Letter: Potential danger of hydatid disease of horse-dog origin

Echinococcus, Giardia and Cryptosporidium: observational studies challenging accepted dogma

The development of in vitro culture systems that allow the maintenance, and support the development of Echinococcus, Giardia and Cryptosporidium in the laboratory have had a significant impact on their biology and taxonomy and the epidemiology of infections they cause. This short retrospective review demonstrates how radical shifts in our understanding have occurred as a result of being able to grow these organisms in culture, and how molecular tools have helped in the interpretation of such research that often reflects the observations of earlier workers.

Strain differences in Echinococcus granulosus, with special reference to the status of equine hydatidosis in the United Kingdom

The genetics of speciation in the genus Echinococcus are briefly discussed. As the organism is a hermaphrodite and multiplies asexually in the larval stage, the genetic mechanism for the ready production of new strains is inherent in the life-cycle. Some biological, biochemical and nutritional differences between the horse and sheep strains are examined. The sheep strain may be grown to sexual maturity, in vitro, in a diphasic system; the horse strain fails to grow in such a system. Differences have also been demonstrated between the soluble proteins of the two strains. The sheep strain is infective to man but, probably, non-infective to horses. The horse strain (which is now the major strain in the U.K and Ireland) appears to be poorly infective to sheep and may prove to be non-infective to man. The importance of determining the basic characteristics of other strains of E. granulosus are also stressed.

Hydatidosis: a global problem of increasing importance

This review of recent literature reporting the occurrence of hydatid disease due to Echinococcus granulosus and E. multilocularis throughout the world emphasizes the global nature of the problem and the threat of its spread into those countries currently free from it. Attention is drawn to the urgent need for measures to prevent the importation of infected livestock and this would require the development of techniques for pre-mortem diagnosis and differentiation of hydatidosis and cysticercosis of animals. There must also be increased awareness of the possible occurrence of biological strains of the parasite which may be of greater or lower infectivity for man. In the absence of information on infectivity, studies concerning the prevalence of the disease may be meaningless.

Attempted infection of the rhesus monkey (Macaca mulatta) with the British horse strain of Echinococcus granulosus

Attention has been drawn to the fact that the occurrence of the cystic stage of Echinococcus granulosus in 60% of slaughtered horses represents a potential public health hazard (Thompson and Smyth, 1974). Williams and Sweatman (1963) regard this organism as a separate sub-species, E. granulosus equinus distinct from E. granulosus granulosus, but we prefer at this stage to refer to it as the horse “strain” which exhibits some small morphological differences from organisms of sheep origin.