Insect vectors Dr. Carmen E. Rexach Micro 1 Mt SAC Biology Department Internet version
Biological vs mechanical transmission Mechanical Pathogen is picked up from a source and deposited on another location Ex) houseflies Biological Natural route of pathogen from host to host Pathogen develops in vector Ex) Female anopheles mosquito and malaria
Biological vectors Mosquitoes Ticks Fleas Lice Flies Bugs
Mosquito vectors
Mosquito vectors Anopheles spp malaria Aedes aegypti Yellow fever Culex tarsalis West Nile virus
Mosquito life stages (Anopheles) Each mosquito has 4 life stages Eggs Larvae Pupae Adults Aquatic stages
Eggs Female mosquitoes lay 50-200 eggs per oviposition directly on the water Eggs have their own floats on the side They usually hatch within 2-3 days, but could take up to 3 weeks dependent on weather
Larvae Eggs develop into larvae that have no legs, but a large head. They do not have siphon tubes, unlike most mosquitoes. They breathe through spiracles in their abdomen and feed on bacteria and algae on surface of water.
Larvae Larvae have 4 stages of development, called instars, and molt at the end of each stage Anopheles larvae prefer clean, unpolluted water Different species have been found in rice fields, ditches, streams, rivers, rain pools, both shady and sunlit pools, and some in tree holes
Pupae Pupae are comma shaped and must surface often to breathe through respiratory trumpets in the cephalothorax Only remains in this stage for a few days, then cephalothorax splits and adult emerges
Adults 3 sections: head, thorax, abdomen Segmented antennae used to detect odors Mate shortly after emerging as adults Males live for about a week, females for about a month Females 1-2 weeks in nature, dependent on temperature, humidity, and ability to obtain blood meal Proboscis for feeding Male feeds exclusively on nectar Female feeds on nectar, but takes a blood meal before laying eggs Blood used as a source of protein for egg production
Anopheles mosquito and malaria
Mosquito invasive stages
Global distribution of malaria vectors
Ticks
Ticks Soft (Agrasid) or hard-bodied (Ixodid) blood sucking ectoparasites of vertebrae Attach to the host via a hypostome with backward hooking teeth
Ticks Ornithodoros moubata Relapsing fever Ixodes scapularis Lyme Disease Human granulocytic erlichiosis Dermacentor andersoni Rocky Mountain spotted fever
Ornithodoros moubata Soft-bodied tick Feeds for 20-25 minutes, usually at night 4 nymphal stages in male, 5 in female Agent: Borrelia duttoni
Dermacentor andersoni and RMSF Hard-bodied tick Common name: Dog or wood tick Immature stages on rodents, mature stages on man and dog Must remain attached to host for several days to transmit disease Agent: Rickettsia rickettsi
fleas
Fleas Order Siphonoptera Wingless ectoparasites of mammals and birds Laterally flattened 1-6mm long Recurved spines Produce 2-6 eggs per day, develop in 4-6 days dependent on temperature Ex) Xenopsylla cheopis Plague
Xenopsylla cheopis
Flies
Flies Simulian black fly Onchocerciasis Glossina (tsetse fly) African trypanosomiasis
Simulium black fly Must breed in swiftly running water 150-600 eggs laid in water Larva hatch and spin silk web as anchor Constructs cocoon and becomes pupa Female is haemphagous Blood meal takes 4-5 minutes, associated with maturation of ovaries
Glossina Medium to large brown flies 6-14 mm long Female produces fully grown larvae Larvae pupate, then develop into adults Male and female haemophagus Diurnally active, feed outdoors Spend most of their time resting Only 5-15 minutes flying per day
Bugs
Bugs Reduviid bug Triatoma infestans and Chagas disease
Triatoma infestans Life span: 8-16 months Females lay average of 100 eggs 5 instars 6 appendages, two used like arms Yellow/orange with black markings Male larger than female Antennae contain heat sensors for locating prey Wings insufficient to fly but can glide up to 100 meters
Triatoma infestans Nocturnal, photosensitive blood suckers Often bite on face Anesthetic and anticoagulant in proboscis Remove 300mg blood in 30 minutes Defecate while feeding T. infestans vectors Chagas in Bolivia Agent: Trypanosoma cruzi
Lice
Lice Pediculus humanus humanus Epidemic typhus Trench fever Epidemic relapsing fever
Pediculus humanus humanus 6-legs, 2.3-3.6 mm long Live in clothing, bedding Haemophagus, move to skin to feed Crowded conditions, poor hygiene Life stages (25 day lifespan) Nits (6-8/2days: 1 week development) Nymph (10 days to develop: haemophagus) Adult (9-10 days)
Epidemic typhus Transferred by close interpersonal contact Crawl from person to person Move to new host if inc temp or death Eggs hatch only between 23-38oC Infestation causes hardened, deeply pigmented skin (Vagabond s disease)