Lymphatic Filariasis

Hi!

This is a short piece focusing on a VERY interesting parasitic disease you may never have heard about!

So, what are parasites?

The Centres of Disease Control and Prevention (CDC) define a parasite as an organism that lives in or on another organism (the host). The parasite depends on this organism to survive - gaining food/ nutrients from or at the expense of the host [1].

Parasites cause huge amounts of disease around the world; they are most prevalent in the tropical and subtropical regions of the world in addition to more temperate climates [1].

Lymphatic Filariasis

Today we will focus on a disease called Lymphatic Filariasis (LF). LF is classified as Neglected Tropical Disease (NTD), these are a group of diseases that have lack of attention from the public health community!

LF is a disease caused by filarial parasites that have been transmitted by mosquitoes [2]. The main species of parasite responsible for the disease are Wuchereria bancrofti, Brugia malayi, followed by Brugia timori making up the remainder of cases - approximately 10% [2]

Image: Lauren Murrell

Transmission and Lifecycle

Key

L1: life stage 1

L3: life stage 3

MF: microfilariae

As shown in the image above, the infective stage is when the parasite larvae are at life stage 3 (L3). At this point in their lifecycle they are injected into the human host by the mosquito- whilst it takes blood meal. Once in the body the larvae develop into adult worms, they reproduce, resulting in microfilariae (MF) (early stage parasites) that migrate to the blood and are ingested by mosquitoes, allowing the lifecycle to start again.

Burden of disease

So how widespread is the burden of disease? In 2018, WHO reported that 893 million people in 49 countries were at risk of the disease, and as a result required preventative drug treatment [2]. In 2000 over 120 million people were infected with 40 million having serious symptoms of the disease [2]. Some of these extremely unpleasant symptoms include

1. Lymphoedema: an early symptom of disease includes swelling of tissue mainly in the lower limbs [3]

2. Elephantiasis: a chronic stage of disease due to the obstruction of lymphatic vessels [4]

3. Hydrocele: a common manifestation due to fluid accumulation around the testis [5]

These major symptoms not only impact the physical well-being of afflicted individuals, there is also impact mentally often accompanied with the inability to work and stigma associated.

Global focus on LF

Though it is classified as an NTD, it has been under focus for relatively long time now. The disease was targeted for elimination in 1997 by WHO, in what is known as The Global Programme to Eliminate Lymphatic Filariasis (GPELF) [6]. Though this target has not been reached, encouraging steps have been made with elimination being declared in China and the Republic of Korea in addition to other endemic countries implementing surveillance and interventions to aid progression to elimination [7]. More recently in March of 2020, the WHO declared that Malawi has eliminated LF - a fantastic achievement !

-L

Get in touch !

We would love to hear from you! If there are any diseases you are curious about and would like us to cover feel free to send us an email and we may cover it in an upcoming post!

Want to know more? Check out these links for some more information:

[1] Centres for Disease control and Prevention, (2021) https://www.cdc.gov/parasites/about.html

[2] World Health Organisation, (2021) https://www.who.int/news-room/fact-sheets/detail/lymphatic-filariasis

[3] Shenoy, R.K., (2008). Clinical and pathological aspects of filarial lymphedema and its management. The Korean journal of parasitology, 46(3), p.119. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2553332/

[4] Tada, I., (2011). Pathogenesis and treatment of chronic symptoms with emphasis on chyluria and elephantiasis. Tropical medicine and health, 39(1 Suppl 2), p.47. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3153157/

[5] Norões, J. and Dreyer, G., (2010). A mechanism for chronic filarial hydrocele with implications for its surgical repair. PLoS Negl Trop Dis, 4(6), p.e695. Available at: https://www.ncbi.nlm.nih.gov/pmc/articles/PMC2879368/

[6] World Health Organisation 2020, (d) Global Programme to Eliminate Lymphatic Filariasis Available at: https://www.who.int/lymphatic_filariasis/elimination-programme/en/

[7] World Health Organisation, (2020)(e), Global Progress Towards Elimination, NTD Roadmap Target: Global Elimination as a Public Health Problem by 2020, Available at: https://www.who.int/lymphatic_filariasis/global_progress/en/