What do you mean by infectious and communicable diseases? Mention the causative agent and means of spread of filaria. Also describe the symptoms, diagnosis, treatment and preventive measures of filaria.

Infectious and Communicable Diseases

While often used interchangeably, "infectious diseases" and "communicable diseases" have distinct meanings, though all communicable diseases are infectious.

• Infectious Diseases: These are illnesses caused by pathogenic microorganisms such as bacteria, viruses, fungi, or parasites that multiply within a host. An infectious disease is any disease caused by germs that can spread from person to person, animal to person, or be present in the environment (air, water, food, soil). However, not all infectious diseases are necessarily communicable. For example, tetanus is an infectious disease caused by bacteria, but it is typically acquired through wounds contaminated with soil, rather than direct person-to-person transmission.
• Communicable Diseases: This is a subset of infectious diseases that can be transmitted directly or indirectly from one person to another, or from animals to humans. Transmission can occur through direct contact (e.g., touching, bodily fluids), airborne droplets, contaminated food or water, or via vectors like mosquitoes or ticks. Thus, a communicable disease is capable of spreading from one host to another.

Filaria: Causative Agent and Means of Spread

Filariasis, specifically Lymphatic Filariasis (LF), is a neglected tropical disease caused by thread-like parasitic roundworms and transmitted by mosquitoes.

Causative Agent:

• Parasitic Worms (Nematodes): The primary causative agents are three species of filarial worms:
  • Wuchereria bancrofti: Responsible for about 90% of lymphatic filariasis cases globally, and 99.4% in India.
  • Brugia malayi: Accounts for most of the remaining cases, and 0.6% in India.
  • Brugia timori: Causes a small percentage of cases, primarily in certain Southeast Asian islands.
• Vectors (Mosquitoes): These worms are transmitted to humans through the bites of infected mosquitoes. Different mosquito species serve as vectors depending on the geographical region:
  • Culex quinquefasciatus: The main vector in urban and semi-urban areas, particularly for Wuchereria bancrofti.
  • Anopheles spp.: Common vectors in rural areas.
  • Aedes spp.: Found in some island regions.
  • Mansonia spp.: Vectors for Brugia malayi and Brugia timori.

Means of Spread:

The transmission cycle involves humans and mosquitoes:

1. An infected person carries microscopic larvae called microfilariae in their bloodstream.
2. A mosquito bites the infected person and ingests these microfilariae.
3. Within the mosquito, the microfilariae mature into infective larvae.
4. When this infected mosquito bites another healthy person, it deposits the infective larvae onto the skin.
5. The larvae enter the body through the bite wound and migrate to the lymphatic system, where they mature into adult worms.
6. Adult worms can live for several years in the lymphatic vessels, producing millions of new microfilariae, thus continuing the cycle.

Symptoms, Diagnosis, Treatment, and Preventive Measures of Filaria

Symptoms:

Many infected individuals remain asymptomatic for years, yet the parasitic worms cause damage to the lymphatic system, kidneys, and immune system. Chronic symptoms develop over time:

• Acute Manifestations:
  • Fever, chills, and headache.
  • Acute lymphadenitis (swelling and pain in lymph nodes).
  • Acute filarial lymphangitis (inflammation of lymphatic vessels, often appearing as red, tender streaks on limbs).
  • Episodic funiculitis, epididymitis, and orchitis (inflammation of the spermatic cord, epididymis, and testes in males).
• Chronic Manifestations:
  • Lymphedema: Swelling and thickening of the skin and underlying tissues, most commonly affecting the limbs (arms and legs), but also possible in breasts and genitalia.
  • Elephantiasis: Severe, irreversible lymphedema characterized by gross enlargement and hardening of the skin, giving it an elephant-like appearance. This is a severe disfigurement.
  • Hydrocele: Swelling of the scrotum due to accumulation of fluid around the testes, a common chronic manifestation in men.
  • Chyluria: Milky-white urine due to the leakage of lymphatic fluid into the urinary tract.

Diagnosis:

Diagnosis typically involves detecting microfilariae or filarial antigens.

• Microscopic Examination of Blood Smears: The gold standard involves identifying microfilariae in a night blood smear, as microfilariae exhibit nocturnal periodicity (they are most abundant in peripheral blood at night).
• Antigen Detection Tests: Immunochromatographic Card Test (ICT) or Enzyme-Linked Immunosorbent Assay (ELISA) can detect circulating filarial antigens, which are present even when microfilariae are not. These tests are useful for confirming active infection, especially in areas with Wuchereria bancrofti.
• Ultrasound: Can visualize adult worms in dilated lymphatic vessels, particularly in the scrotum of men with hydrocele (known as "filarial dance sign").
• Polymerase Chain Reaction (PCR): Molecular diagnostic methods can detect filarial DNA, offering high sensitivity.

Treatment:

Treatment aims to kill the parasites and manage the chronic manifestations.

• Antiparasitic Drugs (Mass Drug Administration - MDA):
  • Diethylcarbamazine (DEC): The primary drug, effective against both microfilariae and adult worms.
  • Albendazole: Often administered in combination with DEC or ivermectin. It is effective against intestinal worms and can have macrofilaricidal (adult worm killing) effects in combination.
  • Ivermectin: Used in combination with albendazole or DEC, particularly effective against microfilariae. The triple drug therapy (IDA - Ivermectin, Diethylcarbamazine, Albendazole) is being used in some endemic regions for accelerated elimination efforts.
  • MDA involves administering a single dose of antifilarial drugs annually to entire at-risk populations for several years to interrupt transmission.
• Morbidity Management and Disability Prevention (MMDP):
  • Hydrocelectomy: Surgical removal of the hydrocele.
  • Lymphedema Management: Includes hygiene measures (washing affected limbs, treating skin infections), limb elevation, exercise, and compression therapy to reduce swelling and prevent progression.
  • Management of acute attacks involves pain relief, antibiotics for secondary bacterial infections, and anti-inflammatory drugs.

Preventive Measures:

Prevention focuses on interrupting the transmission cycle and protecting individuals from mosquito bites.

• Vector Control:
  • Spraying insecticides to kill adult mosquitoes (Indoor Residual Spraying - IRS).
  • Larvicidal measures to destroy mosquito breeding sites (e.g., stagnant water bodies).
  • Using mosquito nets (preferably insecticide-treated bed nets).
  • Environmental management to reduce mosquito breeding sites (e.g., draining stagnant water, proper waste disposal).
• Mass Drug Administration (MDA) Programs:
  • Administering antifilarial drugs to entire populations in endemic areas once a year for 4-6 years to clear microfilariae from the blood of infected individuals, thus preventing transmission to mosquitoes.
  • India's National Programme for Elimination of Lymphatic Filariasis employs MDA as a cornerstone strategy.
• Personal Protection:
  • Using insect repellents (e.g., DEET-based).
  • Wearing long-sleeved clothing and trousers, especially during peak mosquito biting hours (dusk and dawn).
  • Screening windows and doors to prevent mosquito entry into homes.
• Health Education and Awareness:
  • Educating communities about the disease, its transmission, symptoms, and the importance of participating in MDA and adopting preventive measures.