Ultrasound in the diagnosis of parasitic disease

Progress towards international adoption of the World Health Organization ultrasound classification of cystic echinococcosis

Cystic echinococcosis (CE) is a global parasitic zoonosis for which ultrasound (US) is the gold standard modality for diagnosis. In 2003, the WHO published a standardized US classification of CE, on which WHO treatment guidelines are based. In 2014, global adoption of the classification was questioned by a publication which indicated that, between 2004 and 2014, only half of studies utilizing a classification used the WHO classification. More recent studies have demonstrated that the WHO classification best reflects the natural history of CE, and is used with high reliability by experts in the field; despite these attributes, the classification's impact is ultimately limited by the extent of its adoption. A PubMed search using the terms "Echinococcus granulosus ultrasound," "Echinococcus granulosus classification," "cystic echinococcosis ultrasound," and "cystic echinococcosus classification" revealed publications on human CE utilizing a US classification. Classification(s) used, year of publication, and the country of the first author's institution were recorded. From 2004 to 2010, the WHO classification was used in 50% or fewer of included publications for 6 of the 7 years. After 2011, it appeared in a low of 75% (2013) to a high of 96% (2017) of included publications. Of all included studies published from 2004 to 2017, the WHO classification was referenced in 18% (3 of 17) from Africa, 64% (32 of 50) from Asia, 79% (89 of 113) from Europe, 89% (8 of 9) from North America, and 100% (9 of 9) from South America. Findings suggest that the WHO classification has been progressively taking preference to other classifications, with rate of adoption depending on continent of origin of the research. Residual use of the classification developed by Dr. Hassen Gharbi of Tunisia in 1982, used widely prior to development of the WHO classification (which reversed two stages in Gharbi's classification in order to more closely reflect the natural history of CE) suggests that adoption of a new classification takes time and varies regionally.

A portable ultrasound based screening study on the prevalence and risk factors of cystic echinococcosis in primary school children in East Turkey

The tapeworm Echinococcus granulosus constitutes a major public health concern, since its larval stage causes cystic echinococcosis (CE) which is a life-threatening zoonotic disease in many parts of the world. The purpose of the present study was to perform a screening study in order to investigate the prevalence and risk factors of CE using a portable ultrasound (US) in a representative sample of 2500 primary school children aged 7-14 in East Turkey, where CE is known to be endemic. The students were scanned by portable US while standing, with special attention to the liver, spleen, pancreas, and kidneys. The US scan was followed by a physical examination. In addition, a questionnaire was distributed to all students for completion with the assistance of their teachers regarding their demographic and social characteristics as well as their hygienic habits possibly related to CE. Students found positive were subjected to serologic examination. The US based prevalence was 0.2%. Organ involvement was 0.12% for liver and 0.08% for kidney. The response rate of the questionnaire survey was 93%. The risk factors found to be significant (P<0.05) for CE infection were hand washing and family relative with CE. The results of this study indicate that CE infection is an important public health problem in East Turkey requiring appropriate control measures.

Sonographic management of complicated cystic echinococcosis

INTRODUCTION

In this survey we evaluated the usefulness of ultrasonography (US) in the diagnosis, and in the treatment of complicated hydatid cysts.

MATERIALS AND METHODS

From June 1985 to June 2004, 221 patients with 294 hydatid cysts were examined. Twenty patients (9.0%) presented 22 complicated cysts (7.4%): 9 with infection, 5 ruptured into the bile ducts, 2 bilomas, 2 cysto-pleural fistulas, 2 allergic reactions, 1 rupture into the peritoneum and 1 intrasplenic hematoma. In all cases, US yielded a specific or suspected diagnosis, also in complications affecting non-hepatic sites, confirmed by computed tomography (CT), endoscopic papillotomy or percutaneous US-guided sampling. All patients with complicated cystic echinococcosis were treated with Albendazole 800 mg/day for at least 3 months. In addition to this therapy, 12 underwent US-guided drainage (9 infected cysts, 2 bilomas, 2 cysto-pleural fistulas, 1 intrasplenic hematoma); of these patients 3 subsequently underwent surgery because US-guided treatment was ineffective. Five patients were treated with perendoscopic sphincterotomy for obstruction of the bile passages, while 3 patients received only medical therapy.

RESULTS

Medical, echoguided and surgical treatments led to resolution of the complications and complete remission of the parasitic pathology in 19/20 patients (95%) and in 21/22 cysts (95.4%). There was partial remission in 1 case only. The therapy did not cause major complications and the results were confirmed during follow-up lasting from 5 months to 15 years (mean time 3 years).

DISCUSSION AND CONCLUSION

This study shows that the incidence of complications of hydatid cysts is low and that correct echographic management allows a rapid diagnosis and optimization of treatment in most cases.

Application of ultrasound in diagnosis, treatment, epidemiology, public health and control ofEchinococcus granulosusandE. 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 zoonosesEchinococcus granulosusandE. 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.

Classification, follow-up and recurrence of hepatic cystic echinococcosis using ultrasound images

Ultrasound image and morphological structure of hepatic cystic echinococcosis (CE) were analysed in 277 human cases (385 hepatic hydatid cysts). These included 65 CE cases from community surveys carried out between 1995 and 2000 in 3 countries (China, Mongolia and Jordan) and 212 cases from a clinical hospital survey from Xinjiang, China. A new simplified WHO ultrasound classification for human CE was assessed, and considered useful. It is proposed that type, size and number in particular need to be included in the ultrasound classification of hepatic CE. For comparative purposes 6 categories of type were classified in the study as Type 0 to Type 5 (T0-T5): T0, univesicular without pathognomonic signs; T1, univesicular with pathognomonic signs; T2, cysts with sagging or floating laminated membrane; T3, cysts containing daughter cysts; T4, solid mass or mixed cysts; and T5, cysts with partial or full calcifications. This differs from the WHO classification wherein Type T3 cysts (daughter cysts present) are considered a pathological stage to occur in general prior to the sagging or floating membrane (T2) stage. Recurrent hydatid cysts in the liver were also studied based on morphological structures observed directly from surgical intervention. Case follow-up over 1-5 years since endocystectomy in the community surveys indicated 10% (2/10) recurrence of cysts in the residual surgical cavity. Recurrent CE included 2 (2/4) cases after percutaneous treatment.

Performance characteristics and quality control of community based ultrasound surveys for cystic and alveolar echinococcosis

The probability of disease given the results of a test, is called the predictive value of the test. The predictive value of a test is not a property of the test itself but will vary according to the prevalence of the disease in the studied population. The positive predictive value (PPV) is the probability that the subject tested has the disease given that a positive result is obtained. The negative predictive value (NPV) is the probability that the subject tested is normal given that a negative result is obtained. As the prevalence of a disease in a population approaches zero so does the PPV and most of the positive cases will be 'false positives'. Conversely the NPV will be very high at low prevalences and there will be few 'false negative' results. The sensitivity and specificity of a test are properties of the test and do not vary with prevalence. The higher the sensitivity and specificity of a particular test the greater the predictive values will be at any given prevalence of the disease. Ultrasound (US) is increasingly used for detecting lesions due to cystic and alveolar echinococcosis (CE and AE) and portable US scanners facilitate community based mass screening surveys in remote rural communities. Screening is justified with AE and CE in endemic areas as diagnosis at an early stage can lead to a better prognosis following treatment. The sensitivity and specificity of US has been reported to be between 88-98% and 95-100% respectively for CE and the sensitivity is a little higher for AE. Both species have pathognomonic signs on US and the technique is considered to be the 'gold standard' although it is still an imperfect test. Clinical, laboratory and epidemiological data also play an important role in the diagnosis of CE and AE. US results where possible, should be evaluated in relation to these findings. Suspected CE and AE images, may benefit from the use of other imaging techniques such as magnetic resonance imaging, computerised tomography and in the case of AE angiography or cholangiography. Immunological tests or molecular biological techniques also provide a useful back up, especially for AE. As sensitivity and specificity are properties of the US diagnostic test they should not vary if the case mix reported in different studies remains the same. The use of the WHO standardised US classifications for CE and AE should be used so that the properties of the test are standardised. Quality control of field based studies will depend on geographical variations in the case mix and the relative proportions of cyst types without pathognomonic signs. The latter will have the most bearing on variations in specificity, as would the use of different classifications. Inter- and intra-observer variability and differences in prevalence will affect the performance of US in different endemic settings. Community based surveys must adhere to the highest ethical standards and the outcome of surveys should result in appropriate treatment and follow-up strategies for all infected individuals and suspected cases found during the surveys.

International classification of ultrasound images in cystic echinococcosis for application in clinical and field epidemiological settings

The increased knowledge of the natural history of cystic echinococcosis (CE) by the recent expansion in the use of ultrasound (US) in field and clinical studies has necessitated the development of a new WHO standardised classification of US images. Use of such a classification will enable clinicians to examine recommended clinical procedures for the different cyst types. It will also allow scientists to compare data on the occurrence of cyst types in different parts of the world providing evidence to examine strain differences in the causative organism Echinococcus granulosus. The classification proposed follows that of the first classification developed by Gharbi et al. [Radiology 139 (1981) 459] which has been widely used, but in modified forms, since its publication. The classification presented here is intended for use in field epidemiological studies as well as for clinical investigators. The classification is intended to follow the natural history of CE and starts with undifferentiated simple cysts, as presumably hydatid cysts evolve from these structures. These simple cysts, however, may be due to a number of different aetiologies (parasitic lesions, congenital disorders, biliary cysts or neoplasms) and, therefore, require further diagnostic tests to reveal their identity. As their origin is uncertain they are not given the designation of a CE type lesion, and, in the proposed classification, should be recorded as cystic lesions (CL). The first clinical group starts with cyst types CE 1 and 2 and such cysts are active, usually fertile cysts containing viable protoscoleces. CE Type 3 are cysts entering a transitional stage where the integrity of the cyst has been compromised either by the host or by chemotherapy and this transitional stage is assigned to the second clinical group. The third clinical group comprises CE Types 4 and 5 which are inactive cysts which have normally lost their fertility and are degenerative. The use of the standardised US classification will facilitate the application of uniform standards and principles of treatment currently recommended for each cyst type.