Helminth Vaccines

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It is very difficult to make vaccines against parasites as they are so complex

Gene knockout is useful = potential new drug or vaccine candidate

Challenge - replicate natural immunity by vaccination

ideally = recombinant vaccine (identify single antigen)

Dictol vaccine for lungworm:

D.viviparus highly pathogenic

- infects young calves as most susceptible

Life cycle: PPP 26 days

Eggs hatch in lungs L1 migrate up trachea and swallowed

L1 in faeces

L2

L3 infective stage - ingested and penetrate intestinal mucosa

L4 in mesenteric lymph nodes

Lymphovascular route to lungs

Young adults in bronchioles and small bronchi

Adult worms in mainstem bronchi/trachea

*Eggs hatch in lung - arrest at L3 until taken up on pasture by calfs

good immunity to D.viviparus after infection

but immune response can cause pathology (damage to lung tissue)

immunity boosted by natural challenge

animals have slight cough - low level infection as parasite in lungs

heavy breathing/temperature = heavy infection

Prevention of bovine lungworm:

vaccination with irradiated L3 vaccine (2 doses)

Vaccinate 1st season calves before turnout

oral vaccine

very effective but not sterile immunity (don't mix with unvaccinated)

immunity boosted by infection

Short shelf life and as attenuated it is expensive and have to be administered by a vet

will boost productivity of animals

Larval vaccine is useful - but production is costly and labour intensive

Tapeworm recombinant vaccine (Taenia ovis)

strong immune response

identify antigens recognised that were present on the outside surface (surface Ag of infective stage)

Clone gene for antigen

Express in bacteria

recombinant protein as vaccine - deliver with adjuvant

*Vaccine was a success 95-100% protection

However: expensive

Vaccine for gastro intestinal nematode control:

- focus on antigens extracted from the parasite gut surface - block blood digestion meaning the nematode is unable to survive