spends in
contaminated water, the higher the chances that the cercariae will
penetrate the skin. Futhermore, the longer a person is exposed to water,
the more times the skin is penetrated.
Drying off after being in the water: Drying off immediately
after one gets out of the water removes any cercariae on the surface of
the skin that may attempt to enter the skin.
Previous exposure: The maculopapular rash that characterizes
cercarial dermatitis is essentially an immune response to the presence of
the cercariae. The first exposure to cercariae produces a primary immune
response, so the response may take longer to manifest into a rash.
However, subsequent exposures lead to faster and more vigorous immune
responses, leading to more pronounced symptoms. For example, in the early
20c. the Japanese koganbyo (lake side disease), which was common in
the rice-growing district of Shinji Lake. Rice growing requires
continuous labor in flooded fields, hence rice farmers are very vulnerable
to cercarial dermatitis. Koganbyo is an extreme form of cercarial
dermatitis leading such severe itching that it caused insomnia, extensive
papules, swollen axillary or inguinal lymph glands and sloughing off of
skin.
courtesy of Hope
University
Diagnostic Tests
There are no readily available and easy tests for cercarial dermatitis.
Diagnosis is based on a history of exposure to water that may be
contaminated with cercariae. Other diagnostic methods used are capturing
snails in areas where an outbreak occurs and testing their secretions to
see if any cercariae are present. This, however, takes time. A quicker
way to accomplish this is to crush snails and examine the remains for
cercariae. Basically the most common methods for diagnosis require
visualization of the cercariae using microscopy. During the early 20th
century there was a skin test developed using parts of cercariae.
However, the reaction to the skin test was very vigorous. This does not
make sense to use for a disease that is self-limiting and not life
threatening. Needless to say the skin test is not currently used to
diagnose cercarial dermatitis.
Management & Therapy
Since cercarial dermatitis usually resolves by itself in 2-3 days,
management involves symptomatic treatment. Topical anti-itch creams and
antihistamines can help alleviate the intense itching that develops. For
more severe cases, mild topical corticosteriods can help dampen the immune
response and alleviate the rash. Home remedies such as cool compresses and
bathing with baking soda are also recommended.
