Leishmania and Its Related Diseases

OTHER Haemoflagellates: Leishmaniasis

• Leishmaniasis is a group of diseases caused by Leishmania parasites.
• The parasites exist in two forms: amastigotes (aflagellar stage) and promastigotes (flagellar stage).
• Four species of Leishmania cause different forms of leishmaniasis.
  • L. tropica causes cutaneous leishmaniasis.
  • L. major causes cutaneous leishmaniasis.
  • L. braziliensis causes mucocutaneous leishmaniasis.
  • L. donovani causes visceral leishmaniasis.
  • L. infantum mainly affects children.
  • L. donovani mainly affects adults.

Leishmania Lifecycle

• The lifecycle involves a sand fly vector and a mammalian host.
• Sand flies ingest infected macrophages containing amastigotes.
• Amastigotes convert to promastigotes in the sand fly's midgut.
• The sand fly injects promastigotes into the mammalian host during a blood meal.
• Promastigotes become amastigotes within macrophages of the host.
• Amastigotes multiply within host tissues and macrophages.
• The cycle continues with new blood meals taken by sand flies.

Leishmaniasis Clinical Types

• Cutaneous Leishmaniasis:

  • Characterized by skin lesions.
  • L. major is a zoonotic form with wet lesions and severe reactions.
  • L. tropica is an anthroponotic form with dry sores and minimal ulceration.

• Visceral Leishmaniasis:

  • Affects internal organs, producing serious complications.

• Mucocutaneous Leishmaniasis:

  • Affects the mucous membranes and skin, often characterized by disfigurement.

• Kala-azar is a term used for a visceral form of the disease seen in India.

Leishmaniasis Pathogenesis

• Fever and malaise (fatigue).
• Weight loss and anaemia.
• Hepatosplenomegaly (enlarged liver and spleen).
• Abdomen protrusion.
• Edema in face, nosebleeds and breathing difficulties.
• Vomiting and diarrhoea.
• Secondary bacterial infections may lead to fatal outcomes.
• Post-kala-azar dermal leishmaniasis (PKDL) can develop after recovery.

Leishmaniasis Diagnosis

• Smear of skin ulcers: Wright's or Giemsa stain microscopy for LD bodies (amastigotes).
• Biopsy: Microscopy for LD bodies or culture in nutritional medium for promastigotes.
• Visceral leishmaniasis diagnosis through:
  • Bone marrow aspirate microscopy and culture.
  • Splenic aspirate microscopy and culture.
  • Lymph node biopsy microscopy and culture.
• Immunological tests: Direct agglutination test (DAT), ELISA, IFAT, skin test (leishmanin test).
• Rapid diagnostics detect malaria antigens.

Leishmaniasis Prevention and Control

• Reduce sand fly populations with insecticides: DDT, dieldrin, malathion.
• Reduce reservoir hosts (e.g., infected animals) with treatment or elimination.
• Educate communities about the causes and transmission of leishmaniasis.
• Prevent exposure to sand flies by using repellents, bed nets, and removing breeding sites.

Malaria: Species, Classification & Lifecycle

• Plasmodium, a parasite, causes malaria.
  • P. falciparum: severe, often fatal malaria.
  • P. vivax: benign tertian malaria.
  • P. ovale: benign tertian malaria.
  • P. malariae: quartan malaria.
• Kingdom: Protista, Subkingdom: Protozoa, Phylum: Apicomplexa, Class: Sporozoa, Order: Eucoccidiida, Family: Plasmodiidae, Genus: Plasmodium.
• Malaria has two hosts: mosquitoes and humans.

Malaria Lifecycle

• Female Anopheles mosquitoes transmit the parasite.
• Sporozoites are injected into the human host.
• Sporozoites invade liver cells, multiply asexually, releasing merozoites.
• Merozoites invade red blood cells and multiply asexually, releasing more merozoites.
• Some merozoites develop into gametocytes.
• An infected mosquito takes a blood meal and ingests gametocytes.
• Sexual reproduction occurs within the mosquito, producing sporozoites that migrate to the salivary glands.
• Sporozoites are transmitted to a new human host.

Malaria: Behavior in Humans

• The parasite avoids the human immune system by moving between hiding places.
• It rapidly travels to the liver (within ~30 minutes).
• The liver cell responds to the presence of the parasite by capturing proteins and displaying antigens for the immune system to see (using MHC).
• The immune response must respond to a constantly changing parasite form to combat its replication.

Malaria: Immune Response

• The immune system recognizes Plasmodium antigens and mounts an immune response.
• However, parasite numbers may quickly increase before a strong response can be made.
• Parasites eventually leave the liver, re-entering the bloodstream to infect red blood cells.

Malaria: Infection of Red Blood Cells

• The parasite uses organelles to enter red blood cells within seconds.
• Plasmodium consumes hemoglobin, breaks it down, and produces waste product (hemozoin)
• Infected red blood cells clump together in capillaries.

Malaria: Cell Rupture & Reproduction

• Red blood cells rupture releasing parasites to infect other red blood cells.
• Some parasites turn into gametocytes.
• Gametocytes are ingested by mosquitoes to complete the cycle.

Malaria: Immune Evasion

• In red blood cells, Plasmodium is hidden from the immune system because red blood cells do not communicate with the immune system.

Malaria: Proteins & Immune Response

• Plasmodium produces many latch proteins via many different genes.
• With each new generation of parasites, some have new proteins, making the immune system continually chase the parasite.
• This makes a strong immune response almost impossible as the protein variation is immense.

Malaria: Paroxysms

• Malaria paroxysms cycle through cold, hot, and sweating stages, with distinct symptoms.

Malaria: Diagnosis

• Blood smears, microscopy, rapid diagnostic testing (detecting malaria antigens) to identify different stages of the parasite in blood films.

Malaria: Prevention and Control

• Early diagnosis and treatment of cases.
• Vector control (e.g. eliminating breeding grounds, insecticide treatment for adult mosquitoes).
• Reducing vector-human contact (using bed nets, repellents, and prevention of standing water).
• Early detection and control of epidemics.

Toxoplasmosis: Overview

• Toxoplasma gondii is an intracellular parasite of many tissues (e.g., intestinal cells and muscles) affecting many animals too.
• It has a complex life cycle, including the need for both a cat (definitive host) and other intermediate hosts (e.g., humans, cattle, sheep, pigs, birds, rodents)

Toxoplasmosis: Lifecycle

• Toxoplasma gondii occurs in different forms through its life cycle: Tachyzoites (rapid-growing stage); Tissue Cysts (Bradyzoites: slow-growing stage); Oocysts (sporulated oocysts: egg stage containing sporozoites).
• Oocysts are released in the cat's feces, developing into a sporulated, infectious stage.
• Other animals become accidentally infected with sporulated oocytes in the environment or contaminated food/water.
• Consumption of infected raw or undercooked meat from infected animals can lead to further infection.

Toxoplasmosis: Human Disease & Congenital Disease

• Acquired Toxoplasmosis: Characterized by painful cervical lymph nodes, fever, headache, sometimes lung complications and even retinal cyst formation, leading to blindness.
• Congenital Toxoplasmosis: Can occur during pregnancy when an infected mother transmits the infection to her fetus, causing lifelong disabilities. Possible outcomes: intracerebral calcification, chorioretinitis (ocular toxoplasmosis), convulsions, mental retardation, and cardiomegaly.

Toxoplasmosis: Diagnosis

• Demonstrate the T. gondii organism in body fluids or tissues.
• Detect T. gondii antigens with ELISA.
• Use PCR to detect the parasite's DNA.

Test your knowledge on the Leishmania species and their associated diseases, including cutaneous and mucocutaneous leishmaniasis. This quiz covers cytokine responses, infectious stages, and diagnostics relevant to leishmaniasis. Challenge yourself and enhance your understanding of these topics in parasitology.