Insects – their role in vector-borne diseases.
Insects constitute a very large group of animals and play an important role in the economic life of human beings. Only a small number of insect species act as vectors of human diseases, but these are responsible for the transmission of serious infections such as malaria, typhus and plague, among others.
The insects of special medical importance as parasites include fleas, lice, bugs and flies.
Lice
- Commonly infest:
- Hair of the head
- Body
- Pubic region
- Act as vectors of:
- Epidemic typhus
- Relapsing fever
- Trench fever
Epidemic typhus:
- Occurs in crowded conditions such as:
- Jails
- During famines
- Armies
- Caused by Rickettsia prowazekii
- Lice become infected by ingesting blood from an infected person
- Humans are infected through:
- Louse bites
- Contact of louse feces with wounds
Epidemic relapsing fever:
- Caused by Borrelia recurrentis
Trench fever:
- Caused by Rickettsia quintana
- Commonly seen during World War I
Fleas
- Blood-sucking ectoparasites
- Temporarily infest mammals and birds for feeding
Plague:
- Caused by Yersinia pestis (Gram-negative bacillus)
- Transmitted by fleas from rat to rat
- Human infection occurs via flea bites
- Pulex irritans is an important species
Epidemic (murine) typhus:
- Transmitted from rat to rat and from rat to human
- Caused by Rickettsia typhi
- Organism is excreted in flea feces
Additional roles of fleas:
- May act as mechanical vectors of bacterial and viral diseases
- Transmission often occurs through:
- Contaminated feces
- Wind-borne particles reaching mucous membranes
- Pulex irritans acts as an intermediate host for the dog tapeworm