**2. Epidemiology**

The most common form of hydatidosis is cystic echinococcosis caused by *E. granulosus*; it is present in several countries around the world and represents a major public health problem in some regions [9, 10]. It is considered endemic in areas such as Peru, Chile, Argentina, Uruguay, southern Brazil, the Mediterranean region, Central Asia, Western China, and East Africa [11]. Antarctica is the only continent free of this parasitic disease, and it has also been eradicated through efficient epidemiological control programs in Iceland, New Zealand, Tasmania, Falkland Islands, and Cyprus [12]. This pathology affects different organs, although the liver is the most commonly compromised, accounting for 70–75% of the cases. Alveolar echinococcosis caused by *E. multilocularis* is restricted to the Northern Hemisphere and might determine high morbidity and mortality [13]. Polycystic echinococcosis is caused by *E. vogeli* and only reported in Central and South America with low incidence rates [14]. Unicystic echinococcosis, caused by *E. oligarthrus*, is extremely rare in humans, and the only localization in which it has been reported is the orbit of the eye and the myocardium [15]. Other two species of the genus *Echinococcus*, *E. shiquicus* [16] and *E. felidis* [17], are present in the Tibetan Plateau and Africa, respectively, and there are investigations about risks of human affectation. In the South of Chile, cystic echinococcosis is an endemic zoonosis with an average incidence of 1.9/100,000 and a mortality rate of 0.2/100,000 inhabitants. The hospital discharge rate corresponds to 6.3/100,000, and this figure rises to 28.1/100,000 in our Araucanía Region [8].

## **3. Etiopathogeny**

Hydatidosis is caused by the larval stages of taeniid cestodes of the genus *Echinococcus*. There are nine species of this tapeworm currently identified, eight

**151**

**Figure 1.**

and scolices.

*Surgical Treatment of Hepatic Hydatidosis DOI: http://dx.doi.org/10.5772/intechopen.86319*

giving place to the formation of the hydatid cyst [22].

well-defined species and one genotypic cluster, that in future investigations could be defined as one to three different species. These nine species of *Echinococcus* are as follows: *E. granulosus* sensu stricto, *E. equinus*, *E. ortleppi*, *E. multilocularis*, *E. vogeli*, *E. oligarthrus*, *E. canadensis* cluster, *E. shiquicus*, and *E. felidis*. Each of them has a different life cycle, transmission routes, pathology forms of clinical presentation, possible human affectation, different geographical location, and biological behavior. Some of these species may affect humans, others only animals, and in others this is still unclear [18]. For example, regarding *E. shiquicus* and *E. felidis*, although they were known to infect only animals, there is growing apprehension about an eventual human affectation, and there is an ongoing research to support this with molecular and genomic studies [19, 20]. Other species of these parasites have exclusively wild life cycles. The study of their complex genotypic diversity aims to successfully prevent the transmission of this infection to humans [21]. The life cycle of these parasites starts with adult taeniid cestodes living in the small intestine of canids or felids (definitive host). Next, the adult tapeworms release their eggs, thus contaminating the feces, which are then ingested by rodents, ungulates, other herbivores, and occasionally humans (intermediate hosts). When humans are infected, the eggs reach the small intestine, and larval oncospheres hatch, which adhere and penetrate the intestinal mucosa by using their hooks and then migrate through the portal circulation to reach their first fixed location in the liver (50–70% of the cases). This happens most commonly in the right hepatic lobe due to the anatomical distribution of the portal venous system. The lungs are affected in 20–30% of the cases and much less frequently the spleen, kidneys, heart, muscles, bone, and central nervous system. For example, once located in the liver, the metacestodes begin their development and growth

The anatomical structure of the cyst has an outer acellular laminated membrane that allows the entry of nutrients from the host. Then there is the inner nucleated germinal membrane, in which the daughter vesicles are produced. In an asexual form, the protoscoleces are formed inside the daughter vesicles. The immunological system of the intermediate host reacts to isolate the parasite, forming a fibrous layer called adventitia, which can calcify with the passage of time (**Figure 1A**, **B**). The life cycle closes when the animal's definitive host is fed by contaminated viscera, and each protoscolece can develop an adult tapeworm in its small intestine [23] capsules

*(a) Hepatic solitary cyst, rounded, whitish external wall of uniform thickness. The cyst contains turbid liquid color upon formalin fixation and whitish yellowish germinal and laminated layer floating within the cyst. (b) The wall of the hydatid cyst has a laminated acellular membrane and a germinal layer with brood.*

#### *Surgical Treatment of Hepatic Hydatidosis DOI: http://dx.doi.org/10.5772/intechopen.86319*

*Liver Disease and Surgery*

**2. Epidemiology**

28.1/100,000 in our Araucanía Region [8].

with interaction of wild and domestic animals have been described as well. There are reported variants of these cycles depending on geographical location [4]. Cystic echinococcosis, the most common form of hydatidosis, is an endemic zoonosis caused by the larval stage (metacestodes) of the tapeworm *E. granulosus*. In relation to the geographical distribution, the disease is present in many countries around the world [5]. The diagnosis is supported by epidemiological history, anamnestic data, clinical presentation, radiological imaging, and serological tests. Surgical treatment employs different techniques, aiming for the best outcome for the patient. Partial cystectomy, pericystectomy, and hepatic resection are performed by either open or laparoscopic surgical access, with or without neoadjuvant or adjuvant medical therapy. There are also different procedures for the evacuation of the parasite, using percutaneous or endoscopic access. In selected cases, antiparasitic drug therapy is employed as the only treatment for this illness [6]. The prognosis for these patients will depend on the selection of the most adequate therapy according to several factors mainly related to the physical status of the patient and the larval stage of the parasite and its location [7]. Complicated cases must be treated in reference centers by well-trained and experienced hepatobiliary surgeons. This zoonosis has not yet been completely eradicated, and if affected countries do not apply epidemiological control policies, a great amount of resources will have to be allocated to the treatment of this illness. Cystic echinococcosis of the liver is endemic, especially in the South of Chile [8]. For this reason, the main theme of this chapter will be centered in topics concerning this form of hydatidosis.

The most common form of hydatidosis is cystic echinococcosis caused by *E. granulosus*; it is present in several countries around the world and represents a major public health problem in some regions [9, 10]. It is considered endemic in areas such as Peru, Chile, Argentina, Uruguay, southern Brazil, the Mediterranean region, Central Asia, Western China, and East Africa [11]. Antarctica is the only continent free of this parasitic disease, and it has also been eradicated through efficient epidemiological control programs in Iceland, New Zealand, Tasmania, Falkland Islands, and Cyprus [12]. This pathology affects different organs, although the liver is the most commonly compromised, accounting for 70–75% of the cases. Alveolar echinococcosis caused by *E. multilocularis* is restricted to the Northern Hemisphere and might determine high morbidity and mortality [13]. Polycystic echinococcosis is caused by *E. vogeli* and only reported in Central and South America with low incidence rates [14]. Unicystic echinococcosis, caused by

*E. oligarthrus*, is extremely rare in humans, and the only localization in which it has been reported is the orbit of the eye and the myocardium [15]. Other two species of the genus *Echinococcus*, *E. shiquicus* [16] and *E. felidis* [17], are present in the Tibetan Plateau and Africa, respectively, and there are investigations about risks of human affectation. In the South of Chile, cystic echinococcosis is an endemic zoonosis with an average incidence of 1.9/100,000 and a mortality rate of 0.2/100,000 inhabitants. The hospital discharge rate corresponds to 6.3/100,000, and this figure rises to

Hydatidosis is caused by the larval stages of taeniid cestodes of the genus *Echinococcus*. There are nine species of this tapeworm currently identified, eight

**150**

**3. Etiopathogeny**

well-defined species and one genotypic cluster, that in future investigations could be defined as one to three different species. These nine species of *Echinococcus* are as follows: *E. granulosus* sensu stricto, *E. equinus*, *E. ortleppi*, *E. multilocularis*, *E. vogeli*, *E. oligarthrus*, *E. canadensis* cluster, *E. shiquicus*, and *E. felidis*. Each of them has a different life cycle, transmission routes, pathology forms of clinical presentation, possible human affectation, different geographical location, and biological behavior. Some of these species may affect humans, others only animals, and in others this is still unclear [18]. For example, regarding *E. shiquicus* and *E. felidis*, although they were known to infect only animals, there is growing apprehension about an eventual human affectation, and there is an ongoing research to support this with molecular and genomic studies [19, 20]. Other species of these parasites have exclusively wild life cycles. The study of their complex genotypic diversity aims to successfully prevent the transmission of this infection to humans [21]. The life cycle of these parasites starts with adult taeniid cestodes living in the small intestine of canids or felids (definitive host). Next, the adult tapeworms release their eggs, thus contaminating the feces, which are then ingested by rodents, ungulates, other herbivores, and occasionally humans (intermediate hosts). When humans are infected, the eggs reach the small intestine, and larval oncospheres hatch, which adhere and penetrate the intestinal mucosa by using their hooks and then migrate through the portal circulation to reach their first fixed location in the liver (50–70% of the cases). This happens most commonly in the right hepatic lobe due to the anatomical distribution of the portal venous system. The lungs are affected in 20–30% of the cases and much less frequently the spleen, kidneys, heart, muscles, bone, and central nervous system. For example, once located in the liver, the metacestodes begin their development and growth giving place to the formation of the hydatid cyst [22].

The anatomical structure of the cyst has an outer acellular laminated membrane that allows the entry of nutrients from the host. Then there is the inner nucleated germinal membrane, in which the daughter vesicles are produced. In an asexual form, the protoscoleces are formed inside the daughter vesicles. The immunological system of the intermediate host reacts to isolate the parasite, forming a fibrous layer called adventitia, which can calcify with the passage of time (**Figure 1A**, **B**). The life cycle closes when the animal's definitive host is fed by contaminated viscera, and each protoscolece can develop an adult tapeworm in its small intestine [23] capsules and scolices.

#### **Figure 1.**

*(a) Hepatic solitary cyst, rounded, whitish external wall of uniform thickness. The cyst contains turbid liquid color upon formalin fixation and whitish yellowish germinal and laminated layer floating within the cyst. (b) The wall of the hydatid cyst has a laminated acellular membrane and a germinal layer with brood.*
