Vector borne diseases

Question 1

what are the four main types of vector borne disese

Answer 1

1) Arboviruses = arthropod borne viruses e.g. dengue, marbug and japanese encephalitis

2) bacterial diseases = Rickettsia (typhus), Yersina (bubonic plauqe)

3) protozoan parasites = trypanosoma, leishmania, plasmodium

4) metazoan parasites = microfilarial nematodes

Question 2

outline characteristics of the metazoan parasite filarial nematodes and what its vector is

Answer 2

adults 6-10cm long
coiled tightly in lymph glands and ducts of humans
females release microfilariae

VECTOR= mosquitos and several species

Question 3

outline characteristics of w.bancrofti, a microfilariae in the blood and who its vector is

Answer 3

270 x 8.5 um
sheath around its body to help prevent host immune response recognition
no nuclei in the tip of the tail

VECTOR = culex, Manzonian, Anopheles, Ades

Question 4

outline the characteristics of the microfilariae found in the blood which causes river blindness

Answer 4

onchocerca volvulus

320 x 7.5 um
adults live in fibrous nodules in subcutaneous connective tissues
no sheath
no nuclei in tip of tail
larvae invade the eye causing cataracts

VECTOR = simulium species, blackflies that breed in rivers

Question 5

what is meant by microfilarial periodicity

Answer 5

Hawkings 1960’s

found microfilariae are not always present in the blood
during the day they migrate into viserca to avoid host immune responce from macrophages in blood before migrating back at night

back at night due to vector ecology ( mosquito is nocturnal) so higher chance of being spread

Question 6

outline some characteristics of the protozoan parasite the Kinetoplstida

Answer 6

• possess a kinetoplast
  = disc like structure that stains like a nucleus as it has DNA inside
  = found close to flagellum
• different stages during its lifecycle
  1) trypomastigote
  2)amastigote
  3) promastigote
  4) amastigote

Question 7

outline the activity of the leishmania species from the kinetoplastida in its vector the sandfly

Answer 7

metamorphose into promastigote form
multiplies and blocks the foregut as it is relatively larger than vector
ingested into human when vector takes blood meal

Question 8

outline the activity of the leishmania species from the kinetoplastida in a human host

Answer 8

promastigote form is phagocytosed by macrophages turning into amastigote form
lives within host macrophages
taken up by sand fly vector during blood meal

Question 9

what are the two types of groups in the trypanosoma species from kinetoplasts

Answer 9

1) Stercorarian (transmission by contamination
2) salivarian (transmission by inoculation via insect mouth parts)

Question 10

name the vector which transmit stercorarian individuals from trypanosoma species from kineotplasts and its life stages

Answer 10

triatome bugs
associated with poor living conditions and made up of 15 genera
- eggs layed in human habitations
- nymphs hatch in 7-30 days, similar to males but dont possess wings
- undergo 5 nymphal instars each of which need a blood meal
- adult form after 3 months - 2 years

feeding behaviour = nocturnal and often on the host face

Question 11

how can trypanosoma species be controlled

Answer 11

1) Treat the host = Nifurtimox or Benznidazole (toxic)

2) control the vector = residual insecticides such as DDT or pyrethroids, habitat management and alteration ( hard to do in practise cause of money

Question 12

give some examples of species which are vector borne diseases from trypanosoma species in the salivarian group

Answer 12

1) t.b. brucei
2) t.b. gambinese
3) T.b rhodesinese

vectors = dipteran flies e.g. tsetse fly

Question 13

outline tsetse fly morphology (vector of salivarian trypanosoma species)

Answer 13

at rest their wings are closed unlike normal flies whose wings are open

defined hatchet cells made up of 4-5 veins

very painful bite

Question 14

outline the tsetse fly biology

Answer 14

) Female fly inseminated by male; sperm stored in
spermathecae

b) Female takes blood meal: single egg passes from
ovary to uterus

c) Egg fertilised by sperm from stored spermathecae

d) Larvae hatches from egg in uterus

e) Larvae receives nutrient from uterine milk glands; after 4 – 5 days it reaches 3rd instar
(adult fly takes regular blood meals)

f) After 10 days, larvae is 8 – 9 mm long and weighs as much as adult female.
Larvae is deposited in shady site, under bushes

g) Larvae burrows into soil, pupates for 4 – 5 weeks

h) Adult fly emerges from puparium; forces its way up through ground

9 – day period of post-emergence development (cuticle hardens, thoracic flight muscles
increase in size)

j) Females live for 100 – 200 days: produce 5 – 8 offspring

Question 15

outline how tsetse flies feed

Answer 15

hypopharynx and pointed labrum thrust into the skin

saliva, containing anticoagulants, pumped down the phyopharynx

blood flows up channel

= both males and females take blood mean so both vectors of trypanosomes

Question 16

outline the route taken by trypanosomes when tsetse flies take a blood meal

Answer 16

from the midgut
2) pass through the peitrophic membrane
3) into the ectoperitrophic space
4) migrate into the proventriculus
5) invade salivary glands as epimastigotes

= takes 18-35 days (therefore vector needs to live this long = not efficient)