CLINICAL RESEARCH

Yaws: An endemic infectious disease

Dr A.C. Dhariwal, National Institute of Communicable Diseases, Delhi, India (e-mail: dr_dhariwal@yahoo.co.in) Dr D.C.Jain, Dr Shiv Lal, National Institute of Communicable Diseases, New Delhi, India Professor Andre Meheus, Department of Epidemiology and Social Medicine, University of Antwerp, Antwerp, Belgium Dr Jean-Jannin, Dr Lorenzo Savioli, Dr Kingsley Asiedu, Department of Control of Neglected Tropical Diseases, World Health Organization, Geneva, Switzerland

Yaws, pinta, and endemic syphilis (bejel), grouped as nonvenereal endemic treponematoses are chronic bacterial infections caused by treponemes. These are mostly prevalent amongst the communities living in poor, unhygienic conditions in hot and humid areas. Although seldom fatal, the treponematoses cause public health, social and economic problems. In the landmass between the Tropics of Cancer and Capricorn, these infections constituted a public health problem.

An early case of yaws (courtesy: professor Henri Asse, Cote d’ Ivoire)

Nonvenereal treponematoses are distinguished from venereal syphilis on the basis of clinico-epidemiological features as the treponemes that cause these diseases have identical morphology. With the availability of penicillin for the treatment of nonvenereal treponematoses, the fight against endemic treponematoses has been a priority for the World Health Organization (WHO) since its creation in 1948. In the period 1952-1964 WHO, in close collaboration with UNICEF, launched the Global Endemic Treponematoses Control Programme (TCP), which became a real unusually successful public health campaign. Over 160 million people were examined and approximately 50 million patients, contacts, and latent cases were treated in 46 countries (Figure 1), reducing the overall prevalence of these diseases by more than 95%. The prevalence of active yaws lesions was reduced from over 20% to less than 1% in many rural areas. By the 1990s only a few countries still had yaws (Figure 2).

The control strategy subsequently changed from a vertical programme to be integrated into the basic health services. These basic health services were to cope with the remaining, “last cases” of endemic treponematoses in the community until eradication had been achieved. Because of relaxation of active surveillance activities after the mass campaigns, the goal of eradication was not attained and a number of foci of transmission remained. By the end of the 1970s, a resurgence of the endemic treponematoses had occurred in many areas of the world.

The necessity for renewed efforts was recognised by the World Health Assembly and expressed in WHA Resolution 31.58. Since 1984, a global conference in Washington DC, three major regional meetings and partners’ meetings have brought the problem of endemic treponematoses to the attention of health policy makers and the international donor community. This resulted in renewed control efforts in a number of countries. The South-east Asia Region of WHO has set the target of Yaws Eradication by 2012 and efforts are going on in this direction. In view of the persistence and resurgence of yaws, a new global initiative to eliminate yaws was launched at a meeting organised by the WHO Department of Control of Neglected Tropical Diseases (NTD) at its Headquarters at Geneva in January 2007.

Causative agent

Treponema pallidum, the causative organism of syphilis was discovered in 1905 by Fritz Schaudinn and in the same year Castellani discovered its subspecies pertenue, the causative organism of yaws. The etiological agents of endemic syphilis and yaws are generally held to be identical with T. pallidum and have been designated as T. pallidum ssp. endemicum and ssp. pertenue, respectively. Infection with one treponema provides partial protection against another, which indicates that they share common antigens. There is no laboratory test that can distinguish these treponemes from one another.

Because of small size and mass of treponemes, they cannot be seen with an ordinary microscope unless a dark-field condenser is used. Their characteristics are:

They look like thin, silver threads coiled like a corkscrew about 3 to18 μm long having 8 to 20 corkscrew spirals. They stain very poorly because their thickness approaches the resolution of the light microscope.
They are motile with a characteristic rapid spinning motion.
The organisms are delicate requiring ph between 7.2–7.4, temperatures in the range 300 C to 370 C and a micro-aerophilic environment.
The structure of these organisms is somewhat different: the cells have a coating of glycosamino-glycans, which may be host-derived, and the outer membrane covers the three flagella that provide motility.

In addition, the cells have a high lipid content (cardiolipin, cholesterol), which is unusual for most bacteria. Cardiolipin elicits “Wassermann” antibodies that are diagnostic for syphilis.

Treponema possesses a complex antigenic makeup that is difficult to determine because the organisms cannot be grown in vitro. Man is their natural host. Treponemal antibodies are demonstrable in some proportion of nonhuman primates in regions of Africa where human yaws and endemic syphilis are common, and pathogenic treponemes have been found in skin lesions and lymph nodes of seropositive animals. These treponemes have produced yaws-like lesions in susceptible monkeys and hamsters.

Epidemiology

Epidemiological characteristics of yaws is summarised in Table 1.

Modes of transmission

Yaws is a disease of young children. Scanty clothing, poor hygiene, and frequent skin trauma favour transmission of yaws among children. Spread occurs by direct contact with infected lesions and perhaps by passive transfers of treponemes by insects. Role of transmission through fomites is insignificant.

Present status

There is no more regular system of reporting of yaws in many countries today. In Africa, recent reports indicate that the disease is still present in Ivory Coast, Cameroon, Congo, Ghana, Togo, and Benin. In the Americas, foci of yaws were known in Haiti, Dominican Republic, St. Lucia, and St. Vincent, Peru, Colombia and Ecuador, a few areas of Brazil; and Guyana and Suriname but the current status in these countries remains unknown.

In South East Asia, active yaws cases have been reported from only two countries during 2006 – Indonesia and Timor Leste. India declared achievement of Yaws Elimination in 2006 defined as no reporting of new early cases supported by laboratory investigations and on the basis of good quality search in all endemic areas of the country, and validated by independent appraisal. Figure 3 shows the elimination of the disease in India.

In the Western Pacific region, active foci still exist in Papua New Guinea.

Biologic relationships

Specific humoral antibodies to T. pallidum are produced in individuals with yaws, pinta, or endemic syphilis, but the time of appearance of antibodies after onset of infections is variable. The fluorescent trepone- mal antibody absorption (FTA-ABS) test, the T. pallidum hemagglutination test (TPHA), and the T. pallidum immobilisation (TPI) test cannot differentiate among the treponematoses.

Individuals who have had yaws or pinta are considered relatively immune to syphilis, and persons with active pinta or syphilis cannot be superinfected with T. pallidum ssp. pertenue by experimental inoculation.

Clinical manifestations

In areas where yaws has long been endemic, there are synonyms for it in the local language. Of about 80, some of its synonyms are: Pian (French), Framboesia (Dutch/German), Buba (Spanish), Bouba (Portuguese), Parangi (Sri Lanka), Coco (Fiji island) and Dube (Gold Coast). The term “Yaws” is thought to be of Caribbean origin. In the language of the Caribs India people, “Yaya” was a word for “sore”.

The incubation period is three to four weeks. Yaws produces a great variety of skin, bone and joint lesions that have been categorised as early and late yaws lesions. Early lesions are usually infectious and occur in the first five years of illness and heal slowly leaving scar, hyperpigmentation, or depigmentation while late lesions are not infectious and occur in about 10% of cases, starting five years or more after infection. A thin yellow crust of serous exudates teeming with T. pertenue covers the initial early lesions.

Early lesions are often pruritic, and scratching facilitates both spread of the infection to other areas of the body by autoinoculation and the transmission of the disease within the community.

The early lesions tend to occur in crops, which often overlap with one another.
Mixed (polymorphous) forms of lesions are often present in the same patient.
A change in climate may influence the number and morphology of yaws lesions. In the dry season fewer lesions are present and they tend to be of the macular type; papillomata tend to retreat to the more humid areas of the body surface such as axilla and anal folds.
Erythema and induration do not occur in early yaws lesions. Painful papilloma on the soles of the feet result in a crab-like gait referred to as “crab yaws”.
Histologic findings in early lesions are mononuclear-cell infiltration, acanthosis, hyperkeratosis, and the presence of many treponemes while late lesions show endarteritis.

Constitutional symptoms such as fever and malaise are not significant in yaws. The lymph nodes draining cutaneous lesions are frequently enlarged and tender, but they do not suppurate. Nocturnal bone pain and tenderness of the tibial shaft and other long bones due to periostitis are common in early yaws.

Despite the variety of yaws lesion, in endemic areas the disease can usually be accurately diagnosed on the basis of clinical findings alone. It becomes less reliable in the areas where prevalence has decreased, neces- sitating the use of easily performed serologic tests, such as rapid plasma reagin (RPR) card test. T. pertenue can be demonstrated by dark-field examination in early cutaneous lesions but should not be confused with other spirochetes found in tropical ulcers. TPHA and FTA-ABS tests are more specific.

Treatment

Treatment is similar for all the endemic treponematoses. Single intramuscular injection of 1.2 million units of benzathine penicillin in adult and half this dose in children under 10 years results in rapid resolution of lesions and prevents recurrence. In persons who are allergic to penicillin, oral tetracycline hydrochloride in adults and erythromycin in children (<8 years), pregnant and lactating mothers is recommended for a period of 15 days in four divided doses.

Prevention and control

The following measures are applied to prevent the nonvenereal treponematoses:

General health promotion measures: health education of the public about the value of better sanitation, including liberal use of soap and water and the importance of improving social and economic conditions over a period of years to reduce the incidence. Improve access to health services.
Organise intensive control activities on a community level suitable to the local problem; examine entire population, and treat patients with active or latent disease. Treatment of asymptomatic contacts is beneficial, and WHO recommends treating the entire population when the prevalence rate for active disease is above 10% (Total Mass Treatment); if prevalence is 5-10% , treat patients, contacts and all children below 15 (Juvenile Mass Treatment); if less than 5% , treat active cases plus household and other contacts (Selective Mass Treatment). Periodic clinical resurveys and continuous surveillance are essential for success.
Serological surveys for latent cases, particularly in children, to prevent relapses and development of infective lesions that maintain the disease in the community.
Provide facilities for early diagnosis and treatment as part of a plan in which selective epidemiological control campaigns are eventually consolidated into permanent local health services.
Treat disfiguring and incapacitating late manifestations.

Conclusion

Yaws is amenable to eradication because of the following factors:

Man is the only reservoir of infection;
The distribution of the disease is focalised, thus allowing targeted interventions;
The causative organism is sensitive to penicillin;
The available drug, Benzathine Penicillin, is safe, stable, inexpensive, and effective in a single administration.

Learning from the success of smallpox eradication, experts suggest that strategy for yaws eradication should emphasise ongoing active surveillance, investigation of outbreaks, and the treatment of active cases and their contacts rather than mass treatment.

Figures

Figure 1: Map of the world showing the distribution of yaws in the 1950s (Source: P.L. Perine, D.R. Hopkins, P.L.A. Niemel, R.K. St. John, G. Causse, G.M. Antal, Handbook of Endemic Treponematoses: Yaws, Endemic Syphilis and Pinta, World Health Organization, Geneva, 1984).

Figure 2: Map of the world showing the distribution of cases in the early 1990s (A. Meheus, G.M. Antal, The endemic treponematoses: not yet eradicated, World Health Stat. Q 45 (1992) 228–237). Figure 3: A graph showing the progressive elimination of yaws in India.

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