Filariasis

Filariasis is most commonly caused by the filarial worm, Wucheria bancrofti. It is transmitted by mosquitoes. Initial symptoms are episodes of fever, lymphadenitis, lymphangitis, and swelling of the leg, arm, or male genitalia. Chronic lymphedema can cause hydrocele, orchitis, and elephantiasis.

CASES/YEAR
0 (US); 120,000 (Global)
CATEGORY
AGENT TYPE
Helminths
OTHER NAMES
Wucheria bancrofti filariasis; Brugia malayi filariasis; Brugia timori filariasis;
ACUITY
Acute-Moderate
INCUBATION
Microfilariae appear in blood: 3-6 months (B. malayi); 6-12 months (W. bancrofti); [CCDM]
INITIAL SYMPTOMS
Episodes of fever, lymphadenitis, lymphangitis, and swelling of the leg, arm, or male genitalia; Episodes last 3-7 days beginning in adolescence or early adulthood; Chronic lymphedema can cause hydrocele, orchitis, and elephantiasis; [PPID, p. 3447]
PRECAUTIONS
"Not directly transmitted from person to person. . . . A large number of infected mosquito bites are required to initiate infection in the host." [CCDM, p. 213]
COMMENTS
FINDINGS:
The body's reaction to the adult filarial worm in the lymphatic vessels leads to chronic inflammation, lymphatic obstruction, and secondary bacterial infections. Lymphatic filariasis may cause epididymitis, hematuria, proteinuria, and arthritis. [Merck Manual, p. 1673] Some of the different syndromes are: 1) asymptomatic and negative for parasites; 2) asymptomatic and microfilariae present; 3) acute recurrent lymphadenitis and retrograde lymphangitis; 4) lymphostasis (hydrocele, chyluria, and elephantiasis); 5) tropical pulmonary eosinophilic syndrome (nocturnal asthma, interstitial lung disease, recurrent fever, and no microfilariae in the blood). [CCDM, p. 211] Verrucous skin lesions and lymphorrhea are common in chronic cases. [Guerrant, p. 731-2] "Most infections are asymptomatic, but lymphatic dysfunction may lead to lymphedema of the leg, scrotum, penis, arm, or breast years after infection." [CDC Travel, p. 211] Extended travelers (3 to 6 months) can develop acute lymphatic inflammation with or without urticaria. [Harrison ID, p. 1139]

ADENOLYMPHANGITIS:
Patients with acute adenolymphangitis present with sudden onset of fever and painful, swollen lymph nodes. The lymphangitis is retrograde, moving away from the lymph nodes. Typically, patients have one-week episodes of fever and lymphadenitis several times a year. Dermatolymphangioadenitis is an acute disease variant with high fever, myalgias, headache, and inflammatory skin lesions (vesicles, ulcers, and hyperpigmentation) often diagnosed as cellulitis. [Guerrant, p. 731-2]

TPE:
Tropical pulmonary eosinophilia (TPE) is uncommon. TPE is the pulmonary reaction to microfilariae in the capillaries and may progress to pulmonary fibrosis. Patients with TPE have marked eosinophilia, low-grade fever, and episodes of wheezing. [Merck Manual, p. 1673] In TPE, W. bancrofti and B. malayi infections cause fever, splenomegaly, lung infiltrates, and eosinophilia. In TPE, no microfilariae are present. [Cohen, p. 1777] Patients with TPE have coughing and wheezing, especially at night, and may have infiltrates, cavitation, and eosinophilic pleural effusion. Other symptoms of TPE are weight loss, eosinophilia, fever, and adenopathy. [Guerrant, p. 945]

EPIDEMIOLOGY:
Humans are reservoirs. Cats, civets, and primates are reservoirs of limited significance in Malaysia, southern Thailand, the Philippines, Timor-Leste, and Indonesia. [CCDM, p. 212] TPE is an uncommon complication with most cases reported in India, Pakistan, Sri Lanka, Brazil, Guyana, and Southeast Asia. The risk of lymphatic filariasis for the traveler is extremely small, given the inefficiency of transmission. [Guerrant, p. 733]
DIAGNOSTIC
Giemsa stain of blood smear or detect live worms under microscope; Concentrate microfilariae by filtration of anticoagulated blood; [CCDM] Serology (EIA & RAPID); RAPID & PCR available from NIH (301-496-5398); [Harrison ID, p. 1040t]
SCOPE
Long term travelers in "sub-Saharan Africa, Egypt, southern Asia, the western Pacific islands, the northeastern coast of Brazil, Guyana, Haiti, and the Dominican Republic." [CDC Travel, p. 211]
SIGNS & SYMPTOMS
  • >fatigue, weakness
  • >fever
  • >myalgia
  • H anemia
  • H eosinophilia
  • H lymphadenopathy
  • N headache
  • R cough
  • R wheezing
  • S lymphadenitis, acute
  • S lymphangitis
  • S papules or plaques
  • S skin blister or vesicles
  • S skin or subcutaneous nodule
  • S ulcer of skin
  • S urticaria
  • S warty growth of the skin
  • U hematuria
  • X cystic or cavitary lesions
  • X lung infiltrates
  • X pleural effusions
  • *arthritis
  • *epididymo-orchitis
  • *erythema nodosum
  • *glomerulonephritis
  • *weight loss
ANTIMICROBIC

Yes

VACCINE

No

ENTRY
VECTOR
Mosquitoes
RESERVOIR
Cats, Monkeys, Human, Wild Animals
RISK FACTORS
  • Travel to endemic area
REFERENCES FOR CASES/YEAR
1.
2. (Global) 120,000 currently infected and about 40 million disfigured and incapacitated; [Fact sheets from WHO 2013]