Editing Yaws (section)

==Diagnosis==
[[File:Psoriasiform epidermal hyperplasia and band-like lymphocytic infiltrates in papillary dermis.jpg|thumb|Lesion biopsy under a microscope, clear [[epidermal hyperplasia]]]]
{{Multiple image
| width =
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| image1 = 10.1177 0956462414549036-fig6-Secondary yaws- dactylitis.jpg
| alt1 = An irregularly-thickened first finger; proximal fingerbone is asymmetrically swollen
| caption1 = Dactylitis of secondary yaws due to periostitis
| image2 = 10.1177 0956462414549036-fig7-Secondary yaws- radiographic evidence of osteoperiostitis.jpg
| alt2 = radiograph showing the same hand with thickened bones
| caption2 =  Periostitis of secondary yaws may be visible on an X-ray, even if not otherwise visible<ref name=yaws/>
}}
Most often, the diagnosis is made clinically.<ref name=MedicineNet/> [[Dark field microscopy]] of samples taken from early lesions (particularly ulcerative lesions<ref name=MedicineNet/>{{verify source|date=April 2020}}) may show the responsible bacteria; the [[spirochaetes]] are only 0.3 μm wide by 6–20 μm long, so light-field microscopy does not suffice.<ref name=yaws/>

A microscopic examination of a biopsy of a yaw may show skin with clear [[epidermal hyperplasia]] (a type of skin thickening) and [[papillomatosis]] (a type of surface irregularity), often with focal [[spongiosis]] (an accumulation of fluid in a specific part of the epidermis). [[Immune system]] cells, [[neutrophil]]s and [[plasma cell]]s, accumulate in the skin, in densities that may cause microabscesses.{{citation needed|date=January 2021}}

[[Warthin–Starry stain|Warthin–Starry]] or Levaditi silver stains selectively stain ''T. pallidum'', and direct and indirect [[immunofluorescence]] and [[immunoperoxidase]] tests can detect [[polyclonal antibodies]] to ''T. pallidum''{{'s}}. Histology often shows some spatial features that distinguish yaws from syphilis (syphilis is more likely to be found in the dermis, not the epidermis, and shows more [[endothelial cell]] proliferation and [[blood vessel|vascular]] obliteration).<ref name=yaws/>

[[Serological testing|Blood-serum (serological) tests]] are increasingly done at the point of care. They include a growing range of [[treponemal]] and nontreponemal assays. Treponemal tests are more [[specificity (statistics)|specific]], and are positive for anyone who has ever been infected with yaws; they include the [[TPHA|''Treponema pallidum'' particle agglutination assay]]. Nontreponemal assays can be used to indicate the progress of an infection and a cure, and positive results weaken and may become negative after recovery, especially after a case is treated early.<ref name=advances/> They include the venereal disease research laboratory ([[VDRL]]; requires microscopy) and rapid plasma {{Not a typo|reagin}} ([[Rapid Plasma Reagin|RPR]]; naked-eye result) tests, both of which [[flocculate]] patient-derived [[antibodies]] with [[antigens]].<ref name=yaws/>

Serological tests cannot distinguish yaws from the closely related [[syphilis]];<ref name=yaws/> no test distinguishing yaws from syphilis is widely available. The two genomes differ by about 0.2%. [[Polymerase chain reaction|PCR]] and [[DNA sequencing]] can distinguish the two.<ref name=yaws/> There are also no common blood tests that distinguish among the four [[treponematosis|treponematoses]]: syphilis (''T. p. pallidum''), yaws (''T. p. pertenue''), bejel (''T. p. endemicum''), and pinta (''T. carateum'').<ref name=MedicineNet/>

''[[Haemophilus ducreyi]]'' infections can cause skin conditions that mimic primary yaws. People infected with ''Haemophilus ducreyi'' lesions may or may not also have latent yaws, and thus may or may not test positive on serological tests. This was discovered in the mid-2010s.<ref name=advances/> It seems that a recently diverged strain of ''Haemophilus ducreyi'' has evolved from being a sexually transmitted infection to being a skin ulcer pathogen that looks like yaws.<ref>{{cite journal |last1=Lewis |first1=David A. |last2=Mitjà |first2=Oriol |title=Haemophilus ducreyi: from sexually transmitted infection to skin ulcer pathogen |journal=Current Opinion in Infectious Diseases |date=February 2016 |volume=29 |issue=1 |pages=52–57 |issn=1473-6527 |pmid=26658654 |doi=10.1097/QCO.0000000000000226 |s2cid=1699547}}</ref>

Yaws has been reported in nonendemic countries.<ref name=yaws/>