Ensayos de Flexión de Dedos

Large intestinal tapeworms (except for Taenia solium)

Taeniasis saginata is caused by the adult cestode Taenia saginata, or beef tapeworm, and humans are the definitive hosts. Adult cestodes are harbored in the small intestine. Individual worms are 5-8 m long and are composed of a chain of 1000-2000 proglottides which, when gravid, are expelled in feces. T. saginata is distributed worldwide and infestation is common in Ethiopia and in Mexico, and relatively common in South America and East and West Africa. It rarely produces severe clinical features, but must be distinguished from taeniasis caused by T. solium.

Diphyllobothriasis infestation is with the adult cestode Diphyllobothrium latum, or fish tapeworm. The infestation occurs in most parts of the world (e.g. Europe, the Near East, Siberia, Japan and North America). People become infested from eating poorly cooked fillets of salmon, trout and pike, which are intermediate hosts. The adult cestode is the longest human tapeworm (4-10 m in length). Most patients are asymptomatic, but in Finland some patients with this disease are anemic owing to a lack of vitamin B12.

page 157 page 158

The above infestations with large cestodes can be treated with praziquantel, niclosamide, or Gastrografin.

PRAZIQUANTEL

Before treatment, the patient is given a laxative electrolyte solution (e.g. GoLytely, a polyethylene glycol lavage solution) to reduce the fecal mass. Praziquantel is then given as a single oral dose of 10 mg/kg. Magnesium sulfate is taken 2-3 hours later as a rapid-acting laxative to expel the cestode.

NICLOSAMIDE

Niclosamide is a halogenated salicylamide introduced in the 1960s and is no longer approved in the USA. Its anthelminthic action involves stimulation of cestode oxygen uptake at low concentrations and blocking cestode glucose uptake at higher concentrations. When the cestode dies, the scolex is released from the intestinal wall and the worms are digested. With T. solium infestations, ova released from the gravid eggs can cause dangerous cysticercosis.

Niclosamide is a cheap, effective and readily available in much of the world. Little is absorbed from the gastrointestinal tract. On the day of treatment, the patient is fasted. The adult dose is 2 g and less is given to children. The tablets should be chewed thoroughly before swallowing and washed down with a little water. Post-treatment purges to expel the worm are not necessary because the scolex and proglottides may be digested as a result of the effect of this drug.

Adverse effects of niclosamide are not severe, though mild gastrointestinal disturbances can occur.

GASTROGRAFIN

Gastrografin is a water-soluble contrast material used to reveal the gastrointestinal tract for radiography. It has been shown to have an anthelminthic effect on intestinal cestodes (T. saginata, D. latum, Diplogonoporus grandis) although the mechanism of its anthelminthic action has not been reported. It is given after a laxative solution. Gastrografin (300 ml) is injected through a duodenal tube inserted through the mouth until the tip reaches the duodenal flexure. Under fluoroscopic monitoring, the tapeworms are evident as radiolucent shadows. When the parasites reach the rectum, the patient is encouraged to defecate.

Taeniasis solium and cysticercosis cellulosae

Taenia solium, the pork tapeworm has a worldwide distribution. The adult cestode lives in the human intestine, like T.

saginata and D. latum, possesses 800-900 proglottides and measures 2-3 m in length. The life cycle of T. solium is illustrated in Figure 6.31.

Cysticercosis is caused by the larvae of T. solium (Cysticercus cellulosae), which live subcutaneously in the muscle, orbit and brain. Most cases result from ingestion of food and water contaminated with the eggs of T. solium. Taeniasis

solium and cysticercosis occur in Latin America, Eastern Europe, India, Pakistan, Indonesia, China and Korea. The clinical manifestations of cerebral cysticercosis depend on the location of the cyst.

Figure 6.31 The life cycle of the cestode Taenia solium on its journey from pig to man.

▪ The drugs used to treat taeniasis solium and cysticercosis include Gastrografin, praziquantel and albendazole

Gastrografin is the drug of choice for taeniasis because it does not damage the cestode. Damage to the cestode releases dangerous live eggs of T. solium into the intestinal lumen. The anthelminthic action and dose for therapeutic use of Gastrografin are as above.

Cysticercosis is treated only after Gastrografin to remove the tapeworm. Praziquantel and albendazole are used.

Praziquantel is administered in a daily oral dose of 75 mg/kg, divided into three portions, for 7 days. After a further 7 days, it is given again at the same dose. Prednisolone is given throughout the treatment period to prevent or reduce allergic reactions that may result from the destruction of the cysticerci.

Albendazole is used for treating cysticercosis (and hydatid disease, see below). Albendazole is absorbed from the gastrointestinal tract and is rapidly and extensively metabolized in the liver. It is recommended that it be taken on an empty stomach when it is used against intestinal cestodes, but with a fatty meal when used against tissue cestodes.

Two 7-day courses of 10-15 mg/kg/day divided into three portions are separated by treatment-free periods of 7 days.

Prednisolone is also given throughout treatment to reduce allergic reactions.

Adverse effects of albendazole include transient gastrointestinal discomfort and headache.

Echinococcosis (hydatid disease)

▪ Echinococcosis is caused by the larval forms of the cestodes Echinococcus granulosus and E. multilocularis, and is acquired by ingestion

page 158 page 159

Echinococcus granulosus is found worldwide and echinococcosis (cystic hydatid disease) occurs in East Africa, the Mediterranean littoral, South America, the Middle East, Australia, India and Russia. E. multilocularis is the second most common species. Echinococcosis from E. multilocularis (alveolar hydatid disease) occurs in Canada, Central Europe, Siberia, Alaska and northern Japan. The adult cestodes of E. granulosus and E. multilocularis measure 2-7 mm and 1.2-4.5 mm in length, respectively. The adult cestodes live in the small intestine of a final host (e.g. dog, fox, wolf). Humans are the intermediate hosts, and ingest the eggs excreted by an infested final host. The clinical

manifestations depend on the size of the cyst (E. granulosus) and the degree of infestation (E. multilocularis) in the liver, lung and other organs. Echinococcosis from E. multilocularis resembles carcinoma in its ability to metastasize and is frequently fatal.

Surgery is still the treatment of choice for operable cases of echinococcosis. Chemotherapy with oral albendazole can be effective, given as four 30-day courses of 10-15 mg/kg/day divided into three portions separated by treatment-free periods of 15 days.

Hymenolepiasis

Hymenolepiasis is caused by Hymenolepis nana (the dwarf tapeworm) and H. diminuta. The latter is the smallest cestode in humans. It measures 1-4 cm, and commonly infects children in tropical and subtropical regions. The infestation is acquired by ingesting the worm's eggs contaminating food and water. Autoinfestation and rapid cestode reproduction increase the infestation in malnourished or immunocompromised children, who experience

gastrointestinal manifestations including nausea, vomiting, diarrhea and abdominal pain.

H. diminuta is a common parasite of rats and mice that occasionally infests humans. The adult cestode measures 20-60 cm in length. Its life cycle requires an intermediate host (fleas) and a final host (rats and mice). People acquire the infestation by accidentally ingesting infected fleas.

Treatment is with praziquantel administered as a single dose of 10-25 mg/kg. Niclosamide can be used for H. nana infestations

Some of the antiparasitic drugs and the diseases for which they are used are summarized in Table 6.29.

Table 6-29. Drugs for the treatment of parasitic infections either as primary, secondary or combination therapy (not all available in the USA)

Drug Infection(s) Drug Infection(s)

Albendazole Strongyloidiasis Metronidazole Amebiasis, giardiasis, trichomoniasis

Cysticercus cellulosae American trypanosomiasis (Chagas' disease)

Echinococcosis (hydatid

disease) Pentamidine

isethionate African trypanosomiasis, pneumocystosis

Amodiaquine Malaria Piperazine Ascariasis (roundworm)

Antibiotics (clindamycin, tetracycline,

doxycycline)

Malaria Praziquantel TREMATODES (schistosomiasis,

clonorchiasis, opisthorchiasis, Eflornithine African trypanosomiasis Pyronaridine Malaria

Gastrografin Taenia saginata and T.

solium

Quinidine Malaria

Halofantrine Malaria Quinine Malaria

Ivermectin NEMATODES

Tafenoquine Malaria

Thiabendazole Strongyloidiasis, nematode larval

infections

Meglumine antimoniate Leishmaniasis Tinidazole Amebiasis, giardiasis, trichomoniasis Melarsoprol African trypanosomiasis Triclabendazole Fascioliasis

page 159 page 160

FURTHER READING

Baird JK. Effectiveness of antimalarial drugs. N Engl J Med 2005; 352: 1565-1577.

Barrett MP, Burchmore RJ, Stich A et al. The trypanosomiases. Lancet 2003; 362: 1469-1480.

Docampo R, Moreno SN. Current chemotherapy of human African trypanosomiasis 2003; 90(Suppl): 10-13.

Greenwood BM, Bojang K, Whitty CJ, Targett GA. Malaria. Lancet 2005; 365: 1487-1498.

Horton J. Global anthelmintic chemotherapy programs: learning from history. Trends Parasitol 2003; 19: 405-409.

Murray J, Berman C, Davies N, Saravia. Advances in leishmaniasis. Lancet 3656: 1561-1577H.

Olliaro PL, Taylor WR. Antimalarial compounds: from bench to bedside. J Exp Biol 2003; 206: 3753-3759. [A review of antimalarial drugs.]

Petersen E. Malaria chemoprophylaxis: when should we use it and what are the options? Expert Rev Anti Infect Ther 2004; 2: 119-132.

[Antimalarial coverage for those not normally exposed to malaria.]

Stanley SL. Amoebiasis. Lancet 2003; 361: 1025-1034. [A comprehensive overview of the use of drugs and for amoebic infections.]

Strickland GT (ed.) Hunter's Tropical Medicine and Emerging Infectious Diseases, 8th edn. Philadelphia: W.B. Saunders; 2000. [This textbook describes general aspects of tropical and parasitic diseases and their treatment.]

Upcroft P, Upcroft JA. Drug targets and mechanisms of resistance in the anaerobic protozoa. Clin Microbiol Rev 2001; 1: 150-164.

Wilairatana P, Krudsood S, Treeprasertsuk S, Chalermrut K, Looareesuwan S. The future outlook of antimalarial drugs and recent work on the treatment of malaria. Arch Med Res 2002; 33: 416-421. [Malarial resistance and how to combat it in the future.]

WEBSITES

Van Voorhis, WC, Weller PF. Chapters XXXIV Protozoan infections and XXXV Parasitic infections. In: ACP Medicine. Web MD Inc. 2005.

Centers for Disease Control

http://www.cdc.gov/ncidod/srp/drugs/drug-services.html [Information on antiparasitic drugs.]

WHO

http://www.who.int/tdr [Details on the WHO program for tropical diseases.]

http://www.malaria.org/ [This website provides general information about malaria.]

http://www.nlm.nih.gov/medlineplus/parasiticdiseases.html [Provides general information regarding parasites and antiparasitic drugs.]