LEISHMANIA MEXICANA: CHARACTERISTICS, MORPHOLOGY, DISEASES - BIOLOGY - 2025

Leishmania mexicana is a Euglenozoa of the Kinetoplastea class. It is an obligate parasite that causes the disease known as leishmaniasis. In its life cycle it presents two completely different stages or body shapes, one of them elongated and flagellated and the other rounded or oval and lacking a flagellum.

Besides the difference in shape, these two phases also differ in their habitat. The first one, known as promastigote, is extracellular and multiplies in the intestine of an insect vector; while the second, or amastigote, is intracellular and multiplies within human macrophages.

Promastigote of Leishmania mexicana. Taken and edited from: Zephyris.

Leishmaniasis is a zoonotic disease that can have different species of mammals as reservoirs, generally dogs. It also uses blood-sucking mosquitoes, mainly of the Lutzomyia genus, as intermediate hosts and vectors. Apart from L. mexicana, there are other species of the same genus, all causing the disease.

Leishmaniasis can present in five clinical forms, localized cutaneous (LCL), recurrent (LR), diffuse cutaneous (LCD), mucocutaneous (CML) or spurious, and visceral (LV) or Kala-azar. Leishmania mexicana has been associated with localized and diffuse cutaneous forms.

General characteristics

Morphology

The leishmaniasis parasite has two body forms: promastigote and amastigote:

- Promastigote

It is considered the infective form. It is elongated and flagellated and has a size that will vary depending on the phase in which it is found:

Procyclic promastigote

The length of the body ranges from 6.5 to 11.5 µm. Another characteristic of this phase is that its flagellum is shorter than the body.

Nectomonad promastigote

This phase is responsible for adhering to the microvilli of the epithelial cells. It is longer than 12 µm and the flagellum is slightly shorter than the body.

Lectomado promastigote

The body length ranges from 6.5 to 11.5 µm, while the length of the flagellum is greater than that of the body.

Metacyclic promastigote

It is the form that the insect transmits to the mammal when it bites it to feed. The size of the flagellum is still larger than that of the body, reaching less than 8 µm.

- Amastigote

It constitutes the replicative form. It is round or oval with a diameter that ranges between 2 and 5 μm. It lacks a scourge.

Amastigote of Leishmania mexicana. Taken and edited from: Zephyris.

Lifecycle

In the human being

The life cycle of Leishmania mexicana begins when an infected sandfly bites a mammal (including humans) for food. At that time, it injects metacyclic promastigotes into the skin of the mammalian host.

Promastigotes are phagocytosed by macrophages and dendritic cells. Parasites are not digested, but remain within a parasitophorous vacuole, where they transform into amastigotes and divide by fission.

The multiplication of the parasites causes the lysis of the infected cell, for which the amastigotes are released again to infect new cells and affect the skin tissues.

In the insect

When an uninfected sandfly feeds on a diseased mammal, it ingests macrophages loaded with amastigotes and acquires the infection. The parasites reach the intestine in the form of amastigotes where they will transform into promastigotes.

Promastigotes go through each of the phases of this stage while dividing, until they transform into metacyclic promastigotes that migrate to the proboscis of the insect.

If in this phase the insect bites an uninfected mammal, it will inject the metacyclic promastigotes and a new cycle will begin.

Diseases

Leishmaniasis is a disease produced by different species of Leishmania, and can affect the skin (localized cutaneous leishmaniasis, recurrent and diffuse), skin and mucosa (espundia) or internal tissues (visceral or Kala-azar).

Leishmaniasis, in any of its clinical forms, affects more than 12 million people throughout the world. It is estimated that at least 2 million people are infected annually. Leishmania mexicana has been associated with only two of these clinical forms of the disease.

The main vectors of the disease are sandfly insects of the Lutzomia genus, which reach a maximum size of 4 mm.

Localized cutaneous leishmaniasis

This type of leishmaniasis occurs when amastigotes do not spread beyond the site of the bite, hence the name localized. Sandflies must feed in this area to acquire the parasite. It is the most common form of leishmaniasis. It can heal spontaneously.

Sandfly insect Phlebotomus sp. Taken and edited from: See page for author.

Diffuse leishmaniasis

It is a disseminated and recurrent infection that tends to reappear after the end of treatment. It does not heal spontaneously. The lesions that occur in this type of leishmaniasis are usually asymptomatic, with no tendency to ulcerate. It is a rare form of the disease.

Symptoms

Leishmaniasis can be asymptomatic or present different symptoms, depending on the clinical form, after an incubation period that can range from one week to several years, although the latter is rare.

Localized cutaneous leishmaniasis

The initial signs of the disease consist of the appearance of vascularized itchy papules in the area of ​​the insect bite. Nodules or hyperkeratosis may also appear instead of papules.

Papules appear with raised edges, ulcerate, and may be dry or ooze after a few weeks, forming lesions that occur most frequently on the hands, feet, legs, and face. The injuries are not painful.

Lymph nodes may become swollen, although no elevation of body temperature occurs.

Diffuse leishmaniasis

This type of disease occurs when amastigote spreads through the skin to other tissue and lymphocytes are unable to react to Leishmania antigens (anergy).

The main manifestations are thickening of the skin in the form of plaques, papules or nodules. There are no ulcers or additional symptoms.

Diagnosis

For the diagnosis of the disease, the detection and identification of amastigote is necessary. This requires obtaining a skin sample by scraping or aspirating the lesion. The sample must then be stained with Giemsa's stain to show and identify amastigote.

Cultures should be performed in NNN media for at least 4 weeks, as growth can be slow. The identification technique of the isolated species can be monoclonal antibodies, isoenzyme analysis, hybridization with DNA probes, or polymerase chain reaction.

Serology is not recommended as it is not a sensitive test in these cases.

Treatments

There is no specific optimal treatment for the disease. Localized cutaneous leishmaniasis tends to heal spontaneously after several months and leaves scars. Treatment in this case helps to improve healing and prevent the spread of the parasite as well as relapses of the disease.

Traditional treatment consists of the use of antimonials such as sodium stibogluconate or meglumine antimoniate, administered intramuscularly or intralesionally. These drugs can have serious but reversible side effects, such as kidney failure, muscle pain, and liver or heart toxicity.

Recent treatment alternatives are amphotericin B, pentamidine, mitelophysin, paromomycin, thermotherapy, and also chemotherapy.

Prevention

Suggested preventive measures to avoid the disease include:

Attempt to reduce the size of vector populations by using insecticide spraying.

Treat insect screens, mosquito nets, clothing, and sheets with repellants with diethyltoluamide (DEET), permethrin, or pyrethrin.

References

1. Mexican Leishmania. On Wikipedia. Recovered from: wikipedia.org.
2. RD Pearson (2017) Leishmaniasis. In MSD Manual. Professional version. Recovered from: msdmanuals.com.
3. IL Mauricio (2018). Leishmania taxonomy. In F. Bruschi & L. Gradoni. The Leishmaniases: old neglected tropical disease. Springer, Cham.
4. Leishmania. On Wikipedia. Recovered from: en.wikipedia.org.
5. Leishmaniasis. Recovered from: curateplus.marca.com.
6. T. del R. Rabes, F. Baquero-Artigao, MJ García (2010). Cutaneous leishmaniasis. Pediatrics Primary Care.