Summary malaria II

Severe forms of malaria include: severe anemia in kids, cerebral and renal malaria in adults, and severe malaria in pregnant women

Severe pathogenesis is related to adherence of infected RBC to entothelia Adherence is mediated by knobs on the RBC surface made up by parasite

proteins (PFEMP1) PFEMP1 undergoes antigenic variation Chloroquine accumulates in the food vacuole and prevents heme

polymerization (detoxification), resistance is linked to mutations in a transport protein in the food vacuole membrane

Emerging drug resistance is a tremendous challenge to the management of malaria, a constant stream of new drugs with novel modes of action is required to stay ahead of the pathogen

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

• 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 mechanism to Plasmodium)

• Evidence for comparable clonal antigenic variation

• Cattle may die within 3-8 days

B. bigemina

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?

Babesiosis coincides with the distribution of the main vector ticks Boophilus annulatus & microplus (Winter temperatures limit distribution)

Distribution of Tick fever caused by B. bigemina

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

Babesia

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

gut

Antigen Bm86

normal vaccinated

Vaccination of cows with an antigen from the tick midgut

Salivary glandHost

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

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

Eddie Dillard, left, and Jack Gilpinare tick riders (NYT 7/03)

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 white-footed 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

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 immune-compromised (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 5-10%

Babesiosis can be treated with antibiotics that target the apicoplast and/or the parasite mitochondrion

Human blood film with B. microti, Giemsa stainVannier & Krause 2009http://www.hindawi.com/journals/ipid/2009/984568.html

Theileria

Life cycle and transmission of TheileriaHost cell invasion by Theileria -- what

are the differences to ToxoplasmaEast coast fever and tropical

theileriosisTheileria manipulates its host cells

cattle: disease

Cape buffalo: reservoir

Theileria

Infects mainly ruminants (cattle, goats, sheep)

Several different species causing both pathogenic and benign disease

Infection in wild animals is mostly asymptomatic

red = T. annulata 250 million cattle at riskorange = T. parva 50 million cattle at riskgrey = T. buffeli/orientalis/sergenti relatively benign

Distribution of theileriosis

Life cycle of Theileria spec.

Life cycle in tick similar to that of Babesia

However, no transovarial transmission (vectors are multi-host 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

Animated version

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

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 lympho-proliferative 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-B -- a major regulator of lymphocyte growth

NFB (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

NFB is bound by IB (its inhibitor) which retains it in the cytoplasm and keeps it inactive

Phosphorylation followed by ubiquitinylation and degradation of IB leads to import into the nucleus and transcriptional activity

Theileria interferes with this pathway by causing the destruction of IkB

The IKK complex

IB 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 NFB growth control by activating

the IKK signalling pathway