Transcript Piroplasms

Apicoplast
 Apicomplexa maintain a chloroplast-like organelle
 This organelle is the product of an ancient secondary
endosymbiosis event (eukaryote ate cyanobacterium producing
algae/plants, other eukaryote ate alga)
 The apicoplast is home to essential biochemical pathways (fatty
acids, isoprene and heme) and these are of bacterial origin
 Drugs targeting the apicoplast are already in use and more are
hopefully to be developed
 Domestication of an endosymbiont involves gene transfer to the
nucleus and the establishment of mechanisms to import the
proteins encoded by these genes back into the organelle
Piroplasms: Babesia &
Theileria
Piroplasms
Piroplasms or Piroplasmida are an order
of the Apicomplexa
They are very small parasites of mammals
and ticks
There are two genera which cause import
disease in livestock (and occasionally in
humans): Babesia & Theileria
Devastating outbreaks
follow the big cattle drives
 In the 1860s and 1870s Texas longhorns
were driven in huge numbers to the
railheads in Kansas (from there they
went by train to the slaughterhouses of
Chicago and other big nothern cities)
 Farmers in Kansas and Missouri were
plagued by outbreaks of “Texas” fever in
their herds which they linked to the
cattle drives
 Several standoffs ensued as local
farmers tried to block drives
 Theobald Smith and Frederick Kilbourne
show (1889-1893) that the disease is
caused by a protozoan parasite
transmitted by ticks (first disease shown
to be transmitted by an arthropode)
Babesia bigemina causes
Texas cattle fever
B. bigemina
• Mortality in acute untreated cattle
50-90%
• Rapid rise in temperature (105-108
F)
• Fever persists for a week or more
• Loss of appetite, dull, listless
• Severe anemia due to rapid loss of
red blood cells
• Hemoglobinuria (red colored urine)
due to massive RBC lysis
• Infected RBCs adhere to
vasculature of organs (likely similar
in mechanisms to Plasmodium)
• Evidence for comparable clonal
antigenic variation
• Cattle may die within 3-8 days
Babesia bigemina causes
Texas cattle fever
• Older cattle is much more likely
to develop severe disease than
calves
• In endemic areas calves get
infected and mortality is low
• In the case of epidemics adults
without previous exposure get
infected resulting in massive
loss
• This explains the massive loss
of cattle in Kansas despite the
fact that the longhorns coming
from Texas (where the disease
was endemic) seemed perfectly
healthy
• What makes the difference
between Texas & Kansas?
Distribution of Tick fever
caused by B. bigemina
Babesiosis coincides with the distribution of the main
vector ticks Boophilus annulatus & microplus (Winter
temperatures limit distribution)
Babesia
 Merozoites (piroplasms) multiply
in RBCs of the mamalian host
 Tick takes up sexual stages with
blood meal, gamete formation,
fertilization
 Kinetes infect various organs of
the tick including ovary
(transovarial infection of next
generation of ticks)
 In the larvae the kinetes invade
salivary gland cells, massive
replication results in the
production of ten thousands of
sporozoites which are injected
upon feeding
Boophilus is a single host
tick
 In the U.S. & Mexico Babesia
bigemina is transmitted by
Boophilus annulatus
 Boophilus are one host ticks:
larvae hatch from the eggs on
the ground and attach to a
host
 Ticks stay on host and feed
and molt several times until
they are adults
 Engorged and fertilized
female drops of to lay eggs
and dies
 Transovarial infection is very
important for effective
transmission in one host ticks
Disease control is mostly
through vector control
 Disease can be treated with drugs
 A partially effective attenuated
vaccine is available
 Tick control mostly through pesticide
application remains the most
important counter measure
Vaccination of cows with an
antigen from the tick midgut
Antigen Bm86
gut
Host
Salivary gland
normal
vaccinated
 Proteins found on the
surface of the gut
epithelium of Boophilus
ticks have be
characterized and used
to make a recombinant
vaccine (against the
tick not the parasite)
 Ticks fed on vaccinated
cows are exposed to
antibody/complement
mediated attack of their
epithelium
 These tick grow poorly
and have low fecundity
Border Cowboys patrol the
U.S. Mexican border for ticks
Eddie Dillard, left, and Jack Gilpin
are tick riders (NYT 7/03)
 Boophilus ticks and with
them the Texas tick fever
have been eradicated from
the Southern U.S. but they
are still present in Central
America
 USDA employs 60 cowboys
which patrol the Southern
border to find and check
stray-cattle for ticks to
prevent the reintroduction
 See short New York Times
feature on border cowboys
posted on the class web site
Infrequent human babesiosis
in the U.S. by B. microti
 Some species of Babesia
(in particular B. microti) that
naturally infect small
rodents like the whitefooted mouse can also
infect humans
 B. microti is transmited by
infected Ixodes ticks (dear
ticks)
 Most transmission occurs
along the North-Eastern
seaboard and infection
rates can be relatively high
locally
 The epidemiological risk
factors are very similar to
Lyme disease
Infrequent human babesiosis
in the U.S. by B. microti
Human blood film with B. microti, Giemsa stain
Vannier & Krause 2009
http://www.hindawi.com/journals/ipid/2009/984568.html
 Many infections likely go undiagnosed,
about a third of the infections are
asymptomatic
 Most infected show mild disease with
general malaise and fatigue and fever
and chills
 People who are elderly or immunecompromised (including in particular
people without a spleen) are most
likely to show severe disease
 Heavy RBC infection in severe cases
can lead to acute respiratory failure,
congestive heart failure and other
complications with a mortality rate of 510%
 Babesiosis can be treated with
antibiotics that target the apicoplast
and/or the parasite mitochondrion
Theileria
Life cycle and transmission of Theileria
Host cell invasion by Theileria -- what
are the differences to Toxoplasma
East coast fever and tropical
theileriosis
Theileria manipulates its host cells
Theileria
cattle: disease
Cape buffalo: reservoir
 Infects mainly
ruminants (cattle,
goats, sheep)
 Several different
species causing both
pathogenic and
benign disease
 Infection in wild
animals is mostly
asymptomatic
Distribution of theileriosis
red = T. annulata
orange = T. parva
grey = T. buffeli/orientalis/sergenti
250 million cattle at risk
50 million cattle at risk
relatively benign
Life cycle of Theileria spec.
 Life cycle in tick similar to that
of Babesia
 However, no transovarial
transmission (vectors are multihost ticks)
 Two different cell types are
infected in the mammalian
blood stream (initially
leukocytes later on RBCs)
 Infection of RBCs is important
for transmission and infection
of lymphocytes is important for
pathology
 T. parva (mostly T-cells), T.
annulata (B-cells,
macrophages)
Two stages are found in the bovine
host: Koch’s bodies and piroplasms
 Koch’s bodies, infected
lymphocytes
 Piroplasms, infected red
blood cells
Theileria (sporozoite) invasion
differs from Toxoplasma invasion
Theileria invasion
 Zipper mechanism of
entry into lymphocyte
 Escape from vacuole
into cytoplas
coincides with
rhopthry &
microneme discharge
 Parasites free in the
cytoplasm associate
with host MT
Animated version
The Theileria paradox
 Although Theileria replicates in lymphocytes these cells
seem to proliferate enormously in infected animals (most
of these proliferating lymphocytes are infected) -- this is
in contrast to other infections like malaria or babesiosis
where parasite replication is associated with the decline
of the host cell population causing anemia
 Also, the sporozoite (injected by the tick) appears to be
the only stage capable of invading lymphocytes
 How can the parasite spread to new lymphocytes?
 The trick: Theileria hijacks and exploits two key features
of the lymphocyte’s cell biology: cell division and growth
control
Divide & conquer
Divide & conquer
 Parasites do not egress from (and
in the process destroy) their host
cells and infect new lymphocytes
but proliferate along with them
 The tight association of parasites
with host cell microtubules
ensures that they are segregated
by the host cell mitotic spindle
between the two daughter cells
 A recently divided infected
lymphocyte (the arrow indicates
the cleavage furrow at which
cytokinesis occurred. Blue (DNA),
red (host cell centrioles), green
(parasite surface membrane), HN
(host nucleus)
Theileriosis is a lymphoproliferative disease
 Recall the immunology
lecture -- lymphocytes are
usually arrested and only
expand upon antigen
presentation
 If parasite replication
requires host cell replication
the parasite has to somehow
induce proliferation of its
host cells
 Indeed theileriosis is a
lympho-proliferative disease
 Swelling and proliferation of
the lymph node draining the
bite site is the first sign of
disease
Pathology is mainly due to
lymphoproliferation
 Lymphocytes proliferate heavily
invading multiple organs
causing disease similar to a
lymphoma (cancer of
lymphocytes)
 (Top) Infiltration of kidney by
Theileria parva infected
lymphocytes
 (Bottom) Abdominal ulcers due
to transformed lymphocytes
 Death is in most cases due to
infiltration of the lung resulting
in lung edema (the abnormal
build up of fluid within the lung)
Theileria infected cells show
characteristics of transformation
 Theileria infection seems to share
many of the features seen in the
transformation of normal cells into
cancer cells
 Uncontrolled growth
 Loss of differentiation
 Immortalization (infected cells taken
into culture will grow indefinitely)
 Growth in the absence of external
growth factors
 Enhanced ability to migrate and to
infiltrate organs
 When cells are cured from parasite
infection they die (by apoptosis -- this
suicide response is usually
suppressed in cancer cells)
How does Theileria interfere
with lymphocyte growth and
cause cancer?
NF-kB -- a major regulator of
lymphocyte growth
 NFkB (nuclear factor, p50 & p65) is an
important and very well studied
transcription factor (a protein that
interacts with the promoter of genes and
stimulates gene expression)
 It is a major player in the stimulation and
clonal expansion of lymphcytes
 NFkB is bound by IkB (its inhibitor) which
retains it in the cytoplasm and keeps it
inactive
 Phosphorylation followed by
ubiquitinylation and degradation of IkB
leads to import into the nucleus and
transcriptional activity
 Theileria interferes with this pathway by
causing the destruction of IkB
The IKK complex
 IkB is tagged for
destruction by
phosphorylation through
the IKK complex
 In the lymphocytes this
provides a way to relay the
reception of signals from
the surface of the cell to
gene expression
 Theileria hijacks and
activates the IKK signaling
complex independent of the
usually required external
stimulation
Hijacking and activation of IKK
transforms infected cells
 Theileria parasites (green) interact with and activate
IKK (red) of their host lymphocytes
 IKK tags IkB for destruction
 NfKb free of its inhibitor enters the nucleus and cells
start dividing rapidly
summary
 Theileria sporozoites invade using a zippering
mechanism
 The PV is lysed upon rhoptry secretion and the
parasites resides in the cytoplasm and associates with
the host cell’s microtubuli & centrosomes
 When the host cell divides the parasite divides and
segregates alongside using the host cell’s mitotic
machinery
 Theileria schizonts transform their hosts lyphocytes
(induce uncontrolled ‘cancer-like’ growth)
 Transformation is parasite dependent and reversible
 Parasites interfere with NFkB growth control by
activating the IKK signalling pathway