Parasitism

Ecological niche

multidimensional summary of a species’ tolerances and requirements

Fundamental niche

niche occupied without interspecific competition

Realised niche

niche occupied in the presence of competition

Competitive exclusion

one species eliminated when niches overlap extensively

Resource partitioning

coexistence through division of resources

Symbiosis

intimate co-evolved relationship between species

Parasitism

parasite benefits at the expense of the host

Parasite reproductive potential

greater than that of the host

Host specificity

parasites often restricted to specific hosts

Degenerate parasites

loss of structures due to reliance on host

Ectoparasites

parasites living on host surface

Endoparasites

parasites living within host tissues

Single-host lifecycle

parasite completes lifecycle in one host

Multiple-host lifecycle

parasite requires more than one host

Definitive host

host where parasite reaches sexual maturity

Intermediate host

host required for lifecycle completion

Vector

organism transmitting parasite and sometimes acting as host

Malaria

disease caused by Plasmodium

Plasmodium in humans

asexual reproduction in liver and red blood cells

Plasmodium in mosquitoes

sexual reproduction following gametocyte ingestion

Schistosomiasis

disease caused by schistosome parasites

Schistosome lifecycle

sexual reproduction in humans and asexual reproduction in snails

Viruses

obligate intracellular parasites

Viral genetic material

DNA or RNA enclosed in protein coat

Viral envelope

phospholipid membrane derived from host cells

Viral antigens

molecules on virus surface recognised by host

Viral replication

host enzymes replicate viral genome and proteins

Retroviruses

RNA viruses using reverse transcriptase

Transmission

spread of parasite to host

Virulence

degree of harm caused to host

Ectoparasite transmission

direct contact or ingestion of intermediate hosts

Endoparasite transmission

often vector-mediated

Transmission factors

overcrowding vectors and waterborne stages

Extended phenotype

parasite-induced changes in host behaviour

Immune suppression

parasite reduction of host immune responses

Non-specific defences

physical chemical and cellular responses

Physical barriers

skin and epithelial tissues

Chemical defences

enzymes and low pH secretions

Inflammatory response

increased blood flow and immune cell recruitment

Phagocytosis

engulfment and digestion of parasites

Natural killer cells

induce apoptosis in infected cells

Cytokines

signalling molecules attracting immune cells

Lymphocytes

white blood cells with specific antigen receptors

Clonal selection

antigen binding triggers lymphocyte division

Antibodies

proteins with variable regions binding antigens

Primary response

initial immune response forming memory cells

Secondary response

faster stronger and longer-lasting response

Immune evasion

parasite strategies to avoid immune detection

Antigenic variation

switching surface antigens

Viral latency

integration into host genome

Epidemiology

study of disease spread

Herd immunity threshold

proportion resistant preventing epidemics

Vaccines

antigens stimulating immune responses

Parasite control difficulty

similarity of parasite and host metabolism

Control challenges

overcrowding tropical climates and poor sanitation

Public health measures

sanitation engineering and vector control

Development impact

parasite control improves child development and intelligence