Flashcards in Viney Co-infection Deck (14):
is coinfection common?
it is the rule
although not always evident in lab conditions
what is a community co-infection
infection with multiple species
simple example of coinfection in all humans
shown to have profound effects on normal health and
what are two scales of co-infection?
- eg schistosomes and malaria distributions overlap people exposed simultaneously.
2. local scale - in households there is coinfection of schistosomes and malaria.
describe coinfection of schistosomes and malaria
study of Lake Victoria
measured schistosome infection in each household. areas closer to river more infection. Serological measure of plasmodium exposure is similar. each smaller area within this has a different level of co-infection.
what types of interactions can there be between coinfections?
comp for resources
study of sheep coinfection
Haemonchus contortus - blood feeding stomach worm
Trichostrongylus colubriformis - intestinal browsing worm
- cleared sheep of worms
- Groups: 1. control, no infection. 2. T.colubriformis only (1500 per dose)
3. H. contortus only (300 per dose), trickle infections. 4. mixed infection.
- 18 weeks later, intestinal worm counts.
- found that T columbriformis does better when coinfecting, as higher adult count. H contortus has no effect on coinfection or single infection.
Consequence - if sheep treated for H contortus,will have an effect for T columbriformis too. mechanism unknown.
what are some potential mechanisms for the positive effectsof coinfection of T columbriformis and H contortus?
(i) creates or improves the niche for
the other parasite, (ii) induces some immune suppression in the host,
which therefore favours the other parasite. Note, (ii) is a specific
version of (i)
study of coinfection of malaria and Litomosoides sigmodontis
in rat - filarial nematode, adults in thoracic cavity, transmitted by ticks
Groups: 1. uninfected
2. filaria only
3. malaria only
found coinfection leads to more severe disease, anaemia, compared to malaria only mice.
how are coinfections regulated?
Bottom up - limited by resources, eg RBC availability for malaria
Top- down: predator based
what was 3 conclusions of a meta analysis by graham et al 2008
included 54 experiments on mice, of 9 helminths and 29 microparasites
1. parasites causing anaemia provide bottom up regulation of microparasites which require RBC.2. microparasites which dont require RBC have no effect of anaemia inducing worms.
3. coinfection impaired top down control (immune regulation) of microparasites.
more suppression of IFN gamma, = increase in microparasitedensity.
what is the worst case with helminth coinfection?
when helminths do not impose bottom up regulation but remove top down regulation.
what study aimed to see how a hosts microparasite susceptibility is influenced by co infections?
Telfer et al 2010
wild voles: Microtus agrestis
naturally infected with viruses, protozoa and bacteria.
not controlled experiments, inferred coinfections by observation.
studies cowpox, babesia (protozoan) Anaplasma and bartonella (bacteria)
found: widespread, interconnected pos and neg coinfection effects, explaining more variation in infection risk than host age or season.