Immediate antibody-mediated allergic reactions (wheals) have been elicited in infected persons, but not in healthy persons; immediate hypersensitivity of this type is thought to explain the observed far more rapid allergic skin response to reinfection seen in persons having been previously infected (especially having been infected within the previous year or two). Transmission
Scabies is contagious and can be contracted through prolonged physical contact with an infested person. This includes sexual intercourse, although a majority of cases are acquired through other forms of skin-to-skin contact. Less commonly, scabies infestation can happen through the sharing of clothes, towels, and bedding, but this is not a major mode of transmission; individual mites can survive for only two to three days, at most, away from human skin at room temperature. As with lice, a latex condom is ineffective against scabies transmission during intercourse, because mites typically migrate from one individual to the next at sites other than the sex organs.Healthcare workers are at risk of contracting scabies from patients, because they may be in extended contact with them. Pathophysiology
The symptoms are caused by an allergic reaction of the hosts body to mite proteins, though exactly which proteins remains a topic of study. The mite proteins are also present from the gut, in mite feces, which are deposited under the skin. The allergic reaction is both of the delayed (cell-mediated) and immediate (antibody-mediated) type, and involves IgE (antibodies are presumed to mediate the very rapid symptoms on reinfection).
Negative results may prompt retesting in the future to rule out early sampling of blood serum. A positive result can also be indicative of an infection within the past two to six months. People acquire lifetime immunity if IgG antibodies are produced in response to parvovirus B19 exposure. Infection by parvovirus B19 can also be confirmed by isolation of viral DNA detected by PCR or direct hybridization. PCR Is considered significantly more sensitive to detecting viral antigen compared direct DNA hybridization. DNA hybridization assay can better detect variants of the parvovirus B19. There exists 3 biological similar genotypes of parvovirus B19, numbered one through three. The most common genotype circulating is genotype one. Laboratory tests can indicate complications of infection, including anemia, liver damage, and low platelet count. Transmission
Fifth disease is transmitted primarily by respiratory secretions (saliva, mucus, etc. ), but can also be spread by contact with infected blood. The incubation period (the time between the initial infection and the onset of symptoms) is usually between 4 and 21 days. Individuals with fifth disease are most infectious before the onset of symptoms. Typically, school children, day-care workers, teachers, and parents are most likely to be exposed to the virus. When symptoms are evident, the risk of transmission is small; therefore, symptomatic individuals do not need to be isolated. Vertical transmission from maternal infection may also occur, which can lead to hydrops fetalis due to the infections detrimental effects on red blood cell production. Treatment
Treatment is supportive, as the infection is frequently self-limiting.