Leishmania Life Cycle

Introduction

Leishmania is a parasite of vertebrates belonging to the genus Leishmania and order Trypanosomatida. These infectious parasites are responsible for the vector-borne disease known as leishmaniasis. This disease is transmitted from one person to another with the help of infected sandflies. Leishmania exists in two forms. One is oval and round-shaped and reproduces in the host vertebrate while the other is elongated having flagella and are motile. These are present in the alimentary canal of Sand flies. There are different types of leishmaniasis, namely, cutaneous leishmaniasis, mucocutaneous leishmaniasis, and visceral leishmaniasis. Out of these, cutaneous leishmaniasis is the most common one and it produces ulcers on the skin.

Mucocutaneous leishmaniasis is a rare form and it can spread from skin to mouth, nose, and throat. In severe cases, it can completely or partially spoil the mucous membrane of the affected area. The third type visceral leishmaniasis is commonly known as kala-azar. It shows symptoms approximately 2-8 months after being bitten by sandflies. It affects the spleen, liver, bone marrow, and immune system. It is very dangerous and should be treated immediately after showing symptoms.

Features

As already mentioned, Leishmania species are responsible for diseases in vertebrates including humans, dogs, cattle, sheep, etc., which commonly known as leishmaniasis. The infectious pathogens are fetched up by the sandflies that suck blood.

These infectious species are found in India, South America, China, Mediterranean countries, and parts of Africa. The Leishmania species make their occurrence in WBC, liver cells, and as well as cells of the spleen. These parasites are responsible for fever in humans which is known as Kala-azar. People affected by this disease exhibits enlarged spleen followed by the depletion of WBC cells.

Classification

Kingdom	Animalia
Phylum	Euglenozoa
Subphylum	Sarcomastigophora
Class	Kinetoplastea
Order	Trypanosomatida
Genus	Leishmania
Species	donovani

Life Cycle of Leishmania

• Leishmania needs two hosts to complete its life cycle, a primary and a secondary host for reproduction and development.

• The vertebrates (human being) are the primary hosts where the parasites will be fed and reproduced asexually.

• Secondary host are either invertebrates or blood-sucking insects. In case of Leishmania, it is sand fly.

• In the life cycle of Leishmania reservoir host is also present.

• Parasites do not undergo changes in the reservoir host but wait for the primary host.

Life Cycle in Man

• Leishmania donovani, is an infectious parasite which enters into the human blood through infected sand flies.

• With the help of antenna the effected sand fly suck human blood and transmits the disease.

• Some of the infectious parasites which enter the blood circulation will be ingested and digested by the WBC.

• While other parasites enters into the reticuloendothelial system.

• These parasites now transform into another form and settle in the cells of the reticuloendothelial system.

• Leishmania donovani starts multiplying and as a result of this the cells affected by the parasites enlarge significantly in size.

• The macrophages burst and releases the parasites when the number reaches to 200 or more.

• The released parasites enter into vector flies when ingested for further stages and the cycle continues.

Life Cycle in Sand Flies

• When the sand fly sucks the infected human blood the free parasites enters the vector body along with the blood.

• They are elongated and have flagella. As they have flagella they are motile and enters into sand fly’s alimentary canal.

• After entering the mid gut, the parasites multiply and increase in number during which the sand fly is considered as heavily infected but the salivary glands remain unaffected.

• Later the parasite enters the foregut and again the transmission of parasites to the primary host takes place when the infected fly bite a new host.

Leishmaniasis

Leishmaniasis is a parasitic infection generally caused by protozoa Leishmania donovani. The common diagnosis method is as follows −

Diagnosing Cutaneous Leishmaniasis

• Tissue specimens will be collected through biopsy for the detection of this disease. Sample cells from the ulcers will be extracted and sent for examination.

  By this method, the health practitioner would be able to detect the DNA or genetic material of the disease-causing parasites.

Diagnosing Visceral Leishmaniasis

• Health practitioner will first ask the patient about their travel history.

• Health practitioner first will take a physical examination.

• They may then perform a bone marrow biopsy or take a blood sample for examination.

• A variety of specialized tests aid with diagnosis. Special chemical stains of bone marrow can help identify immune cells infected with the parasite.

Symptoms

• Difficulty in breathing.

• Inflammation of the skin, healing takes a lot of time that later leads to the formation of ulcers.

• Nose bleeding or running nose.

• Fever accompanied by cough. It lasts for weeks or may come and go in a periodic manner.

• Diarrhoea and vomiting.

• Stomach pain.

• Weight loss.

• Sweating particularly at night time.

• Ulcers in mouth, gums, lips, tongue, etc.

Treatment

• Generally, antiparasitic drugs like amphotericin B are used to treat leishmaniasis. The treatment varies among individuals based on the type of leishmaniasis.

• Some cutaneous ulcers do not require any treatment for healing. But proper medication speeds up healing procedure and reduces scar marks and the risk of secondary infection. In case of severe skin ulcers, individuals may need plastic surgery.

• The patient suffering from mucocutaneous leishmaniasis requires treatment. Generally, paromomycin and liposomal amphotericin B are used to treat this type of disease.

• To treat visceral leishmaniasis several medicines are widely used. Some of the common medicines are pentosan, amphotericin B, paromomycin, and impavido.

Prevention

• While going outdoors use insect repellents that contain DEET on the sleeves and pants.

• Wear full sleeve clothes including long socks.

• Use insect repellents at home.

• Spray insect repellents outdoors periodically to avoid the breeding of sand flies.

• Try to avoid going outdoors between dusk and dawn as the sandflies are active at that time.

• The windows and doors should be covered with nets.

• Use nets while sleeping.

Conclusion

Leishmania is an infectious parasite responsible for the vector-borne disease known as leishmaniasis. This disease is transmitted from one person to another with the help of infected sandflies. Leishmania needs two hosts to complete its life cycle. There will be primary and secondary hosts for the parasites. Humans act as a primary host where the parasites will be fed and reproduce asexually. The secondary host is either invertebrates or blood-sucking insects. In Leishmania, it is sand fly.

FAQs

Q1. What do you understand by flagella?

Ans. It is a primary locomotive organ present in unicellular organisms. With the help of flagella, the organism moves from one place to another.

Q2. Name some reservoir hosts?

Ans. Dog, jackals, and ground squirrels are examples of some of the reservoir hosts.

Q3. What are vectors?

Ans. An organism that is responsible for transmitting diseases from one animal to another.

Q4. What is DEET?

Ans. It is an effective insect repellent and its chemical name is NNdiethyl -metatoluamide.

Q5. What is an ulcer?

Ans. It is a blister on the skin or mucous membrane.