FILARIASIS

 Filariasis is a general term for an infection caused by subcutaneous nematodes (roundworms) of the genera Wuchereria and Brugia, found in the tropical and subtropical regions of the world. The disease is characterized by acute lymphatic inflammation or chronic lymphatic obstruction associated with intermittent fevers or recurrent episodes of dyspnea and bronchospasm.

PREDOMINANT SEX: Male

PREDOMINANT AGE: For both males and females, risk is greatest between the ages of 15 and 35 years.

PHYSICAL FINDINGS & CLINICAL 

PRESENTATION

• Clinical manifestations result from acute lymphatic inflammation or chronic lymphatic obstruction.

• Many patients are asymptomatic despite the presence of microfilaremia.

• Episodes of lymphangitis and lymphadenitis are associated with fever, headache, and back pain with painful swellings, and they are usually caused by the death of an adult worm.

• Acute funiculitis and epididymitis or orchitis may also be present; all usually resolve within days to weeks but tend to recur.

• Chronic infections may be associated with lymphedema, most commonly manifested by hydrocele.

• It is a progressive disease, leading to non-pitting edema and brawny changes that may involve a whole limb.

• Elephantiasis occurs in about 10% of patients, with skin of the scrotum or leg becoming. thickened and fissured; the patient is thereafter plagued by recurrent ulceration and infection.

• Chyluria, a condition that develops when lymphatic vessels rupture into the urinary tract, or chylocele may occur.

• Tropical pulmonary eosinophilia can also occur; it is caused by high IgE and results in nocturnal asthma, fatigue, and weight loss with pulmonary infiltrates on imaging and eosinophilia.

Fundamentals of Nursing 9th Edition Potter and Perry 

ETIOLOGY/CAUSES OF FILARIASIS 

Caused by one of three types of nematode 

parasite transmitted to humans by mosquitoes.

• W. bancrofti (>90% of cases; Fig. E1): Africa (including Egypt), areas of Central and South America, the Pacific Islands, and the Caribbean Basin.

• B. malayi: restricted to India, Malaysia, and other parts of Southeast Asia.

• B. timori: confined to the Indonesian archipelago. 

After bite of an infected mosquito:

• Filarial larvae move into lymphatic vessels and nodes and mature into adult male (2-4 cm) and female (4-10 cm) worms. Wolbachia bacteria are needed for filarial development.

• After fertilization, the female nematode produces 10,000 or more microfilariae that enter into the bloodstream via the lymphatics.

• Nocturnal periodicity, characteristic of B. malayi, is an increased presence of microfilariae in the circulation during the night.

• Microfilariae of W. bancrofti are maximal during late afternoon.

• Humans are the definitive hosts. Acute and chronic inflammatory and granulomatous changes in the lymphatic channels:

• Result from complex interaction of adult worms and host’s immune systems.

• Eventually lead to fibrosis and obstruction

• Most likely to develop into obstructive lymphatic disease with recurrent exposure over many years, with approximately 30% of those infected going on to develop lymphedema/hydrocele.

DIAGNOSIS OF FILARIASIS

DIFFERENTIAL DIAGNOSIS

Milroy’s disease, postoperative scarring, and lymphedema of malignancy.

Deep Vein Thrombosis: Signs, Treatment and Complications 

WORKUP

Diagnosis is suspected in individuals who have resided in endemic areas for at least 3 to 6 months or more and complain of recurrent episodes of lymphangitis, lymphadenitis, scrotal edema, or thrombophlebitis, with or without fever.

LABORATORY TESTS OF FILARIASIS

• Demonstration of microfilariae on a blood smear via Giemsa or Wright Stain for definitive diagnosis

• For patients from southeastern Asia: blood sample drawn at night, especially between 10 pm and 2 am

• Occasionally, microfilaremia in chylous urine or hydrocele fluid

• Prominent eosinophilia only during periods of acute lymphangitis or lymphadenitis

• Serologic tests for antibody, including enzyme-linked immunosorbent assay and indirect fluorescent antibody (often unable to distinguish among the various forms of filariasis or between acute and remote infection)

• Immunoassays (e.g., circulating filaria antigen [CFA]) only available for W. bancrofti: more successful in antigen detection in patients who are microfilaremic than in those who are amicrofilaremic

IMAGING STUDIES

• Chest radiography: reticular nodular infiltrates (tropical pulmonary eosinophilia syndrome).

• In men proven to be microfilaremic, scrotal ultrasonography to aid in the detection of adult worms and “filarial dance sign” may be seen.

 TREATMENT OF FILARIASIS

NONPHARMACOLOGIC THERAPY

• Standard of care for elephantiasis:

  1. Elevation of the affected limb

  2. Use of elastic stockings

  3. Local foot care

• General wound care for chronic ulcers and prevention of secondary infection

ACUTE GENERAL Rx OF FILARIASIS

• Diethylcarbamazine citrate (DEC) to reduce microfilaremia by 90%.

 1. Effect on adult worms, especially those of the Wuchereria species, less certain.

 2. Given in an oral dose of 6 mg/kg PO qd in 3 divided doses × 14 days or 6 mg/kg/day as single PO dose daily × 14 days plus doxycycline 200 mg/day × 6 weeks (to decrease number of Wolbachia and number of microfilaria).

 3. DEC should not be used if coinfection with Loa loa or onchocerciasis is suspected, because of severe adverse reactions, including blindness and death.

• Ivermectin alone or in combination with DEC to decrease microfilaremia. Ivermectin kills the microfilariae but does not kill adult worms.

• Side effects of these drugs include severe hypotensive reactions with dizziness, headache, fever, and vomiting, especially in patients with high microfilarial loads.

• World Health Organization (WHO) recommendation: DEC given as a single dose, alone or (preferably) in combination with ivermectin as treatment in endemic areas.

• Antibacterial agents (a penicillin or cephalosporin) may be indicated to treat coexisting bacterial soft tissue infection (cellulitis or lymphangitis), which frequently complicates filariasis of the lower extremities.

• Doxycycline for 1 to 2 months may decrease the number of adult worms and improve lymphatic pathology.

Aortic Valvular Stenosis: Causes, Risk Factors, Diagnosis, Treatment

CHRONIC Rx OF FILARIASIS

• Surgical drainage of hydroceles

• No satisfactory therapy for patients with chyluria.

PREVENTION OF FILARIASIS

Individuals who intend to travel or reside in endemic areas should be advised to institute preventive measures such as the use of netting and insect repellents containing DEET, especially at night when mosquitos transmitting disease are most active.