infectious diseases: vector-borne/parasitic diseases

definiton

any living creature that transmits an infectious agent to humans

• often used to refer to insects and arachnids (ticks) that are vectors

vectors & diseases the cause

• mosquitos —> malaria, zika virus

• ticks —> lyme disease

  • big problem in TX

• fleas —> plague

  • there are still some cases in NM

• Triatomine bugs —> Chagas disease

vector-borne diseases

• major vector-borne diseases together account for >17% of all infectious diseases

• vector-borne disease burden is highest in tropical & subtropical areas

• affect low-income populations the most

  • low awareness

  • $ is a big factor

  • housing isn’t good

    • hole in the screen, gap in the wall

transmission - mosquito

uninfected mosquito bites infected human —> mosquito picks up pathogen and is now a disease vector —> mosquito bites a person who is not infected —> mosquito transmits the pathogen to the person and infects them

reservoirs

organisms or inanimate objects containing viable disease organisms

vectors

organisms that actively transmit the disease organism

mosquito-borne diseases

• malaria (protozoan parasite)

• dengue virus

• zika virus

• west nile virus (problem is brazos valley)

• chikungunya virus

• yellow fever virus

mosquito behavior

• where they live, what time of day/night do they bite, whether they prefer blood of humans vs. non-humans

• changes in mosquito ranges due to climate change

• travel to unfamiliar places

• excess water = mosquito breeding ground

• occupations that require extensive outdoor work

  • if you’re gonna travel, tell the Dr. and ask what you need to do

zika virus & microcephaly

• if someone gets it during pregnancy, the baby can get it

• spread by infected Aedes aegypti and Aedes albopictus mosquitoes

• these mosquitoes bite during the day and night

• these mosquitoes are found throughout the US

• zika can be sexually transmitted

• zika virus infection of the mother during pregnancy can cause microcephaly in the baby

dengue

• mosquito-borne, viral disease

• 4 closely related dengue viruses (DENV-1, -2, -3, -4)

• 2019: listed by WHO as one of the world’s top 10 public health threats

• symptoms can be mild or severe

  • severe = typically after fever begins to drop, warning signs of severe dengue can appear

    • bleeding from nose or gums (hemorrhaging), vomiting blood, blood in stool, extreme tiredness, belly pain

rocky mountain spotted fever

• tick-borne disease

• caused by bacterium Rickettsia rickettsii

• symptoms include fever, headache, rash

• the disease can rapidly progress to a serious and life-threatening illness

• start doxycycline before definite diagnosis - median time to death is 8 days

• doesn’t result in chronic or persistent infection, but may cause amputation of arms, legs, fingers or toes, hearing loss, paralysis, or mental disability

lyme disease

• tick-borne disease (blacklegged ticks; Western blacklegged ticks)

• caused by the bacterium Borrelia burgdorferi

• most cases can be treated successfully w/ antibiotics

• don’t jump or fly

• questing: grab onto whatever animal comes by

• prevention:

  • insect repellent

  • removing ticks promptly

  • reducing tick habitat

  • applying pesticides

lyme diseasse symptoms

• typical symptoms include fever, headache, fatigue, skin rash

• if left untreated: can cause sever arthritis, or neurological or cardiac problems

preventing tick-borne diseases

• know where ticks live & avoid them

• treat gear, clothing (NOT bare skin) w/ 0.5% permethrin (pesticide)

• use DEET (repellant)

• pets: tick prevention product from vet

• indoors:

  • check clothing, body, pets for ticks

  • looks for nymphs (smallest size)

  • examine clothing, gear, pets

  • shower soon after being outdoors

    • high heat will kill them

neglected tropical diseases (NTDs)

• diseases that predominantly lower-income populations face; cause substantial morbidity & mortality

• all low-income countries are affected by multiple NTDs

  • ongoing chronic disabilities (blindness)

• social stigma & disability

  • lost income

  • children kept out of school

  • reduced ability to care for family

• people in the US are also affected

• parasitic worms and protozoan parasites cause a number of important NTDs

• malaria isn’t one

Schistosomiasis (Schisto, Bilharzia, Snail Fever) (NTD)

• causes a lot of illness & death

• caused by parasitic worms of genus Schistosoma

• transmission: infection through skin contact w/ the water

• symptoms include:

  • blood in urine or stool

  • anemia

    • parasite takes some of the nutrients for itself

  • problems w/ growth & development in children

  • bladder cancer

  • kidney & liver damage

  • makes the stomach puff up

• of parasitic diseases, impact of schistosomiasis is second only to malaria

• most deadly NTD; kills approx. 280,000 individuals/yr only in Africa

hookworm - Necator americanus (NTD)

• approx. 570-740 million people infected

• transmission: primarily by skin contact w/ soil contaminated w/ hookworm larvae (walking barefoot; can penetrate the skin of humans)

• itching and localized rash

• can cause fatigue, abdominal pain. diarrhea, loss of appetite, weight loss, anemia

• severe infections can impact the cognitive/physical growth

protozoans

• microscopic, one-celled organisms

• can be free-living or parasitic

• four groups based on type of movement:

  • amoebas - entamoeba

  • flagellates leishmania

  • ciliates - balantidium

  • organisms whose adult stage is not motile - plasmodium

• there’s a variety of them w/ diff characteristics

malaria

• mosquito-borne disease caused by 4 species of the protozoan parasite plasmodium; the most severe form is caused by P. falciparum

• transmitted by:

  • bite of female anopheles mosquitoes (bite dusk to dawn)

    • insecticide treated bed nets

  • in utero

  • blood transfusions

  • organ transplant

  • sharing needles (IV drug use)

malaria vaccine

• the malaria parasite has multiple different developmental stages and effective ways of avoiding immune response

• vaccines targeted at a single antigen or a single life stage of the plasmodium parasite have not been very effective

• multi-antigen, multistage vaccines (elicit different kinds of immune responses directed toward different antigens) - more promising

malaria symptoms

• fever

• flu-like illness

• chills

• headache

• muscle aches

• nausea

• vomiting

• diarrhea

• anemia

• jaundice

  • indicated that liver is failing

• can progress to kidney failure, seizures, coma, death

malaria exposure

• exposure to malaria parasites does not provide lifelong protection against future disease; people can still become infected

• importance of temp: at temp below 68%°F (20°C) - plasmodium falciparum can’t complete growth cycle

chagas disease (NTD in TX)

• also called american trypanosomiasis

• vector borne transmission by triatomine bug (or “kissing bug”); caused by the protozoan parasite trypanosoma cruzi

• chagas disease in TX

  • 2013-2016: 91 cases in TX, 20 acquired in TX

  • many may be unaware they are infected

• you don’t get symptoms right away

  • they can be lingering

• protazoan found in feces

• found in chickencoops

chagas transmission

• like to live in nooks & crannies

• contact w/ the feces of an infected triatomine bug (kissing bug)

• contaminated blood transfusion/organ transplant

• mother-to-baby transmission

acute phase - chagas

• can last a few months

  • may cause fever of swelling around site of inoculation; occasionally causes severe inflammation of heart muscle or brain and lining around brain

• next, prolonged asymptomatic phase w/ few /no parasites in blood

• an estimated 20-30% of infected individuals develop debilitating, potentially sever effects:

  • heart rhythm abnormalities that can be fatal

  • other cardiac alterations

  • dilated esophagus or colon, causing functional problems w/ eating/elimination

giardia lamblia

• many people get it when they’re out camping

• waterborne protozoan pathogen

• transmission:

  • ingestion of contaminated food or water (drinking or recreational water)

  • ingestion of pathogen from hands/fomites

• causes gi distress

• not effectively eliminated from water by iodine or chlorination

• killed in water by rolling boil for 1 min (higher altitudes use 3 min) or special filtration

• in USA in 2019: 14,887 reported cases (96.6% confirmed & 3.4% nonconfirmed)