Leishmaniasis Life cycle, Treatment, Symptoms, Diagnosis, Prevention, Types, Distribution.

Leishmaniasis are flagellated protists that cause a group of several human diseases collectively called leishmaniasis. Leishmaniasis also known as kala azar.

There are different types of leishmaniasis such as cutaneous (skin associated ulcers that heal), diffuse cutaneous (disseminated and chronic skin lesions), mucocutaneous (ulcers of the skin, mouth, nose, and throat), and visceral (affecting liver, spleen, and blood).

Classification of Leishmania

Domain:	Eukaryota
Phylum:	Euglenozoa
Class:	Kinetoplastid
Order:	Trypanosomatida
Genus:	Leishmania

Leishmaniasis

• Leishmaniasis is a parasitic disease.
• The parasite Leishmania is responsible for this disease.
• It is a genus of trypanosomes.
• The disease is mainly found in the tropics, subtropics, and southern Europe.
• The disease is mainly transmitted through the bite of infected sand flies mainly the genus of Phlebotomus (Old World) and Lutzomyia (New World). Sandflies are about one-third the size of a mosquito, so they are hard to see and hear.
• They can transmit from animals to humans or between humans by sand flies.
• There are about 93 species of sandfly worldwide which are proven as the vector of Leishmaniasis.
• Leishmaniasis is divided into different groups among them cutaneous leishmaniasis and visceral leishmaniasis is most common. In visceral leishmaniasis, several internal organs such as spleen, liver, and bone marrow are affected whereas cutaneous leishmaniasis causes skin sores.
• They infect vertebrates, hyraxes, canids, rodents, and humans.
• Currently, In 98 countries a total of 6 million people are affected by Leishmania.
• Approximately 700,000 to 1.2 million or more new cases of cutaneous leishmaniasis are estimated per year.
• The number of new cases for visceral leishmaniasis per year may have decreased to <100,000, but previous estimates ranged up to 400,000 or more cases.
• There are about 21 species of Leishmania that are responsible for Leishmaniasis.

Leishmaniasis distribution

• The disease is mainly found in 88 countries worldwide where approximately 350 million people live. Most of them are tropical and subtropical countries.
• The disease is also found in rain forests of Central and South America and in deserts of West Asia.
• More than 90% of the world’s cases of visceral leishmaniasis are found in India, Bangladesh, Nepal, Sudan, and Brazil.
• Leishmaniasis is mainly found in;
  • Mexico
  • Central America
  • South America—from northern Argentina to Texas (not in Uruguay, Chile, or Canada), southern Europe (leishmaniasis is not common in travelers to southern Europe), Asia (not Southeast Asia), the Middle East, and Africa (particularly East and North Africa, with some cases elsewhere).

Leishmaniasis Structure

• Leishmaniasis parasites are unicellular eukaryotic cells.
• They contain a well-defined nucleus and other cell organelles such as kinetoplasts and flagella.
• Leishmania species exhibit two structural variants during their life cycle such as; the amastigote, and promastigote.
• Amastigote
  • The amastigote form of Leishmania is located within the mononuclear phagocytes and circulatory systems of humans. It is oval-shaped. The size of amastigote is 3–6 µm in length and 1–3 µm in breadth. 
  • The amastigotes are intracellular and nonmotile.
  • Amastigotes are devoid of external flagella. At the anterior part of the amastigote, a short flagellum is embedded without projecting out.
  • The kinetoplast and basal body lie towards the anterior end.
• Promastigote
  • The promastigote form of Leishmania is located within the alimentary tract of sandflies. It is larger and highly elongated. The size is about 15-30 µm in length and 5 µm in width.
  • The promastigotes are extracellular and motile.
  • The promastigote is spindle-shaped, tapering at both ends.
  • At the anterior end, a long flagellum is projected externally.
  • The kinetoplast and the basal body lie in front of the nucleus whereas  the nucleus lies at the centre.

Leishmania species

There are different species of Leishmania all of them are listed in below table;

L. aethiopica	L. amazonensis
L. venezuelensis	L. waltoni
L. turanica	L. tropica
L. tarentolae	L. (Viannia) shawi
L. pifanoi (status disputed)	L. (Viannia) peruviana
L. (Viannia) panamensis	L. (Viannia) naiffi
L. mexicana	L. (Mundinia) martiniquensis
L. (Mundinia) macropodum	L. major
L. (Viannia) lainsoni	L. killicki (status disputed)
L. infantum	L. (Viannia) guyanensis
L. gerbili	L. garnhami (status disputed)
L. forattinii (status disputed)	L. (Mundinia) enriettii
L. donovani	L. chagasi (syn. L. infantum)
L. (Viannia) braziliensis	L. aristedesi (status disputed)
L. archibaldi (starus species)	L. arabica

Leishmania life cycle

The life cycle of Leishmania is begun with the bite of an infected female phlebotomine sandflies.

• During blood meals, the sandflies inject the infective stage or promastigotes within the blood.
• Macrophages and other mononuclear phagocytic cells phagocytes the promastigotes that reach the puncture wound.
• Within these cells, the Promastigotes are transformed into the amastigotes.
• After that, the amastigotes multiplied by simple division and started to infect other mononuclear phagocytic cells.
• The infection would be symptomatic and whether cutaneous or visceral leishmaniasis depends on the Parasite, host, and other factors.
• When a sandfly bites an infected person they get infected by ingesting infected cells.
• Inside the gut of sandflies, the amastigotes transform into promastigotes and migrate to the proboscis.

Leishmaniasis prevention

There are no available vaccines or drugs to prevent infection. The most effective way to prevent leishmaniasis is to protect themselves from sand fly bites. Follow the following rules to decrease the risk of being bitten;

When outdoors 

• Wear long-sleeved shirts, long pants, socks, and tuck your shirt into your pants to reduce the amount of exposed (uncovered) skin.
• Use insect repellent special that contain DEET (N,N-diethylmetatoluamide) to exposed skin such as under the ends of sleeves and pant legs.

In indoors

• Sleep in a well-screened or air-conditioned room.
• Spray insecticide in living/sleeping rooms to kill the insects.
• Use higher floors of a building to sleep because they are poor fliers.
• Use fans in sleeping areas which makes it more difficult for the insects to fly.
• Use a bed net and tuck into your mattress.

Leishmaniasis symptoms

The symptoms depend on the types of Leishmaniasis such as;

Cutaneous leishmaniasis

The characteristic symptom of Cutaneous leishmaniasis is painless skin ulcers. It takes a few weeks to appear after being bitten by an infected sandfly. 

Mucocutaneous leishmaniasis

It takes one to five years after the skin lesions to develop symptoms. The symptoms are;

• ulcers in their mouth and nose or on their lips.
• runny or stuffy nose
• nosebleeds
• difficulty breathing

Visceral leishmaniasis

The symptoms of Visceral leishmaniasis are;

• weight loss
• weakness
• fever that lasts for weeks or months
• enlarged spleen
• enlarged liver
• decreased production of blood cells
• bleeding
• other infections
• swollen lymph nodes

Leishmaniasis diagnosis

Leishmaniasis can be diagnosed by examining the tissue specimens from skin sores (for cutaneous leishmaniasis) or from bone marrow (for visceral leishmaniasis). The tissue sample is examined under a microscope, in special cultures, and by molecular tests.

The presence of an antibody in a blood sample can be helpful for the detection of visceral leishmaniasis.

Leishmaniasis treatment

Amphotericin B (Ambisome) can be used to treat Leishmaniasis. There are different treatment methods based on the types of diseases such as;

1. Cutaneous leishmaniasis:
   1. It can be healed without any treatment, but treatment can increase the healing speed and reduce scarring. It also decreases the risk of further disease. 
   2. Sometimes required plastic surgery where skin ulcers that cause disfigurement.
2. Mucocutaneous leishmaniasis
   1. Treatment is required for Mucocutaneous leishmaniasis, it doesn’t heal naturally. 
   2. For treatment of mucocutaneous leishmaniasis two Antiparasitic drugs can be used such as Liposomal amphotericin B and paromomycin.
3. Visceral leishmaniasis
   1. Sodium stibogluconate (Pentostam), amphotericin B, paromomycin, and miltefosine (Impavido) is used for the treatment of Visceral leishmaniasis.

Leishmaniasis in dogs

• Leishmaniasis disease in dogs is known as the Canine leishmaniasis. It is a zoonotic disease.
• Canine leishmaniasis is transmitted through the bite of an infected phlebotomine sandfly.
• The disease was first found in Europe in 1903

(i) Symptoms of Leishmaniasis in dogs

Cutaneous Leishmaniasis in dogs

The symptoms of Cutaneous Leishmaniasis in dogs are Alopecia, Skin lesions, Ulcerative or exfoliative dermatitis, 

Visceral Leishmaniasis in dogs

The symptoms are Epistaxis (nose bleeds), Kidney failure > increased urination and drinking, Ocular signs, Progressive loss of weight with decreased appetite, Swollen lymphnodes.

(ii) Causative Agent of Leishmaniasis in dogs

Old World:

In Old World the Leishmaniasis is transmitted through sandflies of the genus Phlebotomus. L. donovani in Sri Lanka and L. infantum in the United States are responsible for Leishmaniasis in dogs.

New World:

In new World the Leishmaniasis is transmitted through Lutzomyia.  Leishmania donovani complex, including L. infantum, L. chagasi and L. donovani are responsible for canine visceral leishmaniasis.

Dogs does not contains any Mexicana (L. mexicana, L. amazonensis, L. venezuelensis, and L.  pifanoi) and Viannia (L. braziliensis, L. guyanensis, L. panamensis and L. peruviana) strains. 

(iii) Transmission of Leishmaniasis in dogs

• The disease is directly transmitted from sandfly to dog.
• A study in the US found L. infantum can be transmitted from dog to dog by direct contamination with blood and secretions.

(iv) Diagnosis of Leishmaniasis in dogs

For detection of Leishmaniasis in dogs different diagnosis tests are performed such as molecular biology and genetic techniques. The results of these techniques are highly specific and accurate.

ELISA and Polymerase Chain Reaction (PCR) are the most commonly employed methods in medical laboratories for detection of Leishmaniasis in dogs.

(vi) Treatment of Leishmaniasis in dogs

There is no cure for canine leishmaniasis, but different treatment methods are used by different countries. Different treatment methods are used based on the geographic area, strain of infection and exhibited symptoms such as;

• L. donovani: Antimony resistant so amphotericin B is recommended
• L. infantum: Amphotericin B, Meglumine antimoniate, Miltefosine, Allopurinol.

FAQ on Leishmaniasis

Further Reading

• Protozoa Definition, Classification, Characteristics, Structure, Diseases, Examples
• Amoeba Cell Characteristics, Structure, Movement, Nutrition, Reproduction, Disease, Habitat.