Yaws: Symptoms, Types, Causes and Treatment

Yaws is a fascinating yet neglected tropical disease that primarily affects children in remote, impoverished communities of the world's warmest regions. Known for its ability to cause chronic skin and bone lesions, yaws has been a target of global eradication campaigns for decades—yet it stubbornly persists in several countries. Understanding its symptoms, various types, underlying causes, and the latest advancements in treatment is key both for healthcare professionals working in endemic regions and for anyone interested in the ongoing efforts to eliminate this ancient disease.

Symptoms of Yaws

Yaws manifests itself mainly as skin and bone lesions, but the disease's course and presentation can be surprisingly varied. Early identification of symptoms is crucial for timely treatment and for breaking the chain of transmission, especially in communities where healthcare access is limited.

Phase	Main Features	Age Group	Source(s)
Primary	Painless papule or ulcer, often moist	Children	3 5 7
Secondary	Multiple skin lesions, papillomas, bone pain, swollen joints	Children/Teens	5 7
Tertiary	Destructive bone/soft tissue lesions, disfigurement	Adolescents/Adults	6 7
Latent	No visible symptoms, positive serology	All ages	5 7

Table 1: Key Symptoms

The Stages of Yaws: How Symptoms Evolve

Yaws unfolds in three clinical stages, each with its own hallmark symptoms.

Primary Yaws

• Begins as a single, painless papule at the site of infection, often on the legs or arms.
• The papule develops into a moist, "raspberry-like" (frambesiform) ulcer that may be mistaken for other tropical ulcers.
• Lesions are highly contagious during this phase 3 5 7.

Secondary Yaws

• Weeks to months after the primary lesion, secondary yaws sets in.
• Characterized by multiple skin lesions that may appear as papillomas (cauliflower-like growths), scaly patches, or warty nodules.
• Bone pain, swelling of joints, and periostitis (inflammation of the bone surface) are common.
• Lesions can affect the soles of the feet, causing difficulty walking (crab yaws) 5 7.

Tertiary Yaws (Late Stage)

• If untreated, yaws can progress over years into the destructive tertiary phase.
• Chronic inflammation leads to severe, disfiguring destruction of the skin, cartilage (including the nose), and bones.
• This can result in disabling deformities and social stigma 6 7.

Latent Yaws

• Some individuals may not display visible symptoms but test positive for yaws with serological (blood) tests.
• These latent cases are important in sustaining transmission within communities 5 7.

Distinguishing Yaws from Other Ulcerative Diseases

Because yaws lesions can resemble those caused by other skin pathogens—such as Haemophilus ducreyi—accurate diagnosis is essential. Features more suggestive of yaws include:

• Circular ulcer shape
• Central granulating tissue
• Indurated (hard) edges

Haemophilus ducreyi ulcers tend to be smaller, less circular, and lack indurated edges 3.

Types of Yaws

While "yaws" is often spoken of as a single disease, it actually encompasses several clinical forms and stages, each with distinct features and epidemiological significance.

Type/Stage	Description	Transmission Mode	Source(s)
Primary Yaws	Initial lesion at infection site	Skin contact	5 7
Secondary Yaws	Multiple lesions; bone/joint involvement	Skin contact	5 7
Latent Yaws	Asymptomatic; positive serology	Potentially infectious	5 7
Tertiary Yaws	Destructive, late complications	Not contagious	6 7
Atypical Yaws	Variants or coinfections (e.g. with H. ducreyi)	Skin contact	3 4

Table 2: Types and Stages of Yaws

Clinical Types and Their Significance

Primary, Secondary, and Tertiary Yaws

• Primary: The entry point, featuring the initial, highly infectious lesion.
• Secondary: The most contagious phase, with widespread skin and occasional bone involvement.
• Tertiary: Not infectious, but responsible for the worst long-term outcomes due to chronic tissue and bone destruction 5 6 7.

Latent Yaws

• Individuals harbor the bacterium without symptoms.
• Latent infections maintain the reservoir of disease in communities and may relapse into active disease 5 7.

Atypical Forms and Coinfections

• In some endemic regions, chronic skin ulcers initially thought to be yaws may result from other pathogens, especially Haemophilus ducreyi.
• Coinfections can complicate clinical diagnosis and require molecular tools (like PCR) for accurate identification 3 4.
• In certain mass drug administration (MDA) settings, some skin ulcers remained unexplained even after testing for both yaws and H. ducreyi 4.

Molecular Types and Strain Diversity

• Modern molecular methods, such as multilocus sequence typing (MLST) and PCR-based subtyping, have identified a wide variety of yaws strains circulating in different regions 1 2.
• Understanding strain diversity helps track transmission and potential outbreaks, and supports eradication campaigns 1 2.

Causes of Yaws

The story of yaws begins with a unique bacterium—but epidemiology and social factors play equally essential roles in its persistence.

Cause	Details	Key Region(s)	Source(s)
Treponema pertenue	Spiral-shaped bacterium (spirochete)	Tropics, especially Africa, Asia, Pacific	5 6 7
Transmission	Skin-to-skin contact with infectious lesions	Children in rural, humid areas	5 6 7
Risk Factors	Poverty, poor hygiene, crowded living	Remote villages	5 6
Other Pathogens	Haemophilus ducreyi (mimics yaws ulcers)	Papua New Guinea, Ghana	3 4

Table 3: Causes and Risk Factors

The Bacterium: Treponema pallidum subsp. pertenue

• The key culprit is Treponema pallidum subspecies pertenue—a close relative of the syphilis bacterium (T. pallidum subsp. pallidum) 6 7.
• It is a spiral-shaped bacterium (spirochete), adapted to survive in humid, tropical environments 6.
• Unlike syphilis, yaws is not sexually transmitted and does not pass from mother to fetus 7.

Transmission: How Yaws Spreads

• The disease spreads through direct, nonsexual skin-to-skin contact, especially when children play together.
• Moist lesions are teeming with bacteria and highly infectious.
• Crowded living conditions, poor hygiene, and lack of access to clean water facilitate transmission 5 6 7.

Environmental and Social Determinants

• Yaws remains a disease of poverty, thriving in remote, underserved communities where health infrastructure is weak.
• Underreporting is common, as many cases go unrecognized or are misdiagnosed 6.
• False sense of security after previous eradication campaigns has led to resurgence in some countries 6.

The Role of Other Pathogens

• Recent studies have shown that ulcers resembling yaws can also be caused by Haemophilus ducreyi, complicating clinical diagnosis 3 4.
• Accurate laboratory diagnosis (including PCR) is essential for correct treatment and control 3 4.

Treatment of Yaws

Thanks to medical advances and global health initiatives, yaws is now among the few infectious diseases considered eradicable. The cornerstone of this effort is safe, effective, and scalable treatment.

Treatment	Dosage/Method	Effectiveness	Source(s)
Benzathine Penicillin	Single intramuscular injection	>90% cure rate	7 8 12
Azithromycin	Single oral dose (30 mg/kg)	Non-inferior to penicillin; suitable for mass treatment	7 8 9
Mass Drug Administration (MDA)	Community-wide azithromycin	Rapid reduction in cases; risk of missed cases/recrudescence	9 10 11
Resistance Concerns	Macrolide resistance emerging	Isolated cases reported	10

Table 4: Yaws Treatment Approaches

The Gold Standard: Penicillin

• For decades, a single intramuscular injection of long-acting benzathine penicillin has been the definitive cure for yaws.
• Over 90% of cases are cured, with failures often linked to low initial infection levels or high-background infection rates 7 8 12.

The Game Changer: Oral Azithromycin

• Recent clinical trials have shown that a single oral dose of azithromycin (30 mg/kg) is just as effective as penicillin for treating yaws 7 8.
• Oral administration is easier, safer (no needles needed), and allows treatment of entire communities in one campaign—a critical advantage for eradication efforts 8 9.
• Mild side effects (nausea, diarrhea) can occur, but are generally well tolerated 9.

Mass Drug Administration (MDA)

• The WHO strategy for yaws eradication centers on mass azithromycin administration to all residents of endemic communities, followed by targeted treatment of any new cases 9 11.
• MDA campaigns have demonstrated rapid and dramatic reductions in both active and latent yaws cases 9 11.
• Integration with programs for other diseases (like trachoma) is possible, provided dosages are appropriate 11.

Challenges: Recrudescence and Resistance

• Despite initial success, yaws can re-emerge if even a small proportion of the population is missed during MDA; repeat campaigns may be necessary 10.
• Isolated cases of azithromycin-resistant yaws have been documented, underlining the need for ongoing surveillance and resistance monitoring 10.
• Some chronic ulcers may be due to other bacteria (e.g., H. ducreyi) and will not respond to yaws treatment 3 4.

Predictors of Treatment Failure

• Factors such as low initial antibody titers and residence in high-prevalence villages are linked to higher rates of treatment failure 12.
• Strengthening surveillance and integrating diagnostic testing help ensure treatment success and prevent recurrence 4 10.

Conclusion

Yaws remains a significant public health challenge in certain tropical regions, particularly among children living in poverty. However, the global health community has made remarkable strides in understanding, diagnosing, and treating this disease.

Key takeaways:

• Symptoms: Yaws progresses through primary, secondary, and tertiary stages, each with distinct skin and bone manifestations. Latent infections sustain disease transmission 5 6 7.
• Types: The disease includes classical stages and atypical forms; coinfections with other pathogens can complicate diagnosis 3 4 5 6 7.
• Causes: Treponema pallidum subsp. pertenue is the causative bacterium, transmitted through skin contact in humid tropical environments. Social determinants play a major role 5 6 7.
• Treatment: A single dose of oral azithromycin is as effective as penicillin and facilitates mass treatment, but surveillance for resistance and missed cases is vital 7 8 9 10 11 12.
• Eradication Prospects: With integrated diagnosis, robust surveillance, and community engagement, yaws could become one of humanity’s next eradication success stories.

Yaws teaches us the power of simple, community-driven interventions—and the importance of not letting our guard down, even against diseases we believe to be nearly conquered.