MLS 602: General and Medical Microbiology

Lecture: 11

Edwina Razak

edwina.razak@fnu.ac.fj

Tissue and Blood Dwelling Nematode

Learning Outcomes

• Describe the tissue nematodes of medical importance.

• Evaluate different characteristics of tissue nematodes.

• Explain and evaluate the different lifecycles of common intestinal nematodes of humans.

• Critically analyse the parasitology methods used to diagnose intestinal nematodes.

Introduction

• The Neglected Tropical Diseases (NTDs), which have suffered from a lack ofattention by the public health community, include parasitic diseases suchas lymphatic filariasis ,onchocerciasis, STHs and Guinea worm disease.

• The NTDs affect more than 1 billion people—one-sixth of the world’spopulation—largely in rural areas of low-income countries. These diseasesextract a large toll on endemic populations, including lost ability to attendschool or work, retardation of growth in children, impairment of cognitiveskills and development in young children, and the serious economicburden placed on entire countries.

Common Tissue Nematodes are:

• Trichinella spiralis-adults in small intestines and larvae in tissues (mainly in muscles).

• Toxocara canis- (dog roundworms) larvae in organs (liver, brain, eyes) causing visceral larva migrans.

• Dracunculus medinensis- (guinea worm) adult female in subcutaneous tissues.

• Filarial worms

Trichinella spiralis – trichinosis

• most commonly associated with

pork.

• Trichinella spiralis is a parasite

of carnivorous mammals.

• common in rats and in swine fed uncooked garbage and slaughterhouse scraps.

• result of consumption of raw or undercooked pork.

Morphology

• Adult female worm

measures 3-4 mm in length.

• adult male worm measures

1.4-2.6 mm in length.

• encysted larvae measure

800-1300 μm in length.

Life cycle:

• Infective stage larvae are ingested in meat products.

• Tissue is digested, larvae are freed in the intestine.

• They mature into adult males and females.

• Female in mucosa releases larvae. These disseminate throughout the body via the bloodstream.

• Larvae encyst in striated muscle

Life cycle:

Pathology and Clinical features

There are three clinical phases:1. The intestinal phase: lasting 1-7 days - asymptomatic; sometimes

cause nausea, vomiting, diarrhea, constipation, pain fever, muscle pain, bilateral periorbital edema, and increased eosinophil count.

2. Migrational phase - high fever, blurred vision, edema, cough and pleural pains.

3. The muscle phase: which causes myalgia, palpabral edema, eosinophilia, fever, myocarditis, meningitis, bronchopneumonia.

Laboratory Diagnosis

• Muscle Biopsy

• Detection of larvae in blood or CSF

• Detection of larvae and adult worms in stool (rare).

• ELISA- Enzyme Linked Immunosorbent Assay

Treatment: Thiabendazol

Dracunculus medinensis – The Guinea

Worm

• An important parasite in the Middle East, central India and Pakistan. Also found in Africa in the Sudan and scattered through central equatorial regions, and on its west coast.

• It is believed to have been the ‘fiery serpent’ in the Bible, which tormented the Israelites on the banks of the Red Sea. The technique of extracting the worm by twisting it on a stick, still practised by patients in endemic areas is said to have been devised by Moses.

• Sometimes classified with the filarial worms, but Dracunculus is not a true filaria.

Worm oozing out from the ruptured blister

Life Cycle

• Infective stage exists in a water flea (copepod – the intermediate host). • Humans become infected by drinking water containing the infected copepod. • Larvae penetrate the digestive tract to enter the deep connective tissues where

they mature in about 1 year. • Females migrate to the subcutaneous tissue (usually the skin of the extremities).• Females release larvae which leave the human through ruptured blisters on the

skin.• The larvae enter the water and are ingested by copepods.

Symptoms and Diagnosis

Major pathology and symptoms• Mild allergic symptoms such as

urticaria during the migration phase.

• A papule develops into a blister with localized erythrema and tenderness.

• Generalized symptoms include nausea, vomiting, diarrhea, and possibly asthma attacks.

• Additional complications include secondary bacterial infections, permanent damage to joints.

Diagnosis• Visual observation of skin blister.

The worm’s serpentine presence beneath skin can be seen.

• Induce release of larvae from the skin ulcer by applying cold water.

• Microscopy can identify the special features of the worm.

• An intradermal test with guinea worm antigen elicits positive response.

Filarial Worms

• The Filariae are long thread-like nematodes. Eight species inhabit portions of the human subcutaneous tissues and lymphatic system.

• Adults of all species are parasites of vertebrate hosts.• Female worms produce eggs. The eggs modify, becoming elongated and worm-

like in appearance and adapting to life within the vascular system. • Modified eggs, referred to as microfilariae, are capable of living a long time in

the vertebrate host, but cannot develop further until ingested by an intermediate host and vector, an insect.

• Microfilariae transform into infective larvae in the insect and are deposited in the next host when the insect takes a blood meal.

Wuchereria bancrofti

• Bancroft's Filariasis.” A blood & lymphatic dweller (Lymphatic filariasis) . The infection often results in elephantiasis.

• Vectors - Culex, Aedes, & Anopheles mosquitoes.

• Diagnosis - Detection and identification of microfilaria in stained blood smears. Exhibits a marked circadian migration, best seen at night after 10 P.M.

• Morphology - Microfilariae are sheathed, and the nuclear column does not extend to tip of tail.

General life cycle

• Human infection is acquired when infective larvae enter the skin at the arthropod’s feeding site.

• Larval migration and development takes place in tissue.

• Adults are in various tissues (according to species). They mature and produce microfilariae.

Symptoms

• Swelling, due to allergic reaction occurring around adult worms, produces obstruction & elephantiasis. Each individual reacts differently. Very few develop elephantiasis, but in some this is extensive

• Filariasis does not kill, but may cause great suffering, disfiguration and disability

• Associated with malaise, headache, nausea, vomiting and low grade fever Recurrent attacks of pruritus and urticariamay occur. Some develop ‘fugitive swellings’—raised, painless, tender, diffuse, red areas on the skin, commonly seen on the limbs.

• Accumulation of fluid occurs due to obstruction of lymph vessels of the spermatic cord and also by exudation from the inflamed testes and epididymis

Laboratory Diagnosis

• Demonstration of microfilaria in peripheral blood. Microfilaria may also be detected in other specimens such as chylous urine or hydrocoelefluid. Sometimes it can be seen in biopsy specimens.

• Microfilaria can be demonstrated in unstained as well as stained preparations.

• Leishman stain is used for thin smears

• A drop of blood on a slide with cover slip using EDTA specimen for immediate observation of worms.

Other Filarial Worms

Brugia malayi

• “Malayan filariasis.” A blood & lymphatic dweller. The infection can cause elephantiasis, but is not as disfiguring or common as with Wuchereria bancrofti.

• Vectors - Mansonia, Anopheles & Aedesmosquitoes.

• Diagnosis - Detection and identification of microfilaria in stained blood smears.

• Morphology - Microfilariae are sheathed, nuclear column extends to tip of tail with two nuclei near end of tail, one in a swelling just short of tail’s end, the other in the end of the tail.

Onchocerca volvulus

• The “blinding filaria.” Infections involve the dermis and subcutaneous tissues, where adults gather within nodules.

• Vector - Simulium flies (blackfly, or buffalo gnat).

• Diagnosis - microfilariae are found in skin scrapings from around nodules.

• Morphology - Microfilariae not sheathed; found only in skin, not in the blood stream.

• The specimen is best collected around midday.

Loaloa

• The “eyeworm.” Infections involve the dermis and subcutaneous tissues (Calabarswellings).

• Vector - Crysops (mango fly), a large fly with biting mouthparts.

• Diagnosis - Usually made from clinical symptoms, but if laboratory confirmation is required,circardian migration

• Infections cause a localized subcutaneous edema, particularly around the eye, because of larval migration and death in capillaries. Living adults cause no inflammation; dying adults induce granulomatous reactions.

• sheathed, nuclei extending to pointed tail tip

Loaloa

Mansonella- SEROUS CAVITY FILARIASIS

MANSONELLA OZZARDI

New World filaria seen only in Central and South America and the West Indies.

The adult worms are found in the peritoneal and pleural cavities of humans.

The non-periodic unsheathed microfilariae are found in the blood.

Culicoides species are the vectors. Infection does not cause any illness.

Diagnosis is made by demonstrating microfilariae in blood. No treatment is available.

MANSONELLA PERSTANS

• Distributed in tropical Africa and coastal South America.

• The adult worms live in the body cavities of humans, mainly in peritoneum, less often in pleura and rarely in pericardium.

• The microfilariae are unsheathed and subperiodic.

• Vectors are Culicoides species. African primates have been reported to act as reservoir hosts.

• Infection is generally asymptomatic, though it has been claimed that it causes transient abdominal pain, rashes and malaise.

• Diagnosis is by demonstration of the microfilariae in peripheral blood.

Features differentiating different species of Microfilariae

LARVA MIGRANS

There are three types of larva migrans:

• Cutaneous larva migrans (Creeping eruption)

1. Ancylostoma braziliens: infects both dogs and cats.

2. Ancylostoma caninum: infects only dogs.

• Visceral larva migrans

1. Toxocara canis (Dog ascarid)

2. Toxocara catis

Clinical features:

• Majority are asymptomatic.

• Eosinophilia

• Cerebral, myocardial and pulmonary involvement may cause death.

Diagnosis - Identification of larvae in tissue.

Treatment - Thiabendazole: 25 mg/kg twice daily for 5 days.

Questions??

1. Type of sample required Wucheria bancrofti identification.

2. Lymphatic filariasis symptoms.

3. Name the three clinical phases for Trichenella.