Parasitology - Viviparous Roundworms

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These roundworms release live larvae ("viviparous") instead of laying eggs

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Trichinella, Dracunculus (guinea worm), Filarial infections (elephantiasis, river blindness, eye worm)

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Transmission of this worm is from carnivore (or ominovore) to carnivore by eating skeletal muscle from the previous host

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Trichinella

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This infection features encysted larval progency in skeletal muscle

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Trichinella

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This worm is acquired by eating undercooked pork (or any other carnivore)

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Trichinella

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Route of invastion of Trichinella

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Meat (animal muscle) with encysted larva is eaten, larva are released in small intestine, where they invade the mucosa and mature

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Infective stage of Trichinella

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Larva within meat

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How long after infection by Trichinella does fertilization take place?

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2 days

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How long after infection by Trichinella are live larvae released?

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5 days

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How long does the Trichinella worm continue to release larvae?

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1 month

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How long do Trichinella larvae take to reach maximal size in the muscle?

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3 weeks

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Survival time of Trichinella larvae in smooth muscle

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2 years (after which time they die and are calcified)

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Diagnostic stage of Trichinella

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Encysted larva in striated muscle

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The diagnostic and infective stages of this worm are the same

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Trichinella (encysted larva in striated muscle)

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What happens to the Trichinella cyst over time?

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It becomes calcified

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Clinical signs and symptoms of Trichinella early on in heavy infection

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Diarrhea, gastroenteritis

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Cause of death in Trichinella

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Migration of larvae to heart and brain

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Clinical signs and symptoms of Trichinella later on in heavy infection

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Eosinophilia, periorbital edema, diplopia, muscle pain, headache, fever, others (a wide array is possible)

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Various serological tests support diagnosis of infection by this roundworm

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Trichinella

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Treatment of Trichinella

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Steroids may be useful; bendazole is recommended but is not proven effective

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Prevention of Trichinella

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Cook meat, freeze meat (several days); at the population level, stop feeding uncooked pork scraps (via garbage) to pigs

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T/F: In the US, it is illegal to throw out raw pork

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True. Risk of worm transmission (eg, trichinella)

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Geographic distribution of Trichinella

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Worldwide, except Australia and some Pacific Islands

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Genus of roundworm that causes Guinea Worm

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Dracunulus (Guinea worm)

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Transmission of Guinea worm

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Copepods in drinking water containing infectious larvae

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Intermediate host of Dracunulus (Guinea worm)

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Copepod (tiny crustacean)

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The female of this worm type grows to 1 m long

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Dracunulus (Guinea worm)

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Diagnostic stage of Dracunulus

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Larva or adulte female escaping from skin in response to submersion of ulcer in cold fresh water

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Infective stage of Dracunulus

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Larva (third stage larva)

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Dracunulus (guinea worm) prefers to migrate in subcutaneous tissue, especially in this part of the body

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Legs

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Life cycle of guinea worm (Dracunulus)

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Infectious larvae are ingested then penetrate the intestinal wall and enter connective tissue or body cavities where the male and female mate. The female then migrates to superficial cutaneous tissue where she gives birth to live larvae which then escape through the skin

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This worm gives birth by prolapse of the uterus in response to submersion in fresh water

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Dracunulus (Guinea worm)

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Definitive host of guinea worm (Dracunulus)

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Human

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If this worm is broken during treatment, larvae are released systemically and severe inflammation can result (hypersensitivity reaction)

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Dracunulus (Guinea worm)

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Treatment of guinea worm (Dracunulus)

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Slow extraction of worm over several weeks; surgery; bendazole

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This disease remains a major problem in Sudan

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Guinea worm (Dracunulus)

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Clinical signs and symptoms of guinea worm (Dracunulus)

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Painful lesion, frequently with secondary bacterial infection

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Complications of guinea worm

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Hypersensitivity reaction in response to systemic release of larvae when worm is broken

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Prevention of guinea worm

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Separate drinking water from bathing/washing/wading water supplies. Filter drinking water. Larvicide treatment of water.

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WHO hopes to eradicate this disease in the near future

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Guinea worm (Dracunulus)

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Definitive host of filariases

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Humans

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Humans harbor both the adult worms and their newborn larvae of this class of roundworm

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Filariasis

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Life cycle of filarial roundworms

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Insect bite -> injection of mature larvae -> maturation and mating of adult worms -> female releases live first-stage larvae (MICROFILARIAE) -> mirofiliariae circulate in blood or migrate to tissue

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Intermediate host of filarial roundworms

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Blood-sucking insects

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Diagnostic stage of filarial roundworms

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Microfiliariae in blood or tissue

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Where do filarial roundworms mature?

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Thoracic muscles of infected insect

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This worm causes elaphantiasis

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Wuchereria bancrofti

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This disease is caused by adult worms in the lymphatics

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Elephantiasis (caused by Wuchereria)

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Intermediate host of Wuchereria

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Mosquito

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T/F: Wuchereria microfiliariae are pathogenic

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False. The adult worm, not the microfiliariae cause disease

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Microfiliariae are hard to detect in chronic forms of this disease because there are not many of them

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Elephantiasis (caused by Wuchereria)

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Treatment of elephantiasis

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Ivermectin

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This disease could possibly be eradicated over the course of 5 years with universal chemotherapy

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Elephantiasis (caused by Wuchereria)

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Tropical pulmonary eosinophilia is a complication of infection by this worm

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Wuchereria bancrofti (cause of elephantiasis)

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T/F: Tropical pulmonary eosinophilia is a common, fatal complication of Wuchereria infection

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False. It is a rare (0.5%) but fatal complication

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This worm can cause pulmonary infiltrates

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Wuchereria bancrofti (cause of elephantiasis)

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T/F: Tropical pulmonary eosinophilia is solely caused by Wuchereria bancrofti.

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False. Many types of worms can cause it, but Wuchereria is a common cause of this rare syndrome

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Diagnostic stage of Wuchereria

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Microfiliariae in blood

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Diagnostic stage of Onchocerca (River Blindness)

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Microfiliariae in tissue (skin)

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Geographic distribution of Wuchereria

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All tropical regions

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Microfilariae of this worm are harmless, but microfilariae of this worm cause disease

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Wuchereria microfiliariae are harmless (the adult form causes disease when it enters the lymphatics), but Onchocerca microfiliariae cause blindness

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Intermediate host of Onchocerca (River Blindness)

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Black fly (genus Simulium)

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This is where to find adult Onchocerca in infected humans

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Subcutaneous nodule at the site of the infecting black fly bite

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Clinical signs and symptoms of Onchocerca

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Dermatitis with severe itching, eye lesions, eosinophilia, subcutaneous nodules

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Microfilariae of this worm cause dermatitis with severe itching

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Onchocerca (River Blindness)

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Pathogenesis of blindness caused by Onchocerca (River blindness)

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Cornea: chronic keratitis and fibrosis
Iris: atrophy
Retina: chorioretinitis

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T/F: There is an autoimmune mechanism involved in River Blindness

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True.

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Geographic distribution of Onchocerca

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Focal areas of tropical Africa, Central and South America

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Diagnosis of this disease requires microfiliariae on a skin snip or adult worms in biopsy of nodule

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Onchocerca (River Blindness)

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Treatment of River Blindness (Onchocerca)

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Ivermectin (once a year; it kills microfiliariae before they can do harm)

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T/F: Ivermectin kills the adult and microfiliariael forms of Onchocerca

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False. It is only effective against the microfiliariae.

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This is the least serious of filiarial infections

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Loa Loa

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This worm causes symptoms due to migration of the adult worm through subcutaneous tissue

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Loa Loa (Eye Worm)

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T/F: Conjunctival migration is a common finding in Loa Loa (Eye worm)

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False. Only 15% of travelers with Loa Loa present with conjunctival migration; most present with Calabar swellings

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Chrysops is the intermediate host of this worm

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Loa Loa (Eye Worm)

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Intermediate host of Loa Loa

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Chrysops fly

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How long does it take for microfiliariae of Loa loa to mature in its host?

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2 weeks

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Diagnostic stage of Loa loa

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Microfiliariae in blood

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Infective stage of filariasis

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Infective larvae transmitted from the blood-sucking fly to the human

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How long does it take for Loa loa to mature once it has entered its human host

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1 year

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Survival time of Loa loa

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Several years (10-20)

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Calabar Swellings

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Itchy, chicken egg-sized edematous lesion seen in Loa loa infections. A hypersensitivity mechanism caused by migration of adults (5 cm)

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Geographic distribution of Loa loa

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Tropical Africa only

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Treatment of Loa loa

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Surgical removal, chemotherapy (DO NOT USE IVERMECTIN)

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Prevention of filiarial diseases

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Avoidance of fly bites

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What are the species, diseases they cause, their vectors, and the cause of pathology in the three filarial infections?

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Wuchereria - Elephan - Mosquito - Adults in lymphatics
Ochocerca - River Blind - Simulium (black fly) - Microfiliariae in tissues
Loa loa - Chrysops fly - Adults in tissues

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Clinical signs and symptoms of Loa loa

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Calabar swelling, adult migrating in conjunctiva