History.—Some authorities think that a disease described by the Arabian physicians of the 10th century was yaws, but the first description of what was undoubtedly yaws was that of Oviedo, who in the 16th century described such an affection as existing in the West Indies. Bontius, later on, noted the existence of the disease in the East Indies as well as in the West Indies.
It is known that yaws often occurred in epidemic form on board the slave ships and it is thought that this disease may have been an African importation into the new world.
Geographical Distribution.—Yaws is essentially a disease of tropical regions.
In Africa it is very prevalent in the equatorial region, especially in the Congo Free State. It is also found more rarely in Tripoli and Algiers and to a less extent in the Sudan region. It is common in the West Indies and tropical America.
In Asia it is very prevalent in the Malay Peninsula, Siam, the East Indian Islands and in the Philippines. It does not exist in Japan. In many of the islands of the Pacific it is exceedingly prevalent, particularly in Samoa. It is also present in Northern Australia.
Etiology and Epidemiology
Etiology.—In view of the fact that many great authorities, especially J. Hutchinson, insisted upon the syphilitic nature of yaws it was a matter of great interest when Castellani, in 1905, discovered the causative organism which is characterized by the same sharp-cut, corkscrew spirals that are noted with the syphilitic spirochaete discovered by Schaudinn in the same year. Treponema pertenue is found in the epidermis of the yaws granuloma and has been demonstrated in lymphatic glands and spleen. Although it has not been demonstrated in the blood, through microscopical examination, it must exist there as monkeys infected with the blood of yaws patients develop the lesions of yaws in which the spirochaetes are present. Another name for the organism is Spirochaeta pallidula; this however is only a synonym.
Inoculation experiments as well as clinical manifestations show yaws and syphilis to be distinct. Thus Charlouis, in 1881, inoculated a native suffering from typical yaws wistations of syphilis followed. There have been many instances of the development of yaws, naturally and by inoculation, in those affected with syphilis. Nichols has shown that a rabbit which had been infected intratesticularly with T. pallidum and then cured by salvarsan did not show immunity to T. pertenue when the latter was used to infect the testicle.
In the monkey inoculation over the eyebrow gives a flat dry and scaly lesion with syphilitic material while yaws inoculation gives a softer, more oedematous one.
Levaditi and Nattan Larrier have noted that monkeys which had been inoculated with syphilis were immune to yaws inoculation but yaws monkeys could be infected with syphilis, thus indicating that yaws was a mild form of syphilis. In Guam, it has recently been shown that 68% of cases of gangosa, a disease supposed to be a tertiary form of yaws, give a positive luetin reaction. This would indicate a close relationship between yaws and syphilis.