Application of ultrasound in diagnosis, treatment, epidemiology, public health and control of Echinococcus granulosus and E. multilocularis
The last 30 years have seen an impressive use of ultrasonography (US) in many fields of veterinary and clinical medicine and the technique is being increasingly applied to a wide variety of parasitic infections including the cestode zoonoses Echinococcus granulosus and E. multilocularis. US provides real-time results which are permanently recordable with a high resolution and diagnostic accuracy. These properties, coupled with the clinical value of the images obtained and the non-invasive nature of the test which is safe, require no special patient preparation time; it is easy to operate and this has resulted in the establishment of US as the diagnostic technique of choice for cystic (CE) and alveolar (AE) echinococcosis. The lack of ionizing radiation and side-effects mean that examination times are not restricted. The hand-held probes facilitate what amounts to a rapid, bloodless non-invasive laparotomy, enabling a search from an infinite number of angles for lesions producing information on their number, size and type of cysts, their location and clinical implications. Such clinical information has facilitated the development of treatment protocols for different cyst types. Less invasive surgical techniques, such as US guidance for PAIR (Puncture, Aspiration, Injection, Re-aspiration), PAIRD (PAIR plus Drainage) or PPDC (Percutaneous Puncture with Drainage and Curettage) are also possible. Longitudinal US studies have facilitated monitoring the effects of the outcome of treatment and chemotherapy. Portable ultrasound scanners which today weigh as little as a few pounds, powered by battery or generators have facilitated the use of the technique in mass community-based screening studies. The majority of these studies have been conducted in remote, low socio-economic areas where there were few, if any, hospitals, veterinary facilities, schools or trained personnel. The surveys led to the discovery of unexpectedly high prevalences of CE and AE in asymptomatic individuals of endemic areas and especially amongst transhumant or nomadic pastoralists living in various parts of the world. Screening for CE and AE is justified as an early diagnosis leads to a better prognosis following treatment. The application of US in field and clinical settings has led to a better understanding of the natural history of CE and AE and to the development of a WHO standardized classification of cyst types for CE. This classification can be used in helping define the treatment options for the different cysts found during the surveys, which in turn can also be used to calculate the public health cost of treating the disease in an endemic community. The case mix revealed can also influence the specificity (particularly proportions of cyst types CE4 and CE5 and cystic lesions – CL) of US as a diagnostic test in a particular setting. Community based US surveys have provided new insights into the public health importance of CE and AE in different endemic settings. By screening whole populations they disclose the true extent of the disease and reveal particular age and sex risk factors. Through the treatment and follow-up of all infected cases found during the mass screening surveys a drastic reduction in the public health impact of the disease in endemic communities can be achieved. Educational impacts of such surveys at the national, community and individual levels for both professional and lay people are beginning to be appreciated. The translation of the information gained into active control programmes remains to be realized. In areas where intermediate hosts, such as sheep and goats, are not slaughtered in large numbers mass US screening surveys to determine the prevalence of CE in livestock has proved possible. Longitudinal studies in such intermediate hosts would reveal changes in prevalence over time, which has been used as a marker for control success in other programmes. Mass US screening surveys in an ongoing control programme in Argentina has demonstrated the early impact of control in the human population and identified breakthroughs in that control programme. Mass US screening surveys must adhere to the highest ethical standards and the outcome of surveys should result in the application of appropriate WHO recommended treatment options for different cyst types. Follow-up strategies have to be in place prior to the implementation of such surveys for all infected individuals who do not require treatment and for all suspected, but not confirmed, cases found during the surveys. The use of US in community screening surveys has revealed the complexity of ethical issues (informed consent, confidentiality, follow-up, detection of lesions that are not the focus of the study etc) and also provided real solutions to providing the most ethical guidelines for the early detection and treatment of CE and AE.
Key Words: Ultrasound; epidemiology; public health; community based mass screening; cystic and alveolar hydatid disease.