NEMATOEDES ----Enterobius vermicularis and Filarial parasites Characteristics of Nematodes (Adult) Enterobius vermicularis Wuchereria bancrofti and Brugia malayi

Characteristics of Nematodes Cylindrical and unsegmented Dioecious (male and female) Complete digestive tract (mouth / esophagus / intestine / anus) Direct life-cycle and soil-transmission (most) e.g. Ascaris / hookworm / Enterobius Indirect life-cycle and food or arthropods-transmission (small) e.g. Filaria / Trichinella

Enterobius vermicularis Consmopolitan, 30%~50% of the population, more prevalent in children than adults. Most common where people live under crowded conditions (orphanages / large families / kindergartens / primary school).

Morphology I Adult Female: White. 8~13 mm in size. Fusiform body with a long, thin, tapering tail. Alae (cuticular extension of head). Prominent bulb (esophagus posterior). Male: Like female, but about 1/3 to ½ size of female. The tail is curved. Rarely seen. (Why?)

Morphology II Egg Oval, clear and colorless. 50 to 60 µm in length. Flattened on one side. Contains a larva.

Life cycle

The types of infection Infection from environment Autoinfection: Female crawl out of anus and release eggs on the perianal region. Patients feel anus pruritus. Scratching leads to contamination of hands and nails. Then by hand-mouth result in reinfection. Retroinfection: Some eggs hatch on the perianal skin and become larvae. They will crawlback into the anus and mature into adults.

Characteristic of life cycle Human is the only host (direct life-cycle). The location of adult: Cecum and colon. Infective stage: Infective eggs. The female release eggs on the perianal skin at night. The types of infection: Autoinfection/retroinfection/infection

Clinical features Enterobiasis is frequently asymptomatic. The most typical symptom is perianal pruritus, especially at night, which may lead to excoriations and bacterial superinfection.  Occasionally, invasion of the female genital tract with vulvovaginitis and pelvic or peritoneal granulomas can occur.  Other symptoms : anorexia, irritability, and abdominal pain.

Laboratory Diagnosis Microscopic identification of eggs collected in the perianal area is the method of choice by cellophane tape method for diagnosing enterobiasis.  This must be done in the morning, before defecation and washing, Alternatively, anal swabs can also be used. Detection of adult on anal skin. 

Treatment and prevention Pyrantel pamoate / Albendazole / Melbendazole. Repeated treatment Laudering of bedding. Pay attention to personal hygiene and eating habits

Filarial parasites Filariasis(widely spread diseases) Filarial parasites Inhabit the lymphatic/subcutaneous tissue/peritoneal or throascic cavity Mansonella ozzardi; Loa loa; Dipetalonema perstans; D.streplocerca; Onchocerca volvulus; Brugia malayi; B. timori; Wucheria bancrofti

Wuchereria bancrofti and Brugia malayi

Morphology I Adult: White and thread-like. Two rings of small papillae on the head. Female:5~10cm in length Male: 2.5~4cm and a curved tail with two copulatory spicules.

Morphology II Microfilaria: 177~296 µm in length, a sheath with free endings. Bluntly rounded anteriorly and tapers to a point posteriorly. A nerve ring with no nuclei at anterior 1/5 of the body. Wuchereria bancrofti Brugia malayi

The morphological differences between two microfilaria W.bancrofti B. malayi Size 244~296 µm 177~230 µm Cephalic space Shorter Longer Nuclei Equal sized Unequal sized clearly coalescing countable uncountable Terminal nucleus No Two

Life cycle

Nocturnal periodicity ------Phenomen which the number of microfilariae in peripherial blood is very low density during daytime, but increase from evening to midnight and reach the greatest density at 10p.m to 2 a.m. May be related to cerebral activity and vasoactivity of pulmonary vessels.

Characteristic of life cycle Host: Mosqutoes (intermediate host) Human (final host) Location: Lymphatics and lymph nodes Infective stage: Inective larvae Transmission stage: Microfilariae Diagnostic stage: Microfilariae

Clinical Features Lymphatic filariasis often consists of asymptomatic microfilaremia.  Some patients develop lymphatic dysfunction causing lymphedema and elephantiasis(in limb or scrotum). Episodes of febrile lymphangitis and lymphadenitis may occur.  Pulmonary tropical eosinophilia syndrome, with nocturnal cough and wheezing, fever, and eosinophilia. 

Laboratory Diagnosis Microscopic examination is the most diagnostic procedure. Fresh blood smear Thick smear, stained with Giemsa. Concentration techniques include centrifugation of the blood sample lyzed in 2% formalin or filtration through a Nucleopore® membrane. Immunological tests

Treatment and prevention Diethylcarbamazine (DEC) for patients and carriers. Mass treatment in endemic areas with DEC. DEC added to table salt (1:3000) for six months. Elimination of mosquitoes. Protection of people from mosquitoes biting.

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