Echinococcosis includes hydatid or unilocular cyst disease, caused by Echinococcus granulosus (the minute dog tapeworm) or Echinococcus vogeli, and alveolar cyst disease, caused by Echinococcus multilocularis (Table 123-4). Dogs become infected with tapeworms by eating infected sheep or cattle viscera and excrete eggs in their stools. Humans acquire echinococcosis by ingesting eggs and become an intermediate host. The eggs hatch in the intestinal tract, and the larva (oncospheres) penetrate the mucosa and enter the circulation to pass to the liver and other visceral organs, forming cysts 2 cm in diameter.
E. granulosus has a worldwide distribution and is endemic in sheep-raising and cattle-raising areas of Australia, South America, South Africa, the former Soviet Union, and the Mediterranean region. The prevalence is highest in children. Symptoms caused by E. granulosus result from space-occupyingcysts. Pulmonary cysts may cause hemoptysis, cough, dyspnea,and respiratory distress. Brain cysts appear as tumors; livercysts cause problems as they compress and obstruct blood flow.Ultrasonography identifies cystic lesions, and the diagnosis isconfirmed by serologic testing. Large or asymptomatic granulosa cysts are removed surgically. Treatment with albendazolehas shown some benefit.
Neurocysticercosis is caused by infection with the larval stages (cysticerci) of the pork tapeworm, Taenia solium, and is the most frequent helminthic infection of the CNS (see Table 1234). Humans are infected after consuming cysticerci in raw or undercooked larva-containing pork. T. solium is endemic in Asia, Africa, and Central and South Americas.
Cysts typically enlarge slowly, causing no or minimal symptoms for years or decades until the organism begins to die. The cyst then begins to swell, and leakage of antigen incites an inflammatory response, resulting in the presenting signs of focal or generalized seizures and calcified cerebral cysts identified by computed tomography or magnetic resonance imaging. The CSF shows lymphocytic or eosinophilic pleocytosis. The diagnosis is confirmed by serologic testing. Neurocysticercosis is treated with albendazole or praziquantel, corticosteroids for concomitant cerebral inflammation from cyst death, and anticonvulsant drugs.
Mycobacterium tuberculosis are pleomorphic, weakly gram-positive curved rods. Mycobacteria are acid fast, which is the capacity to form stable mycolate complexes with arylmethane dyes. Mycobacteria grow slowly; culture from clinical specimens on solid synthetic media usually takes 3 to 6 weeks. Drug-susceptibility testing requires an additional 4 weeks. Growth can be detected in 1 to 3 weeks in selective liquid media using radiolabeled nutrients. Polymerase chain reaction (PCR) of clinical specimens allows rapid diagnosis in many laboratories.
An estimated 10 to 15 million persons in the United States have latent tuberculosis infection (infection with M. tuberculosis and no disease). Without treatment, tuberculosis disease develops in 5% to 10% of immunologically normal adults with tuberculosis infection at some time during their lives; the risk is higher in infants. An estimated 8 million new cases of tuberculosis occur each year among adults worldwide. Three million deaths are attributed to the disease annually. In developing countries, 1.3 million new cases of the disease occur in children under 15 years of age, and 450,000 children die each year of tuberculosis. Most children with tuberculosis infection and disease acquire M. tuberculosis from an infectious adult.