Lesion biopsy under a microscope, clear epidermal hyperplasia Most often the diagnosis is made clinically. Dark field microscopy of samples taken from early lesions (particularly ulcerative lesions) 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. 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 specific part of the epidermis). Immune system cells, neutrophils and plasma cells, accumulate in the skin, in densities that may cause microabscesses. Warthin–Starry or Levaditi silver stains selectively stain T. pallidum, and direct and indirect immunofluorescence and immunoperoxidase tests can detect polyclonal antibodies to T. pallidums. Histology often shows some spatial features which distinguish<unk>  from syphilis (syphilis is more likely to be found in the dermis, not the epidermis, and shows more endothelial cell proliferation and vascular obliteration). 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 specific, and are positive for any one who has ever been infected with<unk> ; they include the 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 treated early. They include the venereal disease research laboratory (VDRL; requires microscopy) and rapid plasma (RPR; naked-eye result) tests, both of which flocculate patient-derived antibodies with antigens. Serological tests cannot distinguish<unk>  from the closely related syphilis; no test distinguishing<unk>  from syphilis is widely available. The two genomes differ by about 0.2%. PCR and DNA sequencing can distinguish the two. There are also no common blood tests which distinguish among the four treponematoses: syphilis (Treponema pallidum pallidum),<unk>  (Treponema pallidum pertenue), bejel (Treponema pallidum endemicum), and pinta (Treponema carateum). Haemophilus ducreyi infections can cause skin conditions that mimic primary<unk> . People infected with Haemophilus ducreyi lesions may or may not also have latent<unk> , and thus may or may not test positive on serological tests. This was discovered in the mid 2010s. 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<unk> .<unk>  has been reported in nonendemic countries.
Yaws
Enanthem
Scrubs 
Exanthem
Chilblains
Tuberculosis hut
Scabies
Saddle sore