Yaws: Symptoms, Causes & Treatment | aihealz

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Yaws: Symptoms, Causes & Treatment | aihealz | aihealz

§ 02

How you might notice it

01A single painless raspberry-like papilloma (the mother yaw), 1-5 cm wide, appearing at the site of skin contact 9-90 days after exposure — most often on the leg, foot, or buttock.

02Multiple smaller papillomas spreading across the trunk and limbs weeks to months later, sometimes coalescing into ulcerated plaques.

03Painful thickening and cracking of the soles (plantar hyperkeratosis, called 'crab yaws'), making walking on the heels characteristic and the source of the historical name.

04Deep bone pain in the long bones (tibia, ulna, fingers), worse at night, due to periostitis and osteitis from spirochete invasion.

05Regional lymphadenopathy near the primary lesion, with rubbery non-tender nodes 1-2 cm in diameter.

06Saber-shaped bowing of the tibia (saber tibia) developing over years of untreated infection due to chronic periosteal thickening.

07Disfiguring destruction of the nose, palate, and central face called gangosa, occurring in late tertiary disease after 5-10 years untreated.

08Juxta-articular subcutaneous nodes — firm rubbery nodules near elbows, knees, and other large joints — a hallmark of tertiary yaws.

09Hyperpigmented or hypopigmented patches at the sites of healed lesions, often persisting for years.

10General constitutional symptoms during secondary disease including malaise, low-grade fever, and headache.

early warning signs

•A new, painless, slowly-growing papilloma on a child's leg or foot in a yaws-endemic area
•Living in or recent travel to West/Central Africa, Pacific Islands, Papua New Guinea, the Solomon Islands, or rural Indonesia
•Multiple skin lesions appearing on a child after another household contact has had yaws
•Painful soles and difficulty walking on flat ground in a school-age child in an endemic community

● emergency signs

•Rapidly destructive facial lesions involving nose, mouth, or palate — late gangosa requires urgent referral and may indicate co-infection
•Secondary bacterial infection of yaws ulcers causing fever, surrounding cellulitis, and rapid expansion — needs systemic antibiotics
•Septic arthritis of a joint adjacent to a yaws lesion in a child — requires aspiration and culture
•Severe Jarisch-Herxheimer-like reaction after azithromycin in a child with very high spirochete burden — supportive care needed

§ 03

How it’s diagnosed

diagnosis

Diagnosis combines clinical recognition of a characteristic lesion in an endemic-area child with serologic confirmation. The WHO operational case definition for surveillance is: a person living in an endemic area with one or more typical papilloma or ulcer plus a positive rapid treponemal test. Direct dark-field microscopy of papilloma fluid can show motile spirochetes, but the test is logistically difficult in field settings. Serology is the practical mainstay. Two complementary tests are used: a treponemal test (rapid TPHA or DPP Syphilis Screen and Confirm) detects antibodies that persist for life and confirms exposure, and a non-treponemal test (RPR or VDRL) measures active disease and reverts to negative or low titer after successful treatment. A fourfold drop in RPR titer at 6 months is the cure marker. PCR testing for T. pallidum DNA on lesion swabs is the most specific tool and is the reference method in WHO eradication trials — it can also detect the macrolide-resistance 23S rRNA mutation that emerged after a 2018 outbreak in Papua New Guinea. Skeletal X-ray shows periosteal thickening of the tibia and ulna in advanced disease. The key clinical distinction is from venereal syphilis, which is serologically indistinguishable. In a child under 15 in an endemic area with no sexual history, positive treponemal serology essentially confirms yaws.

Key tests

Rapid treponemal test (DPP Syphilis Screen and Confirm)First-line field test that detects both treponemal and non-treponemal antibodies on one cassette from a finger-prick sample. Used by WHO for mass screening during eradication campaigns.

Rapid Plasma Reagin (RPR) or VDRL titerQuantifies active infection and tracks treatment response. A fourfold (two-tube) drop in titer at 6 months post-treatment is the cure criterion.

T. pallidum Particle Agglutination (TPPA) or Treponema pallidum Hemagglutination (TPHA)Confirmatory treponemal test that distinguishes treponemal infection from false-positive RPR. Remains positive for life regardless of treatment.

Dark-field microscopy of lesion exudateDemonstrates motile spirochetes from active papillomata under specialized lighting. Highly specific but requires a fresh sample and trained operator.

PCR for T. pallidum DNAReference standard for confirmation and the only test that can detect the 23S rRNA macrolide-resistance mutation. Used in WHO surveillance and outbreak investigations.

Plain X-ray of long bonesIdentifies periosteal thickening (saber tibia), osteitis of fingers and ulnae, and gummatous bone destruction in tertiary disease.

Outlook

With timely treatment, the prognosis is excellent. A single oral dose of azithromycin cures over 95% of patients, lesions heal within 4-8 weeks, and RPR titers fall fourfold or more in over 90% of cured patients by 6 months. Permanent disfigurement and bone deformity occur only after 5-10 years of untreated infection and are now rare in surveillance-era countries. Sequelae of childhood untreated infection — saber tibia, gangosa, juxta-articular nodes — are essentially irreversible without reconstructive surgery, though active disease and pain resolve with antibiotics at any stage. Mortality from yaws itself is extremely low; the historical burden was almost entirely morbidity from disfigurement, school absence, and stigma. The 2018 emergence of azithromycin-resistant strains in Papua New Guinea is a concern but has not yet derailed eradication efforts, as benzathine penicillin remains universally effective.

§ 05

Causes & risk factors

known causes

Infection with Treponema pallidum subsp. pertenue: The spirochete bacterium responsible for yaws. Morphologically and genetically near-identical to T. pallidum pallidum (the syphilis pathogen), differing by approximately 0.2% at the genomic level, but biologically restricted to skin and bone in temperate-to-tropical climates.
Direct skin-to-skin transmission through minor abrasions: The bacterium enters through small cuts, scratches, insect bites, or eczema. Children playing in close contact in endemic communities transmit it efficiently. There is no sexual or congenital transmission.
Warm, humid climate above 27°C average temperature: T. pertenue requires sustained skin moisture to survive briefly outside the host. Endemic transmission is confined to tropical lowland regions with high humidity and rainfall above 1,250 mm annually.
Crowded living conditions with limited access to water and soap: Communities without reliable handwashing facilities, where children share bedding and play closely, have much higher transmission. Improved hygiene alone reduces incidence by 30-50% even without antibiotic mass treatment.
Untreated household contacts as reservoirs: A single untreated person with secondary lesions can infect multiple children in their household. This is why WHO eradication strategy targets community-wide treatment rather than individual cases.

risk factors

Age 2-15 yearsnon-modifiable: Children in this age band account for 75-80% of cases due to closer skin contact during play, more frequent skin breaks, and lack of acquired immunity from prior exposure.
Living in a tropical endemic regionenvironmental: West and Central Africa, Papua New Guinea, Solomon Islands, rural Indonesia, and parts of Southeast Asia carry essentially all current cases. Travel-acquired yaws is rare.
Poverty and lack of access to soap and clean watermodifiable: Communities without reliable hygiene supplies have 3-5 fold higher attack rates. Improved water access measurably reduces incidence.
Crowded household contacts with active casesmodifiable: Household contacts of an active case have a 10-20% probability of acquiring the infection over the following 6 months without intervention.
Skin abrasions, eczema, or insect bitesmodifiable: Any break in the skin barrier facilitates entry. Children with chronic skin conditions or frequent minor injuries from playing barefoot are at elevated risk.
Male sex (slight)non-modifiable: Some studies report a slight male predominance (~1.2-1.5x) likely reflecting outdoor activity patterns rather than biological susceptibility.

§ 08

Frequently asked

Is yaws still around today?

Yes. Yaws is endemic in 13 countries, with about 46,000 confirmed cases reported globally in 2022 (WHO). Papua New Guinea, the Solomon Islands, and several West and Central African countries carry most of the burden. WHO has set 2030 as the eradication target.

How is yaws spread?

Yaws spreads by direct skin-to-skin contact, usually through minor cuts, scratches, or insect bites. It is not sexually transmitted, not congenital, and not spread by food, water, or insect vectors. Most transmission happens between children playing or sharing bedding in close contact.

Can adults get yaws?

Yes, but it is uncommon. About 75-80% of new cases occur in children under 15. Adults in endemic areas are usually partially protected by childhood immunity. Travelers can occasionally acquire it after prolonged stays in rural endemic areas.

What does the first lesion of yaws look like?

The first lesion (the 'mother yaw') is a single, painless, raspberry-like papilloma, typically 1-5 cm wide, on the leg, foot, or buttock. It appears 9-90 days after exposure, does not hurt unless secondarily infected, and heals slowly over months even without treatment.

Is yaws painful?

The primary papilloma is usually painless. Pain becomes more prominent in secondary disease — painful sole thickening (plantar hyperkeratosis) and bone pain in the tibia and forearms. The difficulty walking on flat feet gave rise to the name 'crab yaws'.

What is the difference between yaws and syphilis?

Both are caused by closely related subspecies of Treponema pallidum and serology cannot distinguish them. Syphilis is sexually transmitted, can be congenital, and is global. Yaws is non-venereal, affects children, and occurs only in tropical regions.

How is yaws diagnosed?

Diagnosis is clinical plus serologic. A characteristic papilloma in a child in an endemic area plus a positive rapid treponemal test (DPP) makes the diagnosis. Quantitative RPR or VDRL confirms active disease and monitors treatment. PCR on lesion swabs is the gold standard.

How is yaws treated?

A single oral dose of azithromycin at 30 mg/kg (maximum 2 g) cures over 95% of cases. This replaced intramuscular benzathine penicillin as first-line in 2012 because pills are easier to give at community scale. Penicillin remains the alternative for pregnancy or resistance.

How quickly does treatment work?

Patients are no longer infectious within 24 hours of azithromycin or benzathine penicillin. Primary lesions begin to flatten within 1-2 weeks and heal over 4-8 weeks. Bone pain settles within 2-4 weeks. Antibody titers (RPR) take 3-6 months to fall fourfold, which is the laboratory marker of cure.

Can yaws come back after treatment?

Relapse is rare with adequate treatment but does occur in 1-3% of cases, usually within 6 months. Re-treatment with a second dose of azithromycin, or switching to benzathine penicillin, cures most relapses. Persistent failure should prompt PCR testing for the 23S rRNA macrolide-resistance mutation.

Is there a vaccine for yaws?

No vaccine for yaws is currently available. Eradication relies on mass drug administration with azithromycin, contact tracing, and improved community hygiene. A vaccine has been technically feasible but not prioritized because oral antibiotic therapy is already highly effective.

Where does yaws still occur?

WHO lists 13 endemic countries: Cameroon, Central African Republic, Congo, DRC, Côte d'Ivoire, Ghana, Indonesia, Liberia, Papua New Guinea, Solomon Islands, Timor-Leste, Togo, and Vanuatu. Papua New Guinea and Solomon Islands together account for over 70% of reported cases.

Why is yaws being eradicated, not just controlled?

Yaws affects only humans, has no animal reservoir, has a sensitive single-dose oral treatment, and is geographically confined. These features make it biologically eradicable — similar to smallpox. WHO set 2030 as the eradication target.

What is gangosa?

Gangosa is the destructive late-stage facial lesion of untreated tertiary yaws, eroding the nose, palate, and pharynx. It develops 5-10 years after primary infection. Modern surveillance has essentially eliminated new gangosa; most living cases reflect pre-1970s untreated childhood infections.

Can yaws spread through sexual contact?

No. Yaws is not a sexually transmitted infection. Sexual transmission has not been demonstrated for T. pertenue. Adolescent cases with positive treponemal serology require careful history-taking to distinguish yaws from acquired syphilis.

Is yaws fatal?

Yaws itself is rarely fatal. The historical burden has been disfigurement, school absence, and stigma rather than mortality. Death from yaws occurs only in extreme tertiary cases with secondary bacterial sepsis or in severely malnourished children with overwhelming co-infection.

What does azithromycin resistance in yaws mean?

A 2018 outbreak in Papua New Guinea identified yaws strains with the A2058G mutation in 23S rRNA, conferring high-level azithromycin resistance. Benzathine penicillin remains universally effective, and resistance has not spread widely outside the original outbreak focus.

Should travelers worry about yaws?

Risk to short-term travelers is very low. Yaws requires repeated close skin contact in rural endemic communities, typically over weeks to months. Any persistent unhealed skin papilloma after travel should be assessed by a tropical medicine clinician. No vaccine exists.

How is mass drug administration for yaws organized?

WHO's Morges Strategy involves total community treatment — every resident receives a single oral dose of azithromycin on a designated day, with coverage above 90% as the target. Re-surveys every 6-12 months identify new cases for repeat treatment until 3 consecutive years without new cases.

Can yaws be prevented without antibiotics?

Partial prevention is possible through improved hygiene — handwashing, soap, footwear, prompt cleaning of cuts — which reduces incidence by 30-50%. However, hygiene alone has not eliminated yaws anywhere.

Yaws.

What it is

How you might notice it

How it’s diagnosed

Treatment & cost

Causes & risk factors

Living with it

When to seek help

Related conditions

Easily confused with

Often appears alongside

Types and stages

Living with Yaws

Patient support resources

Frequently asked

Sources & references

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