Infectious Diseases lesson 9

Infectious Diseases

• Clostridium botulinum - Botulism:
  • Gram-positive, large, blunt-ended rods that produce endospores.
  • Most species are motile obligate anaerobes.
  • Found in soil and aquatic sediments; its spores contaminate vegetables, meat, and fish.
  • Causes botulism (food poisoning) and floppy baby syndrome.
  • Colonizes the large intestine, producing exotoxin slowly absorbed.
  • Inhibits acetylcholine release at neuromuscular junctions, causing flaccid paralysis, vomiting, and diarrhea.
  • Symptoms include lethargy and poor muscle tone; death can occur due to respiratory paralysis.
  • Treatment: Horse anti-serum (antitoxin) administered as soon as possible.
  • Prevention: Proper food preservation techniques to prevent clostridial exotoxin production; avoid swollen or dented canned food, especially homemade.

Clostridium tetani & Tetanus

• Pathogen: Clostridium tetani, a common soil bacterium.
• Morphology: Vegetative cells are gram-positive rod-shaped.
• Infectious agents: Spores infecting puncture wounds, severe burns, or postsurgical incisions; fecal contamination of umbilical cord (neonatal tetanus).
• Mechanism: C. tetani exotoxin (tetanospasmin) binds irreversibly to neurons, blocking neurotransmitter release at inhibitory synapses.
• Action: Tetanus toxin travels retrograde from the peripheral nervous system to the central nervous system.
• Mechanism Cont.: Prevents presynaptic release of inhibitory neurotransmitters glycine and GABA.
• Outcome: Causes severe, prolonged muscle spasms (spastic paralysis).
• Clinical presentations:
  • Early stages affect jaw muscles (trismus or lockjaw), preventing mouth opening.
  • Other voluntary muscles gradually become involved.
  • Death often results from chest muscle paralysis, leading to respiratory failure.
  • Clinical presentation (Cont):
    • Patients have prolonged muscle spasms of both flexor and extensor muscles.
    • Spastic muscle contractions, difficulty opening the jaw (trismus), characterized by a smile ("risus sardonicus"), and back muscle contractions with backward arching (Opisthotonos position).
    • Patients are extremely irritable and susceptible to seizures.

Entamoeba histolytica - Amoebic dysentery

• Defining pathogenic species: Entamoeba histolytica.
• Stages: Immotile, highly resistant cysts and trophozoites (actively feeding and reproductive stages).
• Pathogenesis (Read): Trophozoites invade large intestinal walls, multiply in submucosa and form flask-shaped ulcers, ingesting blood cells from damaged capillaries.
• Subsequent complications: Amoebic liver abscess can form when trophozoites are carried to the liver via portal circulation, forming abscesses typically in the right lobe in adults and more often in males.
• Transmission: Fecal-oral route (alimentary).
• Infective stage: Mature cysts.
• Localisation: Large intestine.
• Pathogenesis (Cont): Ingested cysts form trophozoites in the small intestines, moving to the colon, infecting normal intestinal flora, resulting in ulcers in the intestinal wall leading to acute or chronic diarrhea, including blood and mucus in stools.
• Extra-intestinal amoebiasis: Abscesses in the liver, lungs, brain, or skin.

Leishmania Mexicana - Cutaneous leishmaniasis

• Pathogen: Leishmania mexicana, Leishmania tropica, and Leishmania braziliensis.
• Classification: Subphylum Mastigophora (flagellates).
• Disease: Cutaneous leishmaniasis (local).
• Geographic distribution: Central and South America, Africa, and parts of Asia and Europe.
• In Belize: Found in northern and southern Belize, especially in densely forested areas where loggers, soldiers, and forestry department personnel reside.
• Transmission: Sand fly vector ( Phlebotomus or Lutzomyia genera).
• Hosts: Humans, dogs, and wild rodents.
• Localisation: Cells of the skin.
• Further notes: Promastigotes (with flagellum) develop in the intestine of the sand fly.

Trypanosoma cruzi – Chagas disease

• Pathogen: Trypanosoma cruzi.
• Disease: American trypanosomiasis, or Chagas disease.
• Geographical distribution: South and Central America.
• Vector: Infected bug species of the family Triatomidae (Reduviid bugs, nocturnal).
• Other transmission modes: Congenital transmission or blood transfusion.
• Reservoir hosts: Armadillos, opossums, rodents, monkeys, dogs, and cats.
• Localisation: Blood (acute phase), cells of lymph nodes, spleen, liver, brain, and muscles.
• Acute presentation: (usually asymptomatic), but may present with fever, rash, headache, lymphadenopathy, and edema of the brain (Romaña sign-swollen eyes).
• Chronic presentation: Alternating periods of fever and apparent recovery, followed by depression, lethargy, potentially leading to heart (cardiomegaly, dilated cardiomyopathy) and/or esophagus complications.
• Diagnosis: Serological methods to detect the presence of antibodies; xenodiagnosis using "clean" laboratory-bred triatomine bugs.

Explore the crucial aspects of two significant infectious diseases caused by Clostridium botulinum and Clostridium tetani. Understand their characteristics, symptoms, treatment options, and prevention methods. Test your knowledge on how these pathogens affect health and safety.