Yaws is a chronic, non-venereal infectious disease primarily affecting the skin, bones, and joints. Historically, it has impacted communities in warm, humid, and tropical regions across Africa, Asia, Latin America, and the Pacific islands. It is part of a group of bacterial infections known as endemic treponematoses, which also include bejel and pinta. Global health initiatives are working towards its worldwide elimination.
How Yaws Spreads
Yaws is caused by the bacterium Treponema pallidum subspecies pertenue, closely related to the one that causes syphilis. Unlike syphilis, yaws spreads through direct skin-to-skin contact with infectious lesions, not sexually. The bacteria typically enter the body through minor cuts, scratches, or insect bites.
Transmission commonly occurs among children, who often come into direct contact during play in crowded or unhygienic environments. Early-stage infectious lesions contain a high concentration of bacteria, allowing easy spread. Poor socioeconomic conditions and limited healthcare access also contribute to yaws’ persistence.
Recognizing the Stages of Yaws
Yaws progresses through distinct stages: primary, secondary, and tertiary, which can sometimes overlap. The initial sign, the “mother yaw,” usually appears at the infection site within 9 to 90 days. This lesion begins as a painless, reddish bump that can grow into a raised, wart-like growth (papilloma) or an ulcer, sometimes covered with a yellow crust. Primary lesions are most frequently found on the legs and ankles and typically heal within three to six months, often leaving a light-colored scar.
The secondary stage emerges weeks to months after the primary lesion, characterized by widespread skin lesions across the body, including the face, arms, and legs. These can manifest as multiple raised papules, plaques, or thick, fissured skin on the palms and soles, sometimes called “crab yaws” due to altered gait. Individuals may also experience swollen lymph nodes, bone pain, and fever.
The tertiary stage can develop years after initial infection, affecting a smaller percentage of untreated individuals. This stage involves destructive lesions of the skin, bones, and cartilage, leading to severe disfigurement and disability. Examples include gummas (soft, rubbery tumors), gangosa (destruction of the nose and palate), and gondou (bone spurs in the upper jaw). These complications are now rare due to treatment efforts.
Identifying and Treating Yaws
Diagnosing yaws often relies on clinical examination of characteristic skin lesions, especially in endemic regions. However, since Treponema pallidum subspecies pertenue is difficult to distinguish from syphilis-causing bacteria, serological tests are commonly used for confirmation and surveillance. Non-treponemal tests, such as the Rapid Plasma Reagin (RPR) test, indicate active infection, with levels decreasing after successful treatment.
Specific anti-treponemal antibody tests, like the Treponema pallidum particle agglutination (TPPA) assay, detect antibodies that remain positive for life, indicating past or present infection. Dual rapid tests are now available, simplifying field diagnosis by simultaneously detecting active and past infections. For definitive confirmation and to monitor antibiotic resistance, polymerase chain reaction (PCR) can detect the bacteria directly from skin lesions.
Yaws is highly treatable with antibiotic regimens. A single oral dose of azithromycin (30 mg/kg, max 2 grams) is the preferred treatment due to its ease of administration in large-scale campaigns. Historically, a single intramuscular injection of benzathine penicillin G (1.2 million units for adults, 600,000 for children) was standard. Both treatments lead to rapid healing of early lesions, often within two to four weeks, with bone pain improving within days. Treating close contacts also helps prevent further spread.
Global Efforts to Eliminate Yaws
Global efforts to eliminate yaws have a long history, with significant success in the 1950s and 1960s through mass penicillin treatment campaigns, reducing cases by an estimated 95% worldwide. Despite this, the disease re-emerged in some areas, prompting renewed initiatives. The World Health Organization (WHO) launched a new eradication strategy.
The current strategy focuses on mass drug administration (MDA) with oral azithromycin in endemic communities. This involves administering a single antibiotic dose to an entire population to interrupt transmission. Challenges include consistent surveillance in remote areas, addressing re-emergence, and monitoring for antibiotic resistance. Despite obstacles, effective oral treatment and lessons from past campaigns continue to drive progress towards yaws elimination.