Orf virus is a
DNA parapoxvirus that causes orf
(ecthyma contagiosum)
, an acute debilitating skin disease of sheep, goats and humans.
Orf (ecthyma contagiosum) usually
causes crusted lesions on the lips and perioral area.
Visit:
Variola (smallpox) ;
Molluscum Contagiosum
;
Herpes Virus(Herpesviridae)
Mode of infection:
Orf can be transmitted to humans by contact with infected animals. In
some cases the lesion developed at sites of trauma produced by an
inanimate object.
Site:
It occurs most
commonly on the index finger. The.lesions
(about 1-3 cm or more in diameter) are usually located on the hands
and forearms. Other sites include the face, scalp, temple, and
perianal region.
Clinical presentation:
Several lesions may be present in the one area. A mature lesion
is nodular with central umbilication and an erythematous halo.
Complications:
The characteristic lesion resembles a tumour and resolves
spontaneously (after
about 7 weeks)
, usually without any complications. However, rare complications such
as lymphangitis, adenitis, erythema multiforme,
toxic erythema
, erysipelas, papulovesicular eruption . Pseudomonas aeruginosa
infection, and bullous pemphigoid have been reported. In one case
giant orf caused swan-neck deformity and paresthesia.
Recurrent lesions have
been reported in immunocompromised persons.
The features depend on the stage of the
disease.
Early lesions :
- Moderate epidermal acanthosis ;
- Pale vacuolated cytoplasm, mainly in
the upper epidermis ;
- Cytoplasmic inclusion bodies are
usually present;
- ‘Spongiform degeneration’ -
vacuolated cells having wispy strands of eosinophilic cytoplasm.
Usually seen in follicular structures.
- Intraepidermal vesicles or bullae may
form.
- Dilated thin-walled vessels and an
infiltrate of lymphocytes, macrophages and occasional eosinophils and
plasma cells in the dermis
Later lesions:
- Epidermal necrosis, mainly in the
center.
- Neutrophils are often present within
and close to the necrotic epidermis.
- Other biopsies may show elongated
rete pegs with dilated vessels in the intervening dermal papillae.
- Sometimes there is an unusual
proliferation of endothelial cells in the dermal papillae . This
feature may resemble a vascular tumour.
- The inflammatory infiltrate and
epithelial hyperplasia finally resolve.
Differential diagnosis:
Milker’s nodules : It
is difficult to distinguish between the lesions of orf from
milker’s nodules. Full-thickness epidermal necrosis seems to be more
common in orf.
Diagnosis:
Immunoperoxidase techniques
using orf-specific monoclonal antibodies can be used to confirm the
diagnosis.
This zoonotic
infection shares clinical manifestations and exposure risks with
other, potentially life-threatening zoonoses (Eg.cutaneous
anthrax)
and is likely under-recognized because of a lack of clinical suspicion
and widely available diagnostics. Barrier precautions and proper
hand hygiene are recommended for the prevention of orf virus infection
in humans.
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