Taenia and Echinococcus infections in humans.
Important human tapeworms include Taenia solium, T. saginata, T. asiatica, Echinococcus granulosus and E. multilocularis. Their morphology and reproductive powers are the basis for their survival in the intestine.
Taeniasis and cysticercosis
Human cysticercosis may result from the ingestion of the eggs of Taenia species, particularly T. solium. Gastrointestinal tapeworm infections result from the ingestion of cysticerci in undercooked meat.
Human cysticercosis with T. solium is common in central and South America, South East Asia, eastern and southern Africa. (1,2) In South Africa, the Eastern Cape Province has the highest prevalence owing to the common practice of free-range pig farming and improper sanitation facilities. (2)
Damage depends on the site and number of cysticerci that develop. (1) Infection commonly occurs in the brain (neurocysticercosis), causing seizures, hydrocephalus or focal neurological deficits. Damage from cysticercosis is caused by the severe inflammatory response occurring after the death and disruption of the parasite. (1) Muscles, subcutaneous tissues and the eye may also be affected. (1)
Diagnosis is based on serology, using the enzyme-linked immunosorbent assay (ELISA), although the enzyme-linked immunoblot assay performs much better than the ELISA in clinical settings. The presence of eosinophils in the cerebrospinal fluid may also suggest the diagnosis. (1) Plain radiographs of soft tissues demonstrate the oval or elongated cysts if they are wholly or partially calcified. Plain skull films may show cerebral calcifications. Computed tomography imaging may demonstrate calcified and non-calcified cysts, oedema or intracranial hypertension. (1)
Cysticercosis may require surgery for ophthalmic or brain involvement, but chemotherapy should precede surgery when possible. Tissue infection can be treated with albendazole or praziquantel (combined with corticosteroids in the case of extensive disease to reduce the inflammatory response to the dead cysticerci. Steroid use should be considered when treating non-calcified cerebral cysts). Seizures respond well to anti-epileptic drugs. (1)
On the other hand, T. saginata is transmitted as cysticerci in partially cooked or raw beef. T. asiatica is found in South East Asia, with pigs being the possible intermediate host. (3)
Symptoms are similar for T. saginata and T. asiatica infections. (3) These include nausea or vomiting, appetite loss, abdominal pain, and weight loss. A disturbing manifestation is the active crawling of the muscular segments out of the anus. (3)
Diagnosis of Taenia species can be made by examination of the number of outpocketing branches of the uterus in the gravid segments, because the eggs are identical. (1) Perianal scraping with adhesive tape is highly sensitive for T. saginata but not for T. solium. Coproantigen-detection ELISA may be used to identify Taeniaspecific molecules in faecal samples, demonstrating current infection. (1) Treatment includes the administration of niclosamide or praziquantel.
E. granulosus is common in sheep-raising areas of southern South America, southern and central Russia, East Africa, and the western USA. (4) Many South African cases have been described. A history of rural sheep farming should raise concerns about hydatid disease.
Dogs and sheep are the only final hosts in which the adults are found; humans are the dead end in the cycle. (4) Echinococcosis (hydatid disease) develops when humans ingest eggs that then hatch in the intestine. Larvae develop, penetrating the intestine, disseminating throughout the body, and concentrating mainly in the liver, but also in the lungs, heart, brain, kidneys, and long bones. (4)
Infected patients may be asymptomatic for many years, but pressure effects eventually develop depending on the site of the hydatid, resulting in collapse of infected parts of the long bones, blindness, and seizures. Rupture of a hydatid cyst may result in anaphylaxis. (4)
Isolated hooks in the sputum suggest rupture of a lung cyst. Serological tests include indirect haemagglutination, latex agglutination or an ELISA. (4) Ultrasound, magnetic resonance and computed axial tomography imaging may demonstrate deep-seated lesions and avascular fluid-filled cysts. (4)
Treatment is mainly by surgical resection. Long courses of albendazole or mebendazole have proved effective, although the results are variable. Percutaneous puncture under sonographic guidance, aspiration of cyst fluid, instillation of a protoscolecidal agent such as 95% methanol or cetrimide, and respiration (PAIR), with albendazole treatment to reduce the danger of subsequently renewed disease from spillage, is an alternative to surgical resection in selected patients and is particularly indicated in uncomplicated single hepatic hydatid cysts.
E. multilocularis normally follows a fox-rodent cycle in northern Siberia, China, Japan and North America. The primary cyst usually forms in the liver. Early radiological imaging by ultrasonography, computed tomography, or magnetic resonance is essential. Serological tests with purified E. multilocularis antigens are sensitive and highly specific. Treatment includes long-term albendazole, and surgery. (4)
Infection of the immunocompromised host
Cestode infections should be considered as differential diagnoses of co-infections in HIV/AIDS patients. (5) Little information is available on clinical features, treatment, and outcome of patients in South Africa, where a high prevalence of HIV infection and a large immigrant population exist.
Patients with AIDS are expected to have disease that develops rapidly and manifests early, although symptoms vary depending on the organ involved and the degree of immune deficiency. T. solium infection in HIV-infected patients commonly manifests as neurocysticercosis, while hydatid disease presents with cystic lesions in the liver and lungs. (5,6)
Careful consideration of drug interactions that may occur with antiretroviral therapy and the likelihood of the immune reconstitution syndrome (IRIS) developing make the management of such patients challenging. (5)
(1.) Garcia H, Gonzalez A, Evans C, et al. Taenia solium cysticercosis. Lancet 2003; 362: 547556.
(2.) Mafojane N, Appleton C, Krecek R, Michael L, Willingham A. The current status of neurocysticercosis in Eastern and Southern Africa. Acta Trop 2003; 87: 25-33.
(3.) Ito A, Nakao M, Wandra T. Human taeniasis and cysticercosis in Asia. Lancet 2003; 362: 1918-1920.
(4.) McManus D, Zhang W, Li J, Bartley P. Echinococcosis. Lancet 2003; 362: 1295-1304.
(5.) Chopdat N, Menezes CN, John MA, Mahomed N, Grobusch MP. A gardener who coughed up blood. Lancet 2007; 370(9597): 1520.
(6.) Serpa J, Moran A, Goodman J, Giordano T, White A. Neurocysticercosis in the HIV era: A case report and review of the literature. Am J Trop Med Hyg 2007; 77: 113-117.
Colin Nigel Menezes, MD, MMed (Int Med), Dip HIV Mang (SA), DTM&H, FCP (SA) Consultant, Infectious Diseases Unit and Themba Lethu Clinic, Department of Internal Medicine, Helen Joseph Hospital, University of the Witwatersrand, Johannesburg
Martin Peter Grobusch, MD, MSc, DTM&H Professor, Division of Clinical Microbiology and Infectious Diseases, National Health Laboratory Service and School of Pathology, Faculty of Health Sciences, University of the Witwatersrand, Johannesburg
Corresponding author: Colin Menezes (Colin. Menezes@wits.ac.za)