Step-by-Step Breakdown of the Leishmania Life Cycle
Leishmania belongs to genus trypanosomes that causes disease leishmaniasis. These genus are spreaded fastly by sandflies, who belonged to the Phlebotomus genus in the old period and now they come under the Lutzomyia genus. About 93 species of sandfly are present in the ecosystem. Most commonly infected hosts by leishmania are hyraxes, canids, rodents and humans and their primary hosts are vertebrates. Parasitic leishmania are commonly known for their multiplying tendency inside sand fly. There are various types of leishmania one among them is visceral leishmania, which is commonly known as Kala-azar and they are most fatal as they cause anemia, weight loss, irregular periods of fever and enlargement in spleen and liver. Another type is cutaneous leishmania and they are commonly present and causes ulcers, skiing damage that causes scars. These species are mostly active during night i.e they are nocturnal in nature and they require humid and warm temperature for their survival.
Classification of Leishmania
Phylum: Protozoans
Order: Kinetoplastids
Family: Trypanosomatidae
Genus: Leishmania
Causing Agents
Leishmaniasis is a vector borne disease that is transmitted by sand flies and they are caused by protozoa named Leishmania. There are more than 20 species of Leishmania which causes human infection they are: L. donovani complex with 2 species (L. donovani, L. infantum [also known as L. chagasi in the New World]); the L. mexicana complex with 3 main species (L. mexicana, L. amazonensis, and L. venezuelensis); L. tropica; L. major; L. aethiopica; and the subgenus Viannia with 4 main species (L. [V.] braziliensis, L. [V.] guyanensis, L. [V.] panamensis, and L. [V.] peruviana). All these species are morphologically the same from one another but can be differentiated from one another by iso enzymes and molecular methods.
Life cycle of Leishmania
Leishmaniasis is caused in two different stages:
1. Sand Fly Stage: In the very first stage infected sand fly find a suitable host for themself and inject the promastigote parasites into the skin during blood meal. Promastigote is also a type of Leishmania which are elongated, flagellated and infective parasites that grow in the midgut of female sandfly for further infection process.
2. Human Stage: After reaching promastigotes into the wound, they are either ingested or phagocytized by macrophage cells. Transformation of the cell into the tissue stage of the parasite is done by promastigotes and this parasite is known as amastigotes. Amastigotes multiply simply by division process. Due to this multiplication process they form large groups, and now they are ready to infect mononuclear phagocytic cells. They show symptoms. After all this when a sand fly finds an infected host, it ingests these infected cells as soon as they sucks blood from the host and by this fly gets infected with the parasite. Development of amastigotes to promastigotes occurs inside the gut of sandflies. After developing, the parasite migrates to the sucking organ of the fly known as proboscis. After arriving at the proboscis, it is only a matter of time when the sandfly bites a human host and passes on the disease leishmaniasis.
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How to Diagnosis Leishmaniasis Disease
There are various laboratory methods by which we can diagnose leishmaniasis disease. Some of them are:
1. From bone marrow we can examine parasites under a microscope, in special culture and by molecular test. Example: for detection of visceral leishmaniasis we can use this method.
2. By blood test we can detect antibodies produced in response to parasites.
Prevention and Control
No vaccines or drugs are available to prevent infection and the best way to stay away from leishmaniasis is preventive measures, some of these preventive measures are given below:
Cover as much skin as you can, to avoid getting in contact with parasites.
Apply skin repellent to exposed skin areas and under the sleeves and pant legs and the most effective repellent is DEET.
FAQs on Leishmania Life Cycle Explained: Key Stages & Transmission
1. What are the two main stages in the life cycle of Leishmania?
The life cycle of the Leishmania parasite is digenetic, meaning it requires two hosts (a sandfly and a mammal) and alternates between two main stages:
- Promastigote: This is the motile, flagellated, and elongated form found in the gut of the female sandfly. It is the infective stage that is transmitted to humans during a blood meal.
- Amastigote: This is the non-motile, round or oval form found inside the macrophage cells of the mammalian host. It is the multiplicative stage within humans that causes the symptoms of leishmaniasis.
2. How is Leishmania transmitted from a sandfly to a human?
Leishmania is a vector-borne parasite transmitted through the bite of an infected female phlebotomine sandfly. The transmission process occurs as follows:
- An infected sandfly, carrying promastigotes in its proboscis, bites a human to take a blood meal.
- During the bite, it injects the promastigotes into the skin.
- These promastigotes are then engulfed by the host's immune cells, specifically macrophages, where they transform into amastigotes and begin to multiply, establishing the infection.
3. What is the difference between the promastigote and amastigote forms of Leishmania?
The promastigote and amastigote forms are structurally and functionally distinct stages adapted to different hosts. The key differences are:
- Host: Promastigotes are found in the invertebrate host (sandfly), while amastigotes are found in the vertebrate host (human/mammal).
- Motility: Promastigotes are motile due to a long, single flagellum. Amastigotes are non-motile and lack an external flagellum.
- Location: Promastigotes are extracellular, living in the sandfly's gut. Amastigotes are intracellular, living inside host macrophages.
- Function: The promastigote is the infective stage for humans, while the amastigote is the replicative or multiplicative stage responsible for the disease pathology.
4. What are the main clinical types of leishmaniasis that affect humans?
Leishmaniasis manifests in several clinical forms, depending on the species of Leishmania and the host's immune response. The three primary types are:
- Visceral Leishmaniasis (VL): Also known as Kala-azar, this is the most severe form. The parasite affects internal organs like the spleen, liver, and bone marrow. It is fatal if left untreated.
- Cutaneous Leishmaniasis (CL): This is the most common form, causing skin lesions, sores, or ulcers on exposed parts of the body, which can lead to scarring.
- Mucocutaneous Leishmaniasis (MCL): This form leads to the partial or total destruction of mucous membranes of the nose, mouth, and throat.
5. Which stage of the Leishmania life cycle is infective for humans, and which is the diagnostic stage?
The roles of the stages are distinct in the context of human infection and diagnosis:
- Infective Stage: The promastigote is the stage that is infective to humans. It is injected into the bloodstream when an infected sandfly takes a blood meal.
- Diagnostic Stage: The amastigote is the diagnostic stage. Diagnosis is confirmed by identifying these non-motile forms within macrophages in tissue samples, typically from a bone marrow, spleen, or lymph node aspirate.
6. What is the scientific classification of the Leishmania parasite?
The genus Leishmania belongs to the protozoan group. Its taxonomic classification, as relevant for the CBSE/NCERT syllabus, is:
- Phylum: Protozoa
- Class: Mastigophora (or Zoomastigophora)
- Order: Kinetoplastida
- Family: Trypanosomatidae
- Genus: Leishmania
7. Why is the Leishmania parasite's life cycle described as 'digenetic'?
The term 'digenetic' means that the parasite requires two different hosts to complete its entire life cycle. For Leishmania, these two hosts are:
- An invertebrate host (the primary host or vector), which is the female phlebotomine sandfly.
- A vertebrate host (the secondary host), which is a mammal, such as a human, dog, or rodent.
The parasite undergoes essential developmental changes and multiplies in both hosts, making both indispensable for its survival and transmission.
