ZOOL 452 – January 21, 2014
Parasites living on the surface of the host (ectoparasites)
ectoparasites infest their hosts. Not infect them.
• Host finding
o Active or passive finding
o Monogeneans and sea lice smell their host. They are attracted to the host’s
mucus. Some monogeneans can detect the mucus of different kinds of
hosts and can have some host specificity.
o Wood ticks ▯respond to carbon dioxide. CO2 activates the tick larvae and
causes them to move faster.
Shadow from the host also activates the larvae.
Larvae of the ticks travel no more than one metre up the tick. That
is exactly how high they have to go to attach to moose. Positioning
and the recognition of host cues are important.
Wood ticks have to get their blood meals in order to be able to
o Some are transmitted by insects. Some ectoparasites lay eggs on the host.
Larvae hatch and develop in the host’s tissues. Eg: botfly infestations.
o Passive finding ▯depends on the density of the susceptible hosts
Susceptible hosts in aquaculture tanks are close together ▯
transmission is easier. Also, fish that are closer together are more
stressed and are more susceptible to infection.
• Ectoparasites that live in the gills will suffocate the fish
• Establishment in host
o Parasites may have hooklets, specifically designed claws that allow them
to attach to the hair of the host
o Suckerlike structures can also be used for attachment.
o Eg; wood tick have specialized structures for penetration. Create a
cementlike material that allows it to stay on the host while feeding and
stay during host grooming
o Parasites try and select parts of the host’s body that are not groomed very
easily. Very heavy infestations can result from this ▯may lead to death.
This is why some people think that
o Why do ectoparasites in the gills survive better than ectoparasites in the
Gills = super nutrient rich. Parasites can get whatever they want
Gills can’t be rubbed off
o Spatial partitioning on the host’s surface is what happens more often than
o Bulla = attachment structure on sea lice.
o “Ich” = ciliated protozoan parasites that live on the fish. Transmission is
promoted by the crowded conditions in which the commercial fish live. o Whales have skin that makes it difficult for ectoparasites to attach
o Mucus is secreted by fish onto their surface. It is a protective layer that the
ectoparasite has to deal with.
o Hair on hosts help the parasites establish (this applies to ticks, fleas, etc)
o Host specificity
Depends on whether or not a parasite can establish on a host. Some
ticks are highly host specific. This is not well understood.
Rabbit flea is HIGHLY specific to the rabbit host.
• Living on the host
o Terrestrial ectoparasites, when they feed on the host, sensitize the
basophils. Eg: tick saliva stimulates the immune system of the host and
suppresses the immune system by downregulating cytokine production in
o Both male and female ticks feed on blood, but the female tends to get
MUCH bigger. Can be up to 5 cm long when they become super engorged.
Phenomenal change in the organism’s shape
Specialized enzymes that break down the hemoglobin. Allows
nutrients from the blood to be taken into the tick.
o Monogeneans and sea lice feed on the mucus that the fish secrete. Sea lice
in heavy infestations may take up some blood. But, it’s mainly just the
mucus that they feed on
o Mites and fleas ▯feed on blood and skin (also, sebaceous secretions)
o Dame Rothschild showed that the female hormones of the rabbit were
necessary for the rabbit flea’s life cycle’s progression.
Female rabbits provided a susceptible population of young rabbits.