• Brugia malayi is a filarial worm belongs to phylum nematoda which is one of three causative agents of elephantiasis (lymphatic filariasis) in humans. ( other are- Wuchereria bancrofti, Brugia timori)
• Brug in 1927 describe for the first time about new type of microfilaria in blood of natives in Sumatra. From where the genus acquired its name, Brugia.
• The adult B.malayi worm of was described by Rao and Maplestone in India (1940).
• B. malayi has a more restricted distributions than other filarial worms and is commonly found in open swamps and the rice growing areas of coastal regions.
• It is endemic in India, Srilanka, Philippines, Southern Thailand, North Veitnam, China, South Korea and Japan.
• Besides B. malayi, the genus also includes B. timori, which is human parasite causing lymphatic filariasis.
• Other animal species such as B. pahangi and B. patei infecting dogs and cats.
• Human are the primary host.
• Leaf monkeys are also definitive hosts and reservoir of sub periodic B. malayi. Hence, zoonotic infection can occur from infected monkeys to humans.
• Mosquitoes are the intermediate host.

Habitat

• The adult worm B. malayi is found in the lymphatic system of man and other mammals.
• Microfilaria are mainly found in the peripheral blood circulation.

Morphology of Brugia malayi:

Adult worm:

• The adult worm is similar to Wuchereria bancrofti but are smaller in size.
• The worm resembles a delicate white thread.
• The mature females vary in length from 4.3 – 5.5 cm and in breadth from 0.13-0.17 mm.
• Mature males measure 1.2-2.3 cm in length and 0.07- 0.08 mm in breadth.

Microfilaria

• Microfilaria are colorless and transparent with blunt heads and pointed tails in unstained preparations.
• They lie folded with head close to tail.
• Each microfilaria measures 177-230 µm in length and 5-6 µm in diameter. They possess secondary kinks, instead of smooth curves. The presence of two distinct nuclei at the tip of the tail is the distinguishing feature of microfilaria.
• The nuclei is present at the extreme tip of the tail and other midway between the tip and the posterior column nuclei.

Third stage larvae: an Infective form

• L3 larva is the infective form of parasite are found in the mosquito vector.
• They are elongated, filariform and measure 1500 µm to 1800 µm in length and 18-23 µm in breadth.

Periodicity of Brugia malayi:

• B. malayi generally shows nocturnal periodicity. However, two variants of Brugia malayi are recognized.

1. Nocturnal periodic Brugia malayi

• It is the most prevalent form of parasite
• Microfilaria show nocturnal periodicity
• Transmission occurs mainly by Anopheles and Mansonia mosquito

2. Sub periodic Brugia malayi

• It is less common form
• Microfilaria are found in the day time
• Transmission occurs by Mansonia and Coquillettidia mosquitoes

Pathogenesis of Brugia malayi

• Humans are the definitive host and mosquitoes are the intermediate hosts of Brugia spp. Infected human are the main sources and reservoir of infection. Man to Man transmission occurs by the bite of Anapheles and Mansonia.
• The life cycle of filarial parasites involves four larval stages and an adult stage.
• Infection begins with the bite of infected mosquito on the skin and deposition of infective stage larvae (L3).
• The larvae then pass through the puncture wound and reach the lymphatic system.
• Within the lymphatics and lymph nodes, the L3 larvae undergo molting and development to form L4 larvae.
• This takes about 7-10 days for both B. malayi and W. bancrofti
• The L4 larvae undergo a subsequent molting/developmental step to form adult worms. This occurs about 4-6 weeks after L3 entry in the case of B. malayi.
• The adult worms take permanent residence in afferent lymphatics or the cortical sinuses of lymph nodes and generate microscopic live progeny called “microfilariae”.
• The female worms can give birth to as many as 50,000 microfilariae per day, which find their way into the blood circulation from the lymphatics.
• The adult worms are estimated to survive for a period of 5-10 years although longer durations have been recorded.
• The microfilariae of B. malayi, for the large part, exhibit a phenomenon called nocturnal periodicity, i.e., they appear in larger numbers in the peripheral circulation at night and retreat during the day.
• Subperiodic or nonperiodic of B. malayi are also found in certain parts of the world.

I. Pathology of acute filariasis

Lymphadenitis:

• It is the typical feature. The more classical is acute filarial adenolymphangitis, which is felt to reflect an immune-mediated inflammatory response to dead or dying adult worms.
• The attacks of lymphadenitis occur at regular intervals and often are precipitated by hard muscular exercise.
• The episodes of attacks vary from 1-2 attacks per year.
• Lymphadenitis typically occurs in the inguinal region.
• Occasionally the auxillary lymph nodes are also involved.
• It occurs infrequently at atypical sites such as the popliteal lymph nodes or breasts.

Lymphangitis

• Lymphadenitis is followed by Retrograde lymphangitis

Lymphatic abscess

• The infected lymph nodes may suppurate and form abscess.
• These are usually superficial.
• They rupture leaving behind ulcers.

II. Pathology of chronic filariasis

• The common sites of elephantiasis include, the leg below the knee and less frequently the arm below the elbow.
• Genital involvement and chyluria characteristically are absent.

Clinical manifestation of lymphatic filariasis:

• Incubation period is short and varies from 6-16 month.
• B. malayi shows following clinical stages.

i. Endemic normal and asymptomatic stage:

• Most infection are asymptomatic and common among infected persons in endemic areas with no symptoms of filarial infection and yet, on routine blood examinations, demonstrate the presence of significant numbers of parasites.

ii. Acute filariasis:

• It is characterized by recurrent attacks of lymphadenitis (inflammation of lymph nodes) and lymphangitis associated with fever, chill and other constitutional symptoms.
• The attacks are followed by a characteristics retrograde lymphangitis. The affected lymph vessels become cord-like and tender. The frequency of attacks per year to several attacks per month.
• The infected lymph nodes may suppurate and form abscesses.
• The lymph node abscess is the characteristics of Malayan filariasis.
• Incomplete resolution of the oedema after each attacks leads to the characteristics chronic stage.

Chronic filariasis:

• It is characterized by elephantiasis that develops after 10-15 years in a small number infected population.
• The legs below the knee, less frequently the arms below the elbow are characteristically affected.
• Genital involvement and chyluna are not reported in Malayan filariasis, this occurs only along with bancroftian filariasis.

Lab Diagnosis

• Same as lab diagnosis of W. bancrofti

Treatment of Brugia malayi

• Diethylcarbamagine (DEC): is relatively effective in smaller dose.
• Dose regimen consists of 50 mg on first day; 50 mg three times daily on 2^nd day; 100 mg three times daily on 3^rd day and finally 2 mg/kg/day in three divided doses from 4^th day till 21^st day.

Brugia malayi: Introduction, Morphology, Pathogenesis, Clinical manifestation and Treatment

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• Loa loa is a blood dwelling nematode that is parasitic in humans. The adult worm wanders through the subcutaneous tissue but is most obvious as it crosses the conjunctiva of the eye, hence leading to its common name, the African eye worm. It causes loa loa filariasis (loiasis). It is one of three parasitic filarial nematode that causes subcutaneous filariasis in humans.

Habitat

• The adult worm inhibits the subcutaneous tissue of man, often in the sub conjuctival tissue of the eye. The microfilariae are found in blood.

Morphology

Adult worm

• The adult worm are thin, whitish and thread like.
• The anterior and tapers to a narrow head. Surface of the body is covered with small knobs.
• Microscopically the cuticula is found to have numerous rounded protuberances (cuticular bosses) which vary in number and arrangement in two sexes.
• The female worm is 4-7 cm in length and 0.5mm in diameter.
• The life span of worm is 4-12 years.

Microfilaria

• They are found in peripheral blood during day time. Occasionally microfilaria have been demonstrated in the urine, sputum and even CSF.
• Microfilaria is sheathed and measures 250-300 mm in length and 6-8 mm in breadth.
• The column of nuclei extends upto the tail-tip.
• Sheath stains poorly with Geimsa stain but stains well with iron-haematoxylin.

Life cycle of loa loa:

• Loa loa completes its life cycle in two hosts:
• Definitive host: Human

• Man acquires infection by the bite of infected female chrysops. During infection larva enter in large numbers through the punctured wound on the skin made by the fly, during the blood meal.
• The larva enter the subcutaneous tissue and mount to develop into adult worms within a period of 6-12 months.
• Adult worm occasionally migrate in the sub conjunctival tissue.
• The female worm after fertilize by males produce microfilarial larva that circulate in the peripheral blood during the day time and also found in the sub-cutaneous tissue.
• When a female chrysops bites the infected human to suck the blood, microfilaria is ingested that enter the fly’s stomach.
• Microfilarial larvae lose their sheath, penetrate the wall of the stomach and invade thoracic muscles where they undergo changes to form the infective L3 larva.
• Development in fly is completed in about 10 days.
• The mature infective larva than migrate to the mouth parts of chrysops. When this fly bites a new hosts for blood meal, the cycle is again repeated.

Mode of transmission of loa loa:

• Infected man is the only source and reservoir of infection for loa loa.
• Transmission is acquired by the bite of female chrysops species

Pathogenesis and pathology of loa loa:

• Microfilaria are not pathogenic.
• Adult loa loa worms which live in the subcutaneous tissue are pathogenic.
• The migrating adult worms provoke an intense inflammatory reaction.
• Calabar swelling is the typical pathological feature of the loa loa filariasis. It is formed as a result of an allergic response to adult worms migrating in the subcutaneous tissue.

Clinical manifestation of loa loa filariasis:

• Loa loa filariasis (loasis) is the disease produced by adult worm in human.
•  The incubation period is on an average 3-4 years.
• Loiasis is  asymptomatics in many pcases.

Symptomatic manifestation of loa loa filariasis:

Skin lesions

• Skin lesions consists of colabar swelling or fugitive swelling.
• During migration of the adult worm, it causes oedema of subcutaneous tissues, known as calebur swelling. They disappear in course of 2-3 days and are regarded as allergic reaction of the tissues to filarial toxins.
• Localized pain and itching for several hours usually precede the onset of the swelling. Usually one swelling develops at a time. The swelling is non erythematous, measures 3-10 cm in diameter and last for few days to weeks. The wrist joints or knee joints are most frequently affected. Worms are not usually present in the swellings but are present below surface of the skin.

Ocular lesions

• These consists of;
• Conjunctival granuloma: It is caused by the migration of adult worms in the sub-conjunctival tissues. These granulomas are present as solitary or multiple small nodules measuring 2mm in diameter. These are found in the deeper layers of conjunctiva close to the sclera tissue.
• Oedema of the eyelid: It is painless condition frequently accompanied by itching but not fever or any other constitutional symptoms.
• Proptosis: This condition is known as ‘bug eye’ or ‘bulge eye’ caused by the edema of the orbital cellular tissue. It is a painless condition and of rapid onset frequently associated with itching.

Complications of loasis:

• These include frequent recurrence of fugitive swellings, endomyocardial fibrosis, retinopathy, encephalopathy, neuropathy and arthritis.
• Loa loa meingoencephalopathy is a severe and often fatal complications of infection.

Epidemiology and geographical distribution of loa loa:

• Loiasis is endemic across central Africa. This is widely prevalent in rain forest of both west and central Africa, extending from Sierra leone to Uganda and south ward to Angol. High rate of infection are found in Nigeria, Cameroon and Zaire.

Diagnosis of loa loa:

• Clinical diagnosis is suggested in patients with typical fugitive swellings, high eosinophilia and history of residence in an area endemic for the disease
• Specific diagnosis is made by demonstration and identification of microfilaria in the peripheral blood
• Demonstration of the worm in the cornea or over the bridge of the nose.
• Identification of the adult worm surgically removed from the skin or conjunctiva.

Treatment of loa loa:

• Diethylcarbamazine(DEC) is the drug of choice.
• Dose – 6mg/day, 3 times daily for 12 days

Prevention and control of loa loa:

• Treatment of infected populations
• Using insect repellent
• Wearing protective clothing
• Avoiding visit to the places endemic for the disease

Loa loa: Habitat, morphology, life cycle, pathogenesis, clinical manifestation, epidemiology, diagnosis, treatment, prevent and control

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