Vectorborne diseases
Selected Insect-borne diseases
Since vectorborne disease include both insects (especially mosquitoes) and arachnids (ticks and mites), it is more appropriate to collectively refer to these diseases as arthropod borne diseases (sometimes abbreviated as arbo -- for example, an arbovirus is an arthropod borne virus). Among the true insectborne diseases, we begin this section with a disease spread by the blackfly, and then survey the wide range of mosquito borne diseases.
1. Onchocerciasis (river blindness)
agent: Onchocerca volvulus (nematode, or roundworm)
reservoir: mostly humans
transmission: bite of infected female blackfly
(genus Similium) biological vector
symptoms: chronic, nonfatal (incubation 1 year or more)
intense itching, impaired vision
A. mosquito-borne
2. human malarias
agent: a parasitic protozoan in the Plasmodium genus
reservoir: mostly humans and infected mosquitoes
transmission: Anopheles mosquites
symptoms: fever, chills, sweats
CNS effects (headache, delirium, coma)
3. filariasis
agent: Wuchereria or Brugia genus (nematodes, or roundworms)
reservoir: humans
transmission: mosquitoes (Aedes, Anopheles, or Culex)
(The mosquito carries the microscopic larval stage
of the worm)
symptoms: asymptomatic; fever, asthma
elephantiasis in chronic cases (enlarged limbs)
4. yellow fever: one of the few immunizations required for
travel in endemic areas
agent: yellow fever virus (a flavivirus)
reservoir: humans (sometimes monkeys) and mosquitoes
transmission: Aedes mosquito
symptoms: sudden onset of fever, jaundice,
headache, backache, vomiting, diarrhea
5. dengue fever (also called breakbone fever)
agent: Dengue virus
reservoir: human, infected mosquitoes
transmission: Aedes mosquitoes
symptoms: headache, joint and muscle pain, rash
with low case fatality rate
6. Arthropod-born viral encephalitis
agents: Eastern equine encephalitis, Western equine encephalitis,
California encephalitis, West Nile virus, etc.
reservoir: unknown for most agents
(possibly birds, rodents, bats, reptiles)
found in more temperate areas (e.g., North America)
transmission: Culex mosquitoes, possibly Aedes and others
symptoms: often asymptomatic
inflammation of brain, spinal cord, meninges
headache, fever, convulsions, paralysis, coma
Selected Arachnid-borne diseases
A. Tick-borne
1. Rocky mountain spotted fever (tickborne typhus fever)
agent: Rickettsia rickettsii
reservoir: dogs, rodents, other animals
transmission: bite of infected ticks (various species)
tick must be attached 4-6 hours
symptoms: maculopapular rash (bumpy spots on the skin)
fever, headache, malaise, chills, rash, death
2. Tularemia: discovered in Tulare County, California
agent: Francisella tularensis (related to plague bacteria)
reservoir: wild animals (rabbits, muskrats, squirrels);
this disease is mostly a disease of animals,
and is sometimes known as "rabbit fever"
transmission: bite of deer flies or wood ticks,
handling or ingestion of infected animals
symptoms: typically: swollen lymph nodes, gastroenteritis
untreated, it can be fatal
3. Colorado tick fever
agent: Colorado tick fever virus (an arbovirus)
reservoir: small animals (squirrels, chipmunks, porcupine)
transmission: infected ticks: Dermacentor andersoni
symptoms: similar to Dengue fever (joint and muscle pain; headache, fever, rash)
4. Q fever (first found in Queensland, Australia)
agent: Coxiella burneti (a rickettsia)
reservoir: ticks, various wild and domestic animals
transmission: raw milk from infected cows, or direct contact with infected animals
symptoms: typically: chills, headache; low case fatality
5. Relapsing fever
agent: Borrelia recurrentis (a spirochete)
reservoir: from lice: human; from ticks: rodents
transmission: lice or ticks
symptoms: gets its name from a fever that disappears and
reappears, rash also
6. Lyme disease discovered in 1975 in Lyme, Connecticut, it appeared
as a cluster of arthritis cases in children as well as adults
agent: Borrelia burgdorferi (discovered by Wally Burgdorfer)
this agent is a spirochete
reservoir: nymphs and adult ticks are found on white tailed deer
larval ticks are found on white footed mice
transmission: deer ticks (Ixodes genus)
symptoms: it starts with a blemish that resembles a blood blister in a "bulls-eye" pattern;
it then develops into flu-like symptoms, later into arthritis;
advanced cases can include heart disease and various neurological effects;
it is curable at all stages with antibiotics, but the joint degenerations that
is associated with the arthritis may be irreversible.
controls: control the ticks!
stay on trails when hiking; use repellants; stay covered whenever possible;
inspect for ticks frequently;
remove ticks using a tweezer on the mouth parts with a steady pull
(easier said than done!)
B. Mite-borne
7. Scrub typhus (also known as mite-borne typhus)
agent: Rickettsia tsutsugamushi
reservoir: infected larval mites (chiggers), wild rodents
transmission: mite bites
symptoms: skin ulcer at site of bite, maculopapular rash,
headache
8. Scabies (sarcoptic itch, acariases)
agent: Sarcoptes scabiei (a mite)
reservoir: humans
transmission: skin to skin, clothing, bedding;
mites can burrow into skin in < 3 minutes
symptoms: itching, lesions
there are various drugs for treating mites,
but they are always more effective with thorough daily bathing,
and laundering of all clothing and bedding
1. Zoonoses: diseases and infections transmitted between
vertebrate animals and humans
2. Plague:
agent: Yersinia pestis
reservoir: wild rodents (especially squirrels)
transmission: Bubonic plague is spread by flea bite
(especially Xenopsylla cheopis, the Oriental rat flea)
These fleas can spread from rats to pets (dogs and cats)
Pneumonic plague is spread person to person
(respiratory route)
symptoms: swollen lymph nodes (buboes), fever, pneumonia
the pneumonic form is particularly virulent
3. Murine typhus fever (also called endemic typhus or flea-borne typhus):
agent: mainly Rickettsia typhi
reservoir: rodents, fleas,
transmission: bite or feces of Oriental rat flea (Xenopsylla cheopis)
symptoms: headache, chills, fever with low case fatality rate
4. Leptospirosis:
agent: Leptospira interrogans (a spirochete)
reservoir: farm animals and pets;
usually rats and other rodents
transmission: contact of skin with water, soil or vegetation
contaminated by rodent urine!
symptoms: may be asymptomatic,
fever, headache, chills, malaise, vomiting
5. Psittacosis: found worldwide but very often unrecognized
sometimes called parrot fever (psittacos = parrot)
agent: Chlamydia psittaci
reservoir: birds (pigeons, parrots, parakeets,
turkeys, ducks)
transmission: airborne (inhaling dried droppings)
person to person is rare
incubation 4-15 days (usually about 10 days)
symptoms: varies (fever, headache, chills, sometimes cough)
6. Rabies:
agent: rabies virus
reservoir: 1. skunks 2. bats and racoons
3. foxes 4. dogs, cats, cattle
squirrels are rarely infected with rabies
transmission: mainly animal bites, or licks on wounds
rarely: scratches, airborne, person to person
symptoms: untreated, almost always fatal
fever,
neurological: paralysis, inflamation of the brain
spasms in throat, leading to "hydrophobia" (fear of water),
resulting in foaming at the mouth typical in rabid animals
and the appearance of choking
controls: vaccinate pets and high-risk humans (e.g., veterinarians)
keep your distance from wild animals that appear to be choking!
(sadly, well meaning animal-lovers have ended up with rabies)
if you are bitten by a wild animal, retain the animal's head, if possible, for testing
if pets are bitten, re-vaccinate
if pets are unvaccinated, pets must often be destroyed
however, it's possible to detain the pet for 6 months and,
if there are no behavioral changes, the animal can be released
6. Hantavirus: hantavirus made big news in the 1990's because of its high case fatality
in young healthy people in the U.S., and because the treatment options are limited.
The key is rodent control!
agent: hantavirus
reservoir: deer mice (but not urban rodents)
transmission: inhaling airborne virus from mice droppings
symptoms: flu-like symptoms; breathing difficulties; related to the hemorrhagic fevers
controls: control the mice:
open windows to ventilate closed areas
do not vacuum or sweep (instead, use a wet mop)
use mouse traps and other mice controls
Test your knowledge with a: quiz
For more information, try: pests and pesticides
Back to HOME PAGE