Comments
INITIAL SYMPTOMS:
Cystic mass most commonly in the liver or lungs; [CCDM]
EPIDEMIOLOGY:
The dog tapeworm, Echinococcus granulosus, causes cystic hydatid disease. Cysts take years to develop reaching diameters of 1-15 cm or more. Cysts are common in the liver and lungs. The differential diagnoses include cancer, amebic abscesses, and congenital cysts. The disease is most common in grazing areas of the world. Domestic dogs are hosts, and sheep are the intermediate hosts. Other intermediate hosts include cattle, goats, pigs, horses, moose, and caribou. Human infections usually occur in childhood after direct contact with the feces of infected dogs or indirectly through contaminated flies, fomites, food, or water. "Dogs become infected by eating animal viscera containing hydatid cysts and begin to pass eggs 5-7 weeks later. Most canine infections resolve spontaneously by 6 months;" [CCDM, p. 180-1] Ultrasound prevalence surveys have shown population infection rates as high as 6.6%. [Cecil, p. 2055] Strains that infect cattle, moose, elk, and deer are more benign, affecting mainly the lungs. [ABX Guide]
FINDINGS:
Cysts are found in the liver, lung, or other organs. Bile obstruction may occur and cause jaundice. Rupture of a cyst, depending upon its location, may cause fever, urticaria, abdominal pain, cough, chest pain, dyspnea, and hemoptysis. [Merck Manual, p. 1362] E. granulosa forms cysts in the liver 50% to 70% of the time, in the lung 20% to 30% of the time, and in other organs 10% of the time. Cysts can reach a size of 5-10 cm within one year. Cyst rupture can cause severe allergic reactions including anaphylaxis. Serology assays are available from the CDC to confirm past exposure when suspicious cysts are found by MRI, CT, or ultrasound. [PPID, p. 3233-4] Echinococcus cysts can cause secondary myelitis--pain at the spinal cord level aggravated by coughing with asymmetric paresthesias and weakness below the level of the lesion. [ID, p. 1360] Hematuria is a sign of renal cysts. [Guerrant, p. 828] Rupture into the biliary tree can cause jaundice, cholangitis, and pancreatitis. A growing cyst in the liver can cause pain, jaundice, nausea & vomiting, and eventually biliary cirrhosis. Rupture of a cyst can also cause anaphylactic shock or septic shock. [Cohen, p. 1184-5] Nodular skin lesions may occur. [Guerrant , p. 963]
RELATED INFECTIONS:
The two other major forms of echinococcosis are alveolar (E. multilocularis) and polycystic (E. vogeli and E. oligarthrus). Alveolar echinococcosis may mimic hepatic carcinoma or cirrhosis. The name "alveolar" refers to the lung-like appearance of the budding mass. In contrast with E. granulosus, there are no cyst walls. Cysts grow into tumor-like masses. Common symptoms are right upper quadrant pain, malaise, and weight loss. Both E. granulosa and E. multilocularis can form cysts in the eye. The disease is widely distributed in the northern hemisphere and is maintained by a fox-rodent cycle. Dogs and, less often, cats may become definitive hosts after eating infected rodents. Serological tests are sensitive and specific. Common symptoms are right upper quadrant pain and weight loss. Treatment and prevention are similar to that for E. granulosa. [Guerrant, p. 824-38, 1015] Humans are infected accidentally after ingestion of ova-contaminated soil. [Cecil, p. 2057] Other intermediate hosts are pigs, wild boars, dogs, and monkeys. [ABX Guide]
Polycystic echinococcosis is a disease of South and Central America caused by E. vogeli (over 100 cases reported) or E. oligarthus (only a few cases reported). Like the other echinococcus species, infections occur primarily in the liver, but also in the lungs and other tissues. E. vogeli is maintained in a cycle of infection between bush dogs and paca. Domestic dogs may become definitive hosts. E. oligarthus is the only species of Echinococcus in which wild cats are the definitive hosts. [Guerrant, p. 824-38, 1015]
For updated text and symptoms of infectious diseases, see iddx.com.