Insect-Borne Diseases

Viruses

• Smallest and simplest disease-causing agent

• A fragment of DNA or RNA wrapped in a protective protein coat

• Not really alive

  • Hard to find drugs that work

  • Tiny “freeloading zombies”

• They have to hijack a host cell to replicate

  • Using our own cells makes treatment challenging

Bacteria

• Larger than viruses

• Living single-celled organisms

• Require food to stay alive

• Can reproduce on their own

• Because they are alive, they can be killed

• Can treat with antibiotics

Protozoa

• Single-celled organisms with a nucleus and other cell structures

• Bigger and more complex than bacteria

• Show characteristics associated with animals

• Some are free-living, but some are parasites that can cause diseases

Worms

• Large, multicellular organisms

• Adults visible to the naked eye

• Can be either free-living or parasitic

• Parasites include:

  • Tapeworms

  • Flukes

  • Roundworms

River Blindness

• Caused by parasitic worm

• Transmitted by black fly infected by worm

• Fly bites a human and drops worm larvae which penetrate skin

• 25 million infected

• 300,000 blind

• 800,000 visually impaired

• 99% of infected are in Africa

• Remainder in Yemen and Americas

• Adult female worm can live 10-15 years and produce millions of new larvae

• Possible Effects

  • Asymptomatic

  • Nodules under skin

  • Itchy skin rash

  • Eye disease

• 2nd leading infectious cause of blindness

• Debilitating and disfiguring skin disease

• Anti-parasitic medication kills worms

Chagas Disease

• Caused by Kissing Bug

• Disease caused by protozoa

• 8-10 million people in Central and South America infected

• Primary Transmission

  • After kissing bug bites, it shits

  • Protozoa are in the feces

  • People scratch the bite: feces and protozoa enter the bloodstream

• Also Possible

  • Mother to fetus

  • Blood transfusion and organ transplant

  • Eating uncooked food contaminated with feces from infected bugs

• Symptoms

  • 2 Phases: both can either be symptom-free or life-threatening

  • Phase 1: Acute

    • Mild fever, fatigue, aches, diarrhea, rash

    • Eyelid swelling is best sign

    • Children may die from heart trouble

  • Phase 2: Chronic Phase

    • Infection may be silent for decades to life

    • Risk of serious complications = 30%

    • Heart Problems: enlarged heart, heart failure, altered heart rhythm, cardiac arrest

    • Digestive Problems: Intestinal complications, enlarged esophagus, difficulty eating

• Treatment

  • Anti-parasitic to kill protozoa in acute phase

  • Symptomatic to manage symptoms

  • Pacemakers for irregular heartbeat

  • No preventative drugs or vaccine

The Black Plague

• Killed about 40% of Europe’s population in the 1300s

• No understanding of disease transmission meant no defense

• Everyone was terrified; the sick were abandoned

• Spread from rodent to rodent by fleas

• Disease caused by bacteria

• Humans can get it from flea bite, direct contact with the sick or dead animal, respiratory droplets from infected cats and humans with plague pneumonia

Bubonic Plague

• Sudden fever, headache, chills

• Swollen, painful lymph nodes

Septicemic

• Infection in blood

• Fevers, chills, weakness, abdominal pain, shock, bleeding into skin and organs

• How it got the name Black Death

Pneumonic Plague

• In lungs

• If untreated, 1st 2 kinds can progress to this

• Fever, headache, weakness, rapidly-developing pneumonia, may cause respiratory failure

• Most serious

• Only form with person-to-person transmission

Spread of Plague

• 1st in 1900

  • 80% of US cases: bubonic form

  • Recent decades: 1-17 human cases/yr in US, 1000-2000 cases worldwide

• Treatment

  • Antibiotics given ASAP, preferably within 1st hrs of 1st symptoms

• Death Rate

  • Pre-antibiotics: 66% mortality

  • 1990-2010: 11% mortality so can still be fatal despite effective antibiotics

Houseflies

• “Filth flies'“

• Visit dumps, sewers, garbage, feces, moist decaying matter

• Spread disease since feed on both human food and filthy matter

Housefly Transmitted Diseases

• Suspected of transmitting at least 65 diseases

• Intestinal Illness: Dysentery, Salmonella, Diarrhea, Cholera, E. coli

• Skin Infections: Leprosy

• Eye infections

Body Lice

• Epidemic Typhus

• Caused by bacteria in feces

  • Rub into bite or inhale dried feces

• Treat with antibiotics

• Caused millions of death in previous centuries

• Now considered a rare disease

• In eastern US, occasional cases reported from people exposed to flying squirrels and/or their nests