What is the infectious organism responsible for elephantiasis?

Infectious Organism Responsible for Elephantiasis

Elephantiasis is primarily caused by the filarial nematodes Wuchereria bancrofti, Brugia malayi, and Brugia timori, with W. bancrofti accounting for approximately 90% of all cases of lymphatic filariasis worldwide. 1, 2, 3

Causative Organisms and Distribution

Primary Pathogens

• Wuchereria bancrofti: The most common cause (90% of cases), found in:

  • Africa
  • West Pacific regions
  • Caribbean
  • Sporadic cases in South America, India, and Southeast Asia 1

• Brugia malayi: Primarily found in Southeast Asia 1

• Brugia timori: Mainly found in Southeast Asia, particularly in Indonesia 1, 2

Transmission

These parasites are transmitted through the bite of infected mosquitoes, including:

• Aedes species
• Anopheles species
• Culex species 1

Pathophysiology and Disease Development

1. Infection Cycle:

   • Mosquitoes deposit infective larvae on the skin during blood meals
   • Larvae migrate to lymphatic vessels and lymph nodes
   • Mature into adult worms in lymphatic system
   • Adult worms produce microfilariae that circulate in the bloodstream (typically at night)

2. Disease Progression:

   • Initial infection is often asymptomatic but causes lymphatic damage
   • Acute phase: fever, lymphadenitis, and lymphangitis
   • Chronic phase: lymphoedema and elephantiasis (severe swelling of limbs or genitals) 1

3. Incubation Period:

   • W. bancrofti: 7-8 months until microfilariae appear
   • B. malayi: 2 months until microfilariae appear
   • Clinical symptoms: Variable, 4 weeks to 16 months 1

Clinical Presentation

• Early stages: Often asymptomatic despite ongoing lymphatic damage
• Acute manifestations: Fever and localized skin inflammation with lymphadenitis and lymphangitis
• Chronic manifestations: Progressive lymphoedema (elephantiasis) and scrotal oedema/hydrocele
• Non-immune travelers: May present with tropical pulmonary eosinophilia (fever and respiratory symptoms) 1

Diagnostic Approach

1. Serological testing: To detect filarial antigens
2. Nocturnal blood microscopy: Collected between 10 pm and 2 am (4 citrated blood bottles, 20 ml total volume, not refrigerated) to detect microfilariae 1

Important Distinction

It's worth noting that not all cases of elephantiasis are caused by filarial infections. Non-filarial endemic elephantiasis (podoconiosis) can occur in areas where filariasis is not endemic, typically associated with barefoot exposure to certain soil types 4.

Treatment

Treatment requires specialist input and includes:

1. First-line therapy: Diethylcarbamazine (DEC) 6 mg/kg in 3 divided doses for 14 days plus doxycycline 200 mg daily for 6 weeks 1

2. For high microfilarial loads (>1000 mf/ml):

   • Screen for strongyloidiasis
   • Treat with prednisolone and albendazole 200 mg twice daily for 21 days
   • After achieving <1000 mf/ml, proceed with DEC with prednisolone cover 1

3. Alternative approach targeting symbiotic Wolbachia bacteria:

   • Doxycycline 200 mg once daily for 6 weeks
   • Combined with ivermectin 200 μg/kg monthly for 3 months 1, 5

Prevention and Control

The WHO's mass drug administration (MDA) strategy using diethylcarbamazine, albendazole, and ivermectin has been partially successful in controlling lymphatic filariasis globally 2.

Caution

Special care must be taken in areas co-endemic with other filarial infections like onchocerciasis or loiasis, as treatment approaches may need modification to prevent adverse reactions 1.