Tropical Parasitic Infestations

Ascaris lumbricoides

The roundworm Ascaris lumbricoides is the most common helminthic infestation in the world, infecting over 1 billion people. Cases have been reported from nonendemic areas in both developing and developed countries.

The infestation is usually asymptomatic. A. lumbricoides organisms normally reside in the jejunum but are actively motile and can invade the papilla, migrating into the bile duct and causing biliary obstruction, with a variety of hepatobiliary complications, including biliary colic, pancreatitis, cholecystitis, postcholecystectomy syndrome, hepatic abscess, and hepatolithiasis. Ascariasis has also been reported to cause obstruction of a biliary self-expandable metal stent. Identification of parasite DNA in biliary stones suggests that Clonorchis sinensis and A. lumbricoides may predispose to biliary stone formation and recurrent pyogenic cholangitis (RPC). Over 5% cases of hepatobiliary ascariasis develop RPC and 10% of patients with RPC have definite evidence of ascariasis.

Biliary-pancreatic ascariasis is commonly reported in high-endemic regions such as the Kashmir valley in India. In a study of 500 patients with hepatobiliary and pancreatic ascariasis, Khuroo et al. reported biliary colic in 56%, acute cholangitis in 24%, acute cholecystitis in 13%, acute pancreatitis in 6%, and hepatic abscess in less than 1%. Biliary-pancreatic ascariasis should be suspected in patients from an endemic area presenting with biliary symptoms.

In this setting, identification of eggs, larva, or the adult worm from bile or feces is strongly suggestive of the disease. Ultrasonography is the imaging modality of choice for diagnosis and follow-up of patients with hepatobiliary ascariasis. Characteristic sonographic findings include thick echoic stripe with a central, longitudinal anechoic tube (gastrointestinal tract of the worm; inner tube sign), thin nonshadowing strip without an inner tube (strip sign), overlapping longitudinal interfaces in the main bile duct (spaghetti sign), and the characteristic movement of these long echogenic structures within the bile duct.

In cases where ultrasonography is nondiagnostic, endoscopic ultrasonography (EUS) and magnetic resonance cholangiopancreatography (MRCP) may be performed. By EUS, worms appear as a long linear hyperechoic structure without acoustic shadowing (“single-tube” sign) or with central hypoechoic tube (“double-tube” sign).

ERCP and Endotherapy for Hepatobiliary Ascariasis

Endotherapy is indicated if there is no clinical improvement after intensive medical management is administered and if the worm is known to persist in the ductal lumen up to 3 weeks after therapy. During endoscopy, worms can be seen in the duodenum and are often seen protruding from the ampulla of Vater. During ERCP, cholangiographic features of the Ascaris worm include the presence of long, smooth, linear filling defects with tapering ends ( Fig. 49.1 ); smooth, parallel filling defects; curves and loops crossing the hepatic ducts transversely; and dilatation of bile ducts (usually the common bile duct). With the recent availability of the SpyGlass direct visualization system (Boston Scientific, Marlborough, MA), the worm can also be visualized directly within the bile duct. Endoscopy is the mainstay of treatment for biliary ascariasis.

Worm extraction is easy when the worm protrudes out of the ampulla of Vater ( Fig. 49.2 ). The worm can be held with a grasping forceps and slowly brought out by withdrawing the endoscope out of the patient. A Dormia basket can also be used to maneuver the outer end of the worm into the strings of the basket and gently hold it before it is extracted.

It is best to avoid using a polypectomy snare for a protruding worm, as it tends to cut the worm. Remnant worms can lead to stone formation, and all efforts must be made to ensure complete removal. Worms within the common bile duct occasionally protrude out of the papilla after contrast injection. Alternatively, they can be extracted using a Dormia basket or a biliary occlusion balloon.

It has been postulated that endoscopic sphincterotomy should be avoided in endemic areas, in view of the high reinfestation rates and easy entry of worms into postsphincterotomy bile ducts. In a study including more than 300 patients, Sandouk et al. suggested that pancreaticobiliary ascariasis was more common in patients with prior cholecystectomy or sphincterotomy. On the other hand, Alam et al. needed a wide sphincterotomy in 94.8% of the 77 patients with pancreaticobiliary ascariasis in their study but did not report any major adverse event or recurrence after sphincterotomy.

Similarly, Bektas et al. did not report any recurrence of biliary ascariasis in their patients after sphincterotomy. Ascariasis may coexist with biliary calculi or strictures. In these situations, endoscopic balloon dilation of the biliary sphincter (sphincteroplasty) is an alternative to sphincterotomy to retrieve the parasite and associated calculi. In endemic areas, pregnant women are prone to develop biliary ascariasis. Endoscopic intervention in such cases requires special precautions, including lead shielding of the fetus and limitation of total fluoroscopic exposure (see Chapter 3 ). Failure of endoscopic extraction may require surgical extraction, which has increased risks of fetal wastage and premature labor.

Extraction of the culprit worm is usually associated with rapid symptom relief and is successful in more than 80% of patients.

However, infection may be associated with calculi or strictures, which can usually be dealt with endoscopically. After endoscopic therapy, all patients should receive antihelminthic therapy to eradicate remaining worms. A single dose of albendazole (400 mg) is highly effective against ascariasis. In endemic areas, periodic deworming may have a role in preventing recurrences.

Echinococcus granulosus

The “domestic” strain of Echinococcus granulosus is the main cause of human hydatid disease. Infections are found worldwide and remain endemic in sheep-raising areas. The life cycle involves two hosts: the adult tapeworm is usually found in dogs (definitive host), whereas sheep (intermediate host) are the usual host for the larval stages. Human exposure is via the oral–fecal route with food or water contaminated by the feces of the infected definitive host, usually a dog.

Embryonated eggs hatch in the small intestine and liberate oncospheres that migrate to distant sites. The right lobe of the liver is the most common site for hydatid cyst formation. The majority of patients remain asymptomatic. In symptomatic patients, abdominal ultrasonographic and serologic studies usually establish the diagnosis.

In approximately one-fourth of cases, hydatid cysts rupture into the biliary tree, causing obstructive jaundice.

Contents of the cyst (the scolices and daughter cysts) draining into the biliary ducts cause intermittent or complete obstruction of the bile duct, resulting in obstructive jaundice, cholangitis, and sometimes cholangitic abscesses. Rarely, acute pancreatitis complicates intrabiliary rupture of a hydatid cyst.

Cysto-biliary communication is common, occurring in 10% to 42% of patients, and is often recognized at surgery when cysts are stained with bile. Unrecognized cysto-biliary communication may present in the postoperative period as a persistent biliary fistula, resulting in prolonged hospitalization, and can increase morbidity.

Hydatid cyst involving the pancreatic head and body has been rarely reported. These cysts can enlarge and may manifest as acute pancreatitis, chronic pancreatitis, or obstructive jaundice, and easily confused with pancreatic pseudocysts, tumors, or other congenital pancreatic cysts. Surgical intervention is generally required for management.