Insect Borne Disease

- Diseases discussed will be those transmitted to humans by fleas or ticks
- Weil’s Disease
- Lyme Disease
- Rocky Mountain Spotted Fever
- Plague
1. Weil’s Disease
- Causative agent: Leptospira interrogans. Spiral-shaped, gram-negative spirochete and internal flagella.
- Enters the body via mucous membranes/ breaks in skin
- Localises to the kidneys and liver
- May result in liver or kidney failure
- Can also infect others via infected urine


2. Lyme Disease
- Causative agent: Borrelia burgdorferi. Spiral-shaped, gram-negative spirochete and internal flagella
- Enters the body via tick or louse bite
- Systemic disease develops: Acute headache, backache, chills and fatigue
- If not treated at this stage, can develop chronic disease – numbness of limbs and severe exhaustion
- Little known about pathogenic mechanisms
3. Rocky Mountain Spotted Fever
- Causative agent: Rickettsia rickettsii. Obligate intracellular pathogen and gram-negative bacillus.
- Acquired from faecal matter, injected via bites of ticks or by rubbing infectious material into skin by scratching
- Symptoms:
1. Abrupt onset of fever & severe headache
2. 3-5 days later- rash on hands and feet
3. Diarrhoea and vomiting also usually seen
4. Plague
- Causative agent: Yersinia pestis.Gram negative, Facultative aerobe and Rod-shaped.
- ‘Black Death’
- 14th Century - killed over ¼ population in Europe
- dark skin splodges, lymph node pain, delirium &shock
Virulence factors of Y. pestis:
- V & W antigens – protein/lipoprotein complexes prevent phagocytosis
- Murine toxin (exotoxin) produced by all virulent strains of Y. pestis
- respiratory inhibitor – leads to liver damage, shock and respiratory distress
- Highly immunogenic endotoxin may also be involved in disease process
a. Pneumonic plaque
- Occurs when Y. pestis are either inhaled directly or reaches the lungs during bubonic plague
- Symptoms are usually absent until the last few days when large amounts of bloody sputum are emitted
- Untreated cases usually dead within 2 days
- Highly contagious disease - can spread rapidly via respiratory route if affected are not immediately quarantined.
b. Septicaemia plague
- Involves the rapid spread of Y. pestis throughout the body without the formation of buboes
- Usually causes death before diagnosis can be made


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