Lymphatic Filariasis is a disease that is on the World Health Organization's (WHO) top ten list of diseases to eliminate by 2020. Left untreated and undetected, it can lead to a condition called Elephantiasis. The name comes from the severe swelling of the limbs that occurs during the chronic state of the disease. It is transmitted via mosquitoes to humans in tropical and sub-tropical climates and it is endemic in a large number of countries around the world. Prevention is possible via some very basic methods and early detection and treatment can prevent long-term consequences associated with the disease.
Lymphatic Filariasis is a little known disease in the United States but it is on the World Health Organization's top ten list of diseases to eliminate along with Malaria and leprosy (Narain, J.P., Dash, A.P., Parnell, B., Bhattacharya, S.K., Barua, S., Bhatia, R. et al., 2010). A large portion of the population of the planet is at risk of contracting this often debilitating disease.
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Lymphatic Filariasis is also referred to as Bancroft's Filariasis and Elephantiasis when the disease it has progressed to its chronic state. (Elephantiasis, 2010).
The main causative organism is a microscopic parasitic roundworm. There are three different types of this worm: Wuchereria bancrofti (most common and makes up 90% of all cases), Brugia malay and Brugia timori (Longe, 2006). Wuchereria bancrofit lives in warm regions on every continent except North America (Callahan, 2002). Brugia malayi is primarily found in India, Southeast Asia and Indonesia (Callahan, 2002). Brugia timori is found to a very limited extent in Timor.
The disease has two stages, acute and chronic. When the disease is in the acute phase, the symptoms usually include a recurring fever and infections of the lymph vessels or nodes in the arms, legs or genitals which can lead to severe and permanent swelling of the lymph vessels and secondary infections (Elephantiasis, 2010). In the chronic stage, the worms block the lymphatic areas of the limbs which cause overgrowth of the limb or body part because the lymphatic system is not able to perform its function of draining fluid out of the area (Callahan, 2002). Males may also have swelling in the scrotum. This is how the disease gets the name of Elephantiasis because the limbs enlarge to the point where they resemble elephant limbs and the skin takes on a rough texture like elephant skin (Ferrara, 2010).
The precise mechanism that causes the pathology of the disease is not known and some people who are infected may not show any signs or symptoms for many months and sometimes even years (Rajan, 2003). The parasite apparently only infects humans and has never been found to affect animals. The parasite migrates to the lymphatic vessels and takes up residence. It then matures into the worm over the course of a few months to one year and begin producing the microfilariae which is suspected of causing the initial fevers and chills that are the first symptoms of the disease (Rajan, 2003). Also, if a person is infected once, they may never actually develop any symptoms even though the worm is living in their lymphatic system and the microfilarasia are circulating in their blood. It is repeated exposure with multiple worms along with the worms excretions and blockage of the lymphatic system that seems to cause the disease to progress to its most severe form especially since the worm will normally die sometime after seven year (Rajan, 2003).
Duration of Disease
The duration of Lymphatic Filariasis varies depending on the number of re-infections suffered by a host. A person with Elephantiasis can live with the disease and usually dies from complications and secondary infections from the worms both living and dead (Wallace & Kohatsu, 2008). The disease can last a lifetime and can worsen over time if left untreated. The disfiguring growth of the limbs or genitalia is another side effect as well as permanent damage to the lymphatic system, kidneys and secondary infections. There is also a social stigma to the deformities that accompany the chronic stages of the disease. Those who suffer from the disease are often ostracized.
The adult worm normally lives from three to five years and the microfilariae will die after twelve months if not taken up by a mosquito to begin the next phase of the lifecycle (Longe, 2006).
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A person contracts the disease by being bitten by an infected mosquito of the genera Culex, Aedes or Anopheles. The mosquitoes are the intermediate hosts and when they bite someone, they inject the third-stage larvae into the blood of the host (Elephantiasis, 2010). Once injected into a human host, the larvae mature into worms which move to the lymphatic system and after about one year, produce embryo called microfilariae (Callahan, 2002). Adult worms live for about seven years (Ferrara, 2010). It is the buildup of adult worms in the lymphatic system over time that causes lymph fluid to collect which leads to severe swelling of the limbs and groin area (Ferrara, 2010). The microfilariae circulate in the blood stream waiting to be taken up by a mosquito. Interestingly, the microfilariae are at their most active in the blood at night when mosquitoes are also most active (Wallace & Kohatsu, 2008). This increases the chance of being taken up by a mosquito and continuing the lifecycle. When a mosquito bites and infected host, they take up the microfilariae along with the blood. The larvae mature to the second state in the mosquitoes. Repeated exposure and repeated transmission of larvae that can mature into adult worms is usually what brings on the symptoms (Ferrara, 2010). A person who is bitten once and infected may never actually experience any symptoms.
Prevention and Treatment
The disease is being attacked from many angles by the WHO. Those who have an active parasite are normally treated with the drug Diethylcarbamazine (DEC) which will both limit the number of microfilariae in the blood stream and gradually kill the parasite (Lammie, Milner &Houston, 2006). The drug will cause some nausea and vomiting and sometimes fever depending on the level of microfilariae in the blood (Elephantiasis, 2010). However, because the treatment lasts for over one year, it is sometimes difficult to get the needed medical supplies to the areas with the highest incidence in a cost effective manner. Since the drug DEC seems to act as a deterrent as well as a cure, there is a proposal to add DEC to salt for distribution in the affected areas of the world in much the same manner that iodine was added to salt (Lammie, Milner &Houston, 2006). Trials with DEC fortified salt have been carried out in China, Brazil, Haiti, India and Tanzania with great success since DEC laced salt acts as a protective measure as well as providing benefits for those already infected (Lammie, Milner &Houston, 2006).
Other drugs used in treatment include ivermectin and albendazole and more recently doxycycline (Wallace & Kohatsu, 2008). Albendazole will kill the worms but does not have any effect on the microfilaria in the blood so the transmission cycle will continue unless the intermediate host is also reduced or eliminated (Wallace & Kohatsu, 2008). In addition to drug therapies, movement of the affected limbs is encouraged along with antibiotics for any secondary infections caused by damage to the lymphatic system (Ferrara, 2010).
There is little that can be done once the lymphatic swelling has set in other than attempting to force the lymph out via compression bandages (Elephantiasis, 2010). The other alternative is surgery to correct the affected limbs but this is sometimes not cost effective.
Because the causative agent spends a portion of its lifecycle in the mosquito, the preventative measures that are being undertaken include the use of insect repellent and protective clothes in affected areas as well as water treatment to reduce the insect population that transmits the disease to humans (Wallace & Kohatsu, 2008). Other measures include the use of mosquito netting, screens on windows and staying inside after dark when mosquitoes are the most likely to be active (Ferrara, 2010). In addition, while the mosquitoes are being dealt with, the population near the affected area can be given DEC as a preventative treatment so that the cycle of transmission is broken (Elephantiasis, 2010).
Antibiotics have also been shown to be effective in the past but because antibiotics should not have any impact on a nematode, the effect of antibiotics was dropped until recently. There has also been some investigation into the possibility that a certain population of the worms themselves have a bacterial symbiont which is susceptible to the antibiotics (Rajan, 2003). The suspicion is that the two species have become dependent and if the symbiont dies, the host dies as well. If this is proven true, then antibiotics may also be used at some point in the future to treat lymphatic Filariasis in some cases. It is also suspected that some of the inflammation and other secondary infections might actually be caused by the symbiont rather than the nematode.
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Incidence: World, USA and Colorado
Approximately eighty to one-hundred million people in 75 countries around the world are at risk of contracting Lymphatic Filariasis and forty million are in the chronic stages of the disease and suffer from the disfiguring disability known as Elephantiasis (Lammie, Milner, & Houston, 2006). Lymphatic Filariasis occurs primarily in tropical and subtropical countries mostly in coastal areas with high humidity although it also occurs in Japan and China and come European countries (Elephantiasis, 2010). The area with the highest risk is south-East Asia. Lymphatic Filariasis at one point appeared in Charleston, South Carolina until about 1920 but then dies out before World War II (Elephantiasis, 2010). The reason for the disappearance in the United States is due to mosquito control and water sanitation (Elephantiasis, 2010). It occurs in the United States primarily where it has been contracted elsewhere and brought back to the United States (Elephantiasis, 2010). There does not seem to be any incidence of the disease in Colorado primarily because the climate and altitude and mosquito population do not generally offer a good climate for the life cycle.
Mortality Rate: World, USA and Colorado
Lymphatic Filariasis although impacting millions does not have a high mortality rate. The chief issue with the disease is the ongoing illnesses and secondary infections along with lost productivity and economic hardship suffered by those affected. According the World Health Organization, Lymphatic Filariasis is a targeted disease for elimination due to the large number of people at risk (Weekly epidemiological record, 2009). Those who contract the disease can live with it for all or most of their lives and it is the repeated infections via mosquito bites that eventually lead to the progression to the chronic state of the disease and eventual death ((Narain, J.P., Dash, A.P., Parnell, B., Bhattacharya, S.K., Barua, S., Bhatia, R. et al., 2010)
The disease is difficult to detect because the initial infection may not present any symptoms as the worm moves to the lymphatic system and matures. It can also take some time for the Microfilaria to show in the blood in sufficient quantity. The isolation technique will either focus on detecting the adult worm or the microfilariae. Blood samples can be taken and the sheathed microfilaria can be detected in a Giemsa stain which is a stain specifically used for detecting the presence of microfilaria in the blood (Wallace, & Kohatsu, 2008). A methylene azure B. stain is used on the blood sample and if there is microfilaria in the blood, they will appear blue or purple. It is important that this blood be taken in the evening when the microfilaria is most active. The microfilaria can move out of the blood during the day so blood samples taken in daylight hours can sometimes result in false negatives (Longe, 2006). Also, it is possible that an infected person will not have any microfilaria in the blood. The worm itself is very hard to detect because it is buried in the lymphatic system. Another technique used is to look for what is called the "filarial dance sign" in the scrotum (Wallace &Kohatsu, 2008). This is a visible detection of the worm's movements via ultrasound.
Lymphatic Filariasis is a preventable disease that strikes poor countries in tropical and sub-tropical countries. Its debilitating effects have made it a target for elimination in the countries affected. Prevention methods are basic and include proactively spraying for the mosquitoes and treating the population with DEC laced salt or administration of DEC in tablet forms in order to break the cycle of infection. In addition, common precautions against mosquitoes can also be used such as protective clothing, netting and sprays.