Lymphatic Filariasis
Lymphatic Filariasis is an infection caused by microscopic worms, transmitted to humans by the bite of an infected mosquito.
Infection is usually acquired in childhood causing hidden damage to the lymphatic system.
What is Lymphatic Filariasis?
Lymphatic Filariasis is an infection caused by microscopic worms, transmitted to humans by the bite of an infected mosquito.
Infection is usually acquired in childhood causing hidden damage to the lymphatic system.
How dangerous is Lymphatic Filariasis?
Lymphatic Filariasis infection can lead to permanent disability from swollen limbs and breasts called lymphedema, damage to the genitals called hydrocele or swollen limbs with thickened, hardened skin called elephantiasis.
The painful and profoundly disfiguring visible manifestations of the disease occur later in life and can lead to permanent disability.
Patients are not only physically disabled, but suffer mental, social and financial losses contributing to stigma and poverty.
Who is at risk?
Over a billion people are at risk in 73 countries but many mosquito bites over several months to years are needed to get lymphatic filariasis.
Short-term tourists have a very low risk.
How many people are affected by Lymphatic Filariasis?
In 2000 over 120 million people were infected, with about 40 million disfigured and incapacitated by the disease.
Where is Lymphatic Filariasis found?
Lymphatic filariasis is found in 73 countries throughout the tropics and sub-tropics of Asia, Africa, the Western Pacific, and parts of the Caribbean and South America.
In the Americas, only four countries are currently known to be endemic: Haiti, the Dominican Republic, Guyana and Brazil.
How do people get Lymphatic Filariasis?
The infection spreads from person to person by mosquito bites.
A wide range of mosquitoes can transmit the parasite, depending on the geographic area. In Africa, the most common vector is Anopheles and in the Americas, it is Culex quinquefasciatus. Aedes and Mansonia can transmit the infection in the Pacific and in Asia.
What are the signs and symptoms of Lymphatic Filariasis?
Lymphatic filariasis infection involves asymptomatic, acute, and chronic conditions.
The majority of infections are asymptomatic, showing no external signs of infection. These asymptomatic infections still cause damage to the lymphatic system and the kidneys, and alter the body's immune system. Asymptomatic patients do not know they have lymphatic filariasis unless tested.
A small percentage of persons will develop lymphedema. This is caused by fluid collection because of improper functioning of the lymph system resulting in swelling. This mostly affects the legs, but can also occur in the arms, breasts, and genitalia. Most people develop these symptoms only years after being infected.
How is the disease developing?
The swelling and the decreased function of the lymph system make it difficult for the body to fight germs and infections so patients will have more bacterial infections in the skin and lymph system. This causes elephantiasis, a hardening and thickening of the skin. Many of the bacterial infections can be prevented with appropriate skin hygiene and exercise.
Men can develop hydrocele or swelling of the scrotum due to infection with one of the parasites that causes Lymphatic Filariasis specifically W. bancrofti .
Filarial infection can also cause tropical pulmonary eosinophilia syndrome which is typically found in Asian patients. Symptoms of tropical pulmonary eosinophilia syndrome include cough, shortness of breath, and wheezing.
How is Lymphatic Filariasis diagnosed?
Lymphatic Filariasis is diagnosed via the identification of microfilariae in a blood smear by microscopic examination.
More in-depth information:
The microfilariae that cause lymphatic filariasis circulate in the blood at night which is called nocturnal periodicity. Therefore blood collection should be done at night to coincide with the appearance of the microfilariae, and a thick smear should be made and stained with Giemsa or hematoxylin and eosin.
Serologic techniques provide an alternative to microscopic detection of microfilariae for the diagnosis of lymphatic filariasis. Patients with active filarial infection typically have elevated levels of antifilarial IgG4 in the blood and these can be detected using routine assays.
Because lymphedema may develop many years after infection, lab tests are most likely to be negative with these patients.
How is Lymphatic Filariasis treated?
In areas where Lymphatic Filariasis is common, treatment of indi-viduals with anti-parasitic drugs like albendazole donated by Glax-oSmithKline plus either MectizanTM donated by Merck & Co., Inc. or low-cost diethylcarbamazine (DEC) donated by Eisai annually for at least five years can break the cycle of transmission.
Even after the adult worms die, lymphedema can develop. Prevent-ing the lymphedema from getting worse is possible by following several basic principles:
- carefully washing the swollen area with soap and water every day
- elevating and exercising the swollen arm or leg to move the fluid and improve the lymph flow
- disinfecting any wounds using antibacterial or antifungal cream
How can I prevent infection?
Avoiding mosquito bites is the best form of prevention.
The mosquitoes that carry the microscopic worms usually bite between dusk and dawn.
People living in or traveling to an area with lymphatic filariasis should:
- sleep under a mosquito net
- wear long sleeves and trousers
- use mosquito repellent on exposed skin between dusk and dawn
Additionally vector control should be performed while annual mass treatment can reduce the level of microfilariae in the blood and thus, diminish transmission of infection. This is the basis of the global campaign to eliminate lymphatic filariasis.
6.7 billion treatments have been delivered to stop the spread of infection since 2000.
More in-depth information:
Surgery can alleviate most cases of hydrocele.
Severity and progression of the disease, including acute inflammatory episodes, can be reduced and prevented with simple measures of hygiene, skin care, exercise, and elevation of affected limbs.
People with lymphoedema must have access to continuing care throughout their lives, both to manage the disease and to prevent progression to more advanced stages.
The GPELF aims to provide access to a minimum package of care for every person with associated chronic manifestations of lymphatic filariasis in all areas where the disease is present.
Success in 2020 will be achieved if patients have access to the following minimum package of care:
- treatment for episodes of adenolymphangitis (ADL)
- guidance in applying simple measures to manage lymphoedema and hydrocele to prevent disease progression and debilitating, in-flammatory episodes of ADL
- surgery for hydrocele
- treatment of infected persons with antifilarial medicines
How is Lymphatic Filariasis transmitted?
There are three different filarial species that can cause lymphatic filariasis in humans:
- Wuchereria bancrofti, which is responsible for 90 percent of the cases
- Brugia malayi, which causes most of the remainder of the cases
- Brugia timori
The infection spreads from person to person by mosquito bites.
Microfilariae circulate in the person's blood and infect the mosquito when it bites a person who is infected. The microfilariae then grow and develop in the mosquito. When the mosquito bites another person, the larval worms pass from the mosquito into the human skin, and travel to the lymph vessels. Within six months or more they grow into adult worms which live for about five to seven years. The adult worms mate and release millions of microfilariae into the blood. People with microfilariae in their blood then serve as a source of infection to others.
How can the vector be controlled?
A wide range of mosquitoes can transmit the parasite, depending on the geographic area. In Africa, the most common vector is Anopheles and in the Americas, it is Culex quinquefasciatus. Aedes and Mansonia can transmit the infection in the Pacific and in Asia.
- Culex mosquito is widespread across urban and semi-urban areas
- Anopheles is mainly found in rural areas
- Aedes is mainly in endemic islands in the Pacific
Mosquito control is a supplemental strategy supported by WHO. It is used to reduce transmission of lymphatic filariasis and other mosquito-borne infections. Depending on the parasite-vector species, measures such as insecticide-treated nets, indoor residual spraying or personal protection measures may help protect people from infection.
The use of insecticide-treated nets in areas where Anopheles is the primary vector for filariasis enhances the impact on transmission during and after MDA.
Vector control has in select settings contributed to the elimination of lymphatic filariasis in the absence of large-scale preventive chemotherapy.
What are the difficulties and challenges in combating Lymphatic Filariasis?
- maintaining and consolidating advances made in disease control
- enhancing access to diagnosis and treatment for millions of infected people
What programs exist against Lymphatic Filariasis?
A global campaign to eliminate lymphatic filariasis as a public health problem is under way in more than 50 countries.
The elimination strategy is based on annual treatment of whole communities with combinations of drugs that kill the microfilariae.
As a result of the contributions of these drugs by the companies that make them
- GlaxoSmithKline donates Albendazole
- Merck donates MectizanTM
- Eisai donates low-cost Diethylcarbamazine (DEC)
tens of millions of people are being treated each year.
Since these drugs also reduce levels of infection with intestinal worms, benefits of treatment extend beyond lymphatic filariasis.
499 million people no longer require preventive chemotherapy due to successful implementation of WHO strategies.
More in-depth information:
World Health Assembly resolution WHA50.29 encourages Member States to eliminate lymphatic filariasis as a public health problem. In response, WHO launched its Global Programme to Eliminate Lymphatic Filariasis (GPELF) in 2000.
In 2012, the WHO neglected tropical diseases roadmap reconfirmed the target date for achieving elimination by 2020. WHO’s strategy is based on two key components:
- stopping the spread of infection through annual treatment of all eligible people in an area or region where infection is present
- alleviating the suffering caused by lymphatic filariasis through increased morbidity management and disability prevention activities.
Elimination of lymphatic filariasis is possible by stopping the spread of the infection through preventive chemotherapy. The WHO recommended preventive chemotherapy strategy for lymphatic filariasis elimination is mass drug administration (MDA). MDA involves a combined dose of two medicines given annually to an entire at-risk population in the following way: albendazole (400 mg) together with either ivermectin (150-200 mcg/kg) or with diethylcarbamazine citrate (DEC) (6 mg/kg).
These medicines have a limited effect on adult parasites but effectively reduce the density of microfilariae in the bloodstream and prevent the spread of parasites to mosquitoes. MDA can interrupt the transmission cycle when conducted annually for 4–6 years with effective coverage of the total population at risk. Salt fortified with DEC has also been used in a few settings to interrupt the transmission cycle.
From 2000 to 2015, 6.7 billion treatments were delivered to more than 850 million people at least once in 66 countries, considerably reducing transmission in many places. The population requiring MDA has declined by 36% or 499 million where infection prevalence has been reduced below elimination thresholds.
The overall economic benefit of the program during 2000-2007 is conservatively estimated at US$ 24 billion.
Now with14 years of MDA, at least US$ 100.5 billion of economic loss will be avoided over the lifetime of cohorts who have benefited from treatment.
Cambodia, The Cook Islands, Maldives, Marshall Islands, Niue, Sri Lanka, Thailand, Togo, and Tongaand Vanuatu were acknowledged as achieving elimination of lymphatic filariasis as a public health problem.
Eleven additional countries have successfully implemented recommended strategies, stopped large-scale treatment and are under surveillance to demonstrate that elimination has been achieved.
Preventive chemotherapy is still required in 52 countries but has not been delivered to all endemic areas as of the end of 2016.
What does Bayer contribute to the fight against Lymphatic Filariasis?
Bayer has been successfully developing vector control products for decades (see below).
- Currently, the two most relevant Vector Control methods for fighting mosquito-borne diseases are Space Spray applications and breeding sites management. Bayer is a major supplier of Space Spray products since decades.
- A major issue is the build-up of mosquito resistance to the different active ingredient they have been exposed to. Most products used since many years are now facing this situation.
During the last six years Bayer researchers have developed an innovative approach for fighting resistance build-up. They are bringing to market a range of mosquito insecticides that combine two different modes of action, In particular, the new Fludora™ Co-Max Space Spray includes also a new chemistry family. This solution will associate robustness to resistance build up as well as excellent efficacy.
- Thanks to an innovative polymere formulation, Bayer has also launched a totally new type of intervention, Targeted Outdoor Residual Spray (TORS) . This type of application rolled out is South East Asia id particularly adapted to an urban environment. The product is marketed under the brand KOthrne™ Polyzone.
Additionally Bayer has devised an education tool – Mosquito Control Learning Lab – an online learning platform that explains which diseases are transmitted by mosquitos, how they spread and how individuals can protect themselves against mosquito bites. The platform is interactive, testing users in their knowledge and skills in real life scenarios.
Bayer Mosquito Control Learning Lab can be accessed on any computer or tablet and is found here:
https://www.environmentalscience.bayer.ph/Fight-Dengue
Besides this Bayer can look back on products that are still supplied in many parts of the world where resistance to pyrethroid insecticides is not yet established:
- Since 1990s: Aqua K-Othrine™ and Aqua Reslin™ Super are launched. These are the first space sprays to employ a new technology, Film Forming Aqueous Spray Technology (FFAST), and are used to combat adult mosquitos in flight outdoors without releasing volatile hydrocarbons.
- Since 2015: DeltaGard™ launched in the United States. The space spray can be used at 80 times lower doses than comparable products. DeltaGard™ is currently the only product in its class that does not contain volatile organic compounds (VOCs) and is water-based. It was awarded the rarely conferred reduced-risk product classification by the U.S. Environmental Protection Agency (EPA).
What is the societal burden of Lymphatic Filariasis?
Those with severe symptoms of the disease are often unable to work and may suffer significant social stigma as a result of their disfigurement. Many are ostracized or even shunned by those in their communities.
Example study:
The health and economic benefits of the global program to eliminate lymphatic filariasis (2000–2014)
36 million chronic cases will be averted as a result of the first 15 years of the GPELF. This corresponds to 175 million DALYs being averted over the full lifetime of those who have received treatment through the GPELF.
As a result of the first 15 years of the GPELF, 46 million individuals will experience economic benefits due to prevented clinical disease. Individuals treated through the GPELF are estimated to save a combined total of US$96.9 billion (an average of US$2,095 per person) over their lifetime, income that would have otherwise been lost due to inability to work and medical expenses. This is equivalent to the income earned from working 33.3 days (or 11% of their average annual income).
In addition to the economic benefits to individuals, US$3.5 billion in health system costs will be saved in endemic areas. Such savings are critical for health systems in resource-poor settings.
The total economic impact (for both individuals and health systems) is estimated to be US$100.5 billion.
In addition to the health and economic benefits discussed above, the GPELF has had a sizeable impact on quality-of-life at the individual level through amelioration of debilitating, disabling, and stigmatising symptoms.
The GPELF has also likely had a significant impact on the control of co-endemic diseases (such as the soil-transmitted helminths (STH) and scabies) which are sensitive to drug use – meaning that the total health and economic value of the GPELF is likely even greater than what is presented here.
Further info:
➞ link to: Understanding the community impact of lymphatic filariasis/ a review of the sociocultural literature
How did the history of the disease proceed?
- in the 16th century the first documentation of symptoms occurred when Jan Huyghen van Linschoten wrote about the disease during the exploration of Goa. Similar symptoms were reported by subsequent explorers in areas of Asia and Africa, though an understanding of the disease did not begin to develop until centuries later.
- in 1866, Timothy Lewis, building on the work of Jean Nicolas Demarquay and Otto Henry Wucherer, made the connection between microfilariae and elephantiasis, establishing the course of research that would ultimately explain the disease
- in 1876, Joseph Bancroft discovered the adult form of the worm.
- in 1877, the lifecycle involving an arthropod vector was theorized by Patrick Manson, who proceeded to demonstrate the presence of the worms in mosquitoes, but Manson incorrectly hypothesized that the disease was transmitted through skin contact with water in which the mosquitoes had laid eggs
- in 1900, George Carmichael Low determined the actual transmission method by discovering the presence of the worm in the proboscis of the mosquito vector