Cystic echinococcosis (CE), an infection with the larval form of the dog tapeworm Echinococcus granulosus, still causes serious lung and liver disease with a worldwide geographical distribution. This parasitic infection is preventable, eliminable, and treatable—in theory. The biological cycle can be attacked at various points: regular dog deworming, controlled sheep slaughtering, vaccination of the intermediate (sheep) animal host, and possibly in the future, vaccination of the definitive (dog) animal host (Figure 1). However, breaking the cycle in practice is difficult and requires long-lasting efforts. Control programs are expensive to set up and sustain. With the currently available options, a period of 20 years is needed to reach elimination, a goal that, unsurprisingly, has only been reached in rich countries .
At the current pace of control, patients suffering from CE will be seen for many decades to come. CE disease is chronic, complex, and neglected –. It is still poorly understood, and recommendations for diagnosis and treatment have not progressed beyond expert opinions and are not necessarily adopted by clinicians because of lack of grade I evidence.
The critical issues are:
1. CE may develop silently over years and even decades until it surfaces with signs and symptoms or as a chance finding on an ultrasound (US) scan or chest X-rays requested for unrelated reasons. Clinical manifestations may mean that the cyst is already complicated, e.g., ruptured into the biliary or bronchial tree, secondarily infected with bacteria, or leaking and causing allergic reactions if not anaphylactic shock.
2. Screening large samples of populations to detect asymptomatic cases is expensive. As with all screening procedures, ethical issues arise: do all patients in whom cysts are found require treatment? Is the treatment which we then offer well established and safe? And is it available at all? Screening projects in endemic areas are often inadequately prepared, as the clinical management is not provided locally for those who are found positive.
Problems start with the screening tool. With the exception of liver US, the available methods are far from satisfactory. In regards to serology, the sensitivity and specificity of several antigens have been well defined , , but available assays still lack standardization, sensitivity, and specificity . Controversies on the usefulness for clinical diagnosis and screening remain unresolved . Serodiagnostic performance depends on several factors, such as cyst location, cyst stage, and even cyst size, but these and other variables have not been thoroughly assessed to date.
Ultrasound is an indispensable tool, but will likely miss very small cysts, and its efficacy is mostly restricted to intraabdominal organs. Additionally, some cyst stages may be difficult to distinguish from non-parasitic cysts, which are common. The problem continues when an echinococcal cyst has been diagnosed. In settings where health care facilities are several days of travel away from the rural areas where patients live and work, and as long as we have doubts on what the natural evolution of their cysts will be, clinical decision making is difficult. It has to be done in each case individually based on current standards, clinicians' experience, and local technical possibilities, supported by embarrassingly poor evidence.
3. Not all CE patients are similar, even at a population level. Broadly speaking, there are two defined groups of patients, each with a different set of problems: mainly asymptomatic patients (detected in screening programs or by chance), or clinically apparent cases (mostly patients with complicated cysts).
(a) Patients with cysts detected during screening activities or as a chance finding. They mostly receive the treatment with which the attending clinician is familiar. This is not necessarily the best option relative to the cyst stage and clinical situation of the patient. Preliminary results from a survey on knowledge, attitudes, and practices regarding clinical management of CE in European, North African, and Middle Eastern countries yielded alarming results . Patients may be put at risk of interventions that may be completely unnecessary. This certainly applies to a sizeable number of cysts that have become inactive and do not cause any symptoms or complications.
A significant proportion of cysts stop growing and follow a path to spontaneous involution. Long-term follow-up suggests that these cysts and the patients harbouring them should be left alone. This is an appealing perspective for patients and health services, if evidence can be gathered in its support. CE4 and CE5 cysts appear to be very good candidates for this approach if they do not compromise any vital structures. It is, however, unclear if and under which circumstances this concept can be extended to other cyst types.
(b) Patients developing complications. Successful management depends on equipment, skills, and quality of available health services. The most common complications are biliary obstruction with or without cholangitis, bronchial obstruction, bacterial infection of the cyst cavity with abscess formation, rupture with anaphylactic reactions that range from mild to lethal anaphylactic shock, secondary echinococcosis (growth of new cysts caused by seeding of protoscolices, generally in a cavity such as the peritoneal space) following spillage of fluid from a cyst that ruptured either spontaneously or because of a therapeutic maneuver, and impaired function of organs and blood vessels compressed by growing adjacent cysts (Figure 2). In most endemic countries, the required setup is only met in major cities a long way off from where patients experiencing complications live.