Agent – What is the causative agent? Scientific name? Image? Type of pathogen? Where is it found?
There are three varieties of leishmaniasis–visceral, cutaneous and mucocutaneous. The species that are the causative agent are L. donovani, L. tropica and L. braziliensis respectively. Leishmaniasis is a general medical term which covers all three forms of the disease. The pathogen is a parasite which is often spread by a sand flee bite. Leishmaniasis can have a whole host of risk factors–poverty, malnutrition, deforestation, and urbanization. It is found in predominately tropical and subtropical regions, and the climate could range from deep inside of a South American rain forest to the dry sand deserts of Africa and the Middle East. The vast majority of visceral leishmaniasis cases (90%+) are in India, Bangladesh, Nepal, Sudan, and Brazil.
Image of L. donovani
Image of L. tropica
Image if L. braziliensis
Host – How are humans affected? Which systems are impacted? What treatments are available?
Humans are affected differently based on the variation of the disease. Cutaneous leishmaniasis is the most common form and it causes skin lesions that last for months or even years. These lesions develop weeks to months after the initial expose, making the disease somewhat difficult to trace to a particular event. If a patient develops one lesion, it is likely that he or she will develop more. These open sores often lead to atrophic scarring, and any patient with the disease should seek proper (and complete) treatment. If left completely untreated, then cutaneous leishmaniasis can lead to other forms later on.
Image of a skin lesion from Cutaneous Leishmaniasis
Mucosal leishmaniasis is caused when the parasites are sent from the skin in the cutaneous form to naso-oropharyngeal mucosa. When someone has untreated cutaneous leishmaniasis, it is more likely that they will develop the mucosal form. This version of the disease does not manifest its symptoms until years or decades after the initial cutaneous lesions. The symptoms are usually characterized by unusual nasal stiffness or bleeding, and if left untreated, can lead to the deterioration of the naso-oropharyngeal mucosa.
Visceral leishmaniasis is very broad in its definition, but is definitely the most severe form of leishmaniasis. This version adversely impacts mostly internal organs–more specifically the spleen, liver, and bone marrow. One of the most common symptoms of this disease is an enlarged spleen, which can be palpated in a physical examination. If untreated, visceral leishmaniasis is often fatal. Some people who have visceral leishmaniasis can also develop post kala-azar dermal leishmaniasis (PKDL) which is categorized by skin lesions, mostly on the face, following the treatment of visceral leishmaniasis.
Leishmaniasis can impact the respiratory system (naso-oropharyngeal ), integumentary system (skin lesions), lymphatic system, and the nervous system. Untreated, it can also effect a host of organs as stated earlier.
Treatments for all forms of leishmaniasis involve taking some form of medication. Some commonly prescribed trade-name medicines are Pentostam, AmBisome, and Impavido. The treatment regimen must be followed exactly, and even if followed, can still be unsuccessful in entirely treating the disease. There is no preventative medication someone can take (like anti-malarials)–the only way to prevent the disease while visiting tropical and sub-tropical climates is through a mosquito net. If the net is weaved densely enough, then it will not allow the sand fleas to enter onto skin and subsequently spread the parasites. There are also other ways to deter sand fleas such as higher strength bug repellants like pyrethrins, malathion, or fenchlorvos . These sprays are able to deter many different insects, and oftentimes are effective at repelling them.
Environment – What environmental or behavioral factors result in disease transmission? What environmental or behavioral factors impact treating the disease.
Anyone can contract the disease if they are bitten by sand fleas carrying the required parasite(s), but sand fleas have a certain environment that they prefer to live in. When there is extreme poverty, a large amount of trash, and improperly disposed bodily waste, then the fleas will thrive and be more prevalent. Leishmaniasis can effect people of any socioeconomic class, but it is more likely to occur in areas where people are generally at or below poverty level. This is partially due to the higher amounts of sand fleas in low-income tropical areas, but partially because of the limited access to mosquito nets and insecticides. Once people contract the disease, it is also more dangerous to have with limited to no access to quality healthcare. With a certain perscription regimen, leishmaniasis can often be treated, but many either do not have the disposable income to buy the needed medicines or do not even know what their sickness is. If there are no trained medical professionals, people would have no idea that they needed a certain medicine because they may not even know what the lesions are from. This leads to even more issues because if it is left untreated, then cutaneous could lead to its more severe forms: either mucocutaneous or visceral. If the person who had the disease moves back to a clean environment out of the tropics, then it is unlikely that they would contract it again after it is treated. People foreign to these tropical areas are also more likely to be prepared for protection from sand fleas through either mosquito netting or some powerful insecticide.