Antihelminthic Drugs used to treat parasitic worm infections: helminthic infections Unlike protozoa, helminthes are large and have complex cellular structures It is very important to identify the causative worm Done by finding the parasite ova or larvae in feces, urine, blood, sputum, or tissue Trematodes (flukes): E.g.: Blood flukes (schistosomiasis), fasciola. Cestodes (tapeworms): E.g.: Taenia Nematodes (roundworms, pinworm, whipworms and hookworms): E.g.: ascaris, filariasis, oxyuris (Enterobius vermicularis), Trichuris vulpis, Ancylostoma duodenale
Taeniasis / cysticercosis Taeniasis is the infection of humans with the adult tapeworm of Taenia saginata or T. solium. Humans are the only definitive hosts Two distinct life forms in human host, taeniasis (infection of gut lumen) & cysticercosis (infection of tissues with larval cysticercus form). It accounts for 10% of acute neurological admissions in endemic areas NEUROCYSTICERCOSIS. Length of adult worms is usually 5 m or less for T. saginata (however it may reach up to 25 m) and 2 to 7 m for T. solium.
CESTODES - TAPEWORM Segmented tape like worms with size varying from few mm to several meters. Adult worm consists of 3 parts: 1) Head(scolex) carrying grooved or cup like suckers, 2) Neck, immediately behind the head is the region of growth segments of body continuously generated. 3) Trunk, composed of chain of segments immature, mature & gravid.
Cestodes (Tape worms) Taenia saginata Acquired by eating uncooked beef meat Giant, several meters long Ova of T. saginata & T. solium are the same Adult worm live in Small Intestine Mainly asymptomatic Segments are passed with stools or seen on clothes Praziquantel is the drug of choice Niclosamide is also used Prevention: beef inspection & Cooking
Cestodes (Tape worms) Taenia solium & cysticercosis Acquired by eating uncooked pork meat. Smaller than saginata. Adult worm live in Small Intestine Mainly asymptomatic. Segments are passed with stools or seen on clothes. Praziquantel is the drug of choice for intestinal worms. Niclosamide is also used. Prevention: pork meat inspection & Cooking, personal hygiene to avoid autoinfection by ova which leads to cystcercosis.
Cestodes (Tape worms) Taenia solium & cysticercosis Cysticercosis: the larva acquired by ova autoinfetion or regurgitation from the adult worm in the intestine,may penetrate the stomach wall & go to develop as cysts in muscles, skin & brain (epilepsy, hydrocephalus). Diagnosis: ova in stool, CT & MRI for brain cysts, ELISA test for antibody detection. Treatment of cysticercosis is by praziquantel or albendazole combined with prednisolone to prevent brain edema & antiepileptic drugs are given to prevent fits until full recovery. Note - Hydrocephalus: water on the brain; CT: Computerized tomography
Life Cycle Eggs are passed with feces survive for days to months Cattle (T. saginata) and pigs (T. solium) become infected by ingesting vegetation contaminated with eggs. In the animal's intestine, the oncospheres hatch, invade the intestinal wall, and migrate to the striated muscles, where they develop into cysticerci. Humans become infected by ingesting raw or undercooked infected meat. In the human intestine, the cysticercus develops over 2 months into an adult tapeworm, which can survive for years.
The adult tapeworms attach to the small intestine by their scolex and reside in the small intestine and begins forming segments (proglottids) The proglottids which mature, become gravid, after two months of infection, gravid proglottids begin to detach from the distal end of tapeworm, and migrate to the anus or are passed in the stool (approximately 6 per day). Each segment contains 60,000 eggs The eggs contained in the gravid proglottids are released after the proglottids are passed with the feces Worm causes only minor inflammation to the intestine (mild symptoms - abdominal pain, distension, diarrhea and nausea - or none at all)
Human cysticercosis Larvae of T. solium (cysticercus cellulosae). T. solium has a complex two-host life cycle. Human beings are the only definitive host and harbour the adult tapeworm (taeniasis), whereas both humans and pigs can act as intermediate hosts and harbour the larvae or Cysticerci (cysticercosis). Humans infected following 1. Ingestion of T. solium eggs in water or vegetables. 2. Autoinfection & infection of close contacts by finger contamination with eggs from perianal skin or faeces of persons harbouring the adult worms.
Diagnosis-Taeniasis By demonstration of eggs, proglottids in stool. Mature proglottid of T. saginata, stained with carmine. Note the number of primary uterine branches (>12). Mature proglottid of T. solium, stained with carmine. Note the number of primary uterine branches (<13).
Diagnosis - cysticercosis Depends on the targeted organ: CNS - CSF immunology, neuro-imaging (CT/MRI) Viable cystecerci appear as rounded fluid collections, 1-2cm in diameter. Inflamed cysticerci has perilesional edema, contrast enhancement. Muscle - imaging, microscopic examination (invaginated scolex with suckers & hooks) Eye - imaging (ultrasound) (serological exam - ELISA) CSF: cerebro-spinal fluid CT: Computed tomography; MRI: magnetic Resonance Imaging
Treatment - taeniasis NICLOSAMIDE Second-line drug for treatment of most tapeworm infections. Adult (total 2g), children 2-6yrs, 1 g. Mechanism of action: Adult worm (not ova) is rapidly killed by inhibition of oxidative phosphorylation in mitochondria ATP depletion injured tape worms partly digested. Pharmacokinetics: Poorly absorbed from gut & excreted in urine. Clinical Uses Treatment of most forms of tapeworms. Not effective against cysticercosis or hydatic disease (echinococcosis). Given in the morning on empty stomach. Purgative is necessary to purge all dead segments & prevent liberation of ova.
Adverse effects & Contraindications Mild, infrequent and transitory GI disturbance Alcohol consumption should be avoided Not indicated in children under 2 years of age or in pregnancy. Praziquantel (10mg/kg) kills tape worm larvae. Acts by leakage of intracellular calcium from membranes. Used to treat trematodes, cestodes
Treatment - cysticercosis Use of antiparasitic agent (albendazole 15mg/kg/day BD x 28 days) plus simultaneous course of corticosteroids & antiepileptics