African trypanosomiasis

Question 1

Describe the disease progression (i.e. time taken for disease) of HAT

Answer 1

Can be variable- with progression taking from a few weeks to a few years (rhodesiense vs gambiense respectively). First, there is an early stage followed by a late-stage where the parasite spreads to the brain and causes the “sleeping sickness”.

Question 2

Describe the outcome of HAT if not treated

Answer 2

Invariably fatal.

Question 3

When were the epidemics of HAT?

Answer 3

40s, 90s, again in 2004. With each subsequent epidemic, numbers reported of HAT went down, despite actually increasing in the 90s but this was followed by a subsequent decline that correlated to interventions.

Question 4

Which factors may lead to an increase in cases of HAT?

Answer 4

• Destruction of infrastructure (e.g. due to war)

- Decrease in surveillance

Question 5

How many cases would we like to have be 2020 in order to consider HAT eliminated? (How many cases, what global incidence?). How would this be maintained?

Answer 5

<1 case per 100,000 in 90% of endemic areas. Also a global incidence of <2000 cases. Maintained by surveillance.

Question 6

Describe the host range of the HAT vector?

Answer 6

Promiscuous host range of vector. Bites lots of hooved species as well as domestic and wild mammals.

Question 7

How big is the tsetse fly? how does it feed?

Answer 7

6-8mm long. Feeds on a pool of blood it creates.

Question 8

What are the habitats for palpalis and morsitans tsetses?

Answer 8

Rivers and savannahs respectively. Both in low lying vegetation.

Question 9

Describe the distribution of tsetse flies and HAT? Describe livestock in this area.

Answer 9

Highly correlated- tsetse belt. There is low animal husbandry in this area as infection is rife.

Question 10

Which parasite causes HAT?

Answer 10

T brucei.

Question 11

Describe the location of t brucei parasites in hosts.

Answer 11

Obligate extracellular in both human and vector. In the blood and lymph of humans as well as having an affinity for the skin and adipose tissue.

Question 12

How does t brucei aviod the immune response

Answer 12

Avoids the adaptive immune response through antigenic variation. Does this by swapping its coat every couple of generations.

VSG is the variable surface glycoprotein

Question 13

Describe the mitochondria in t brucei

Answer 13

One single MT stretches the entire length of the cell

Question 14

What is the kinetoplastid? How is the kinetoplastid in brucei and cruzi different?

Answer 14

A huge amount of circular DNA (a ridiculously complex mitochondrial genome). Is mainly introns and must be processed. Brucei has a small kinetoplastid whereas cruzi has a large one.

Question 15

Where does energy production occur in trypanosomes (brucei and cruzi)?

Answer 15

In the gycosome. Glycolysis is compartmentalised and does NOT occur in the cytoplasm.

Question 16

How are trypanosomes motile? What is the directionality?

Answer 16

Using their flagella. Move in the direction of the flagella (forwards). Flagellum comes from the flagellar pocket. Can swim directionally or tumble.

Question 17

Describe what happens from when t brucei is injected into the skin.

Answer 17

Enters the lymph and blood as the long slender form. Bacterial like quorum sensing tells them to differentiate into the short stumpy form, ready for life in insect

Question 18

What is the purpose of the short stumpy form of t brucei?

Answer 18

It is a form stuck in G0 and is adapted to live in the insect.

Question 19

What gives the plasma membrane of t brucei its shape?

Answer 19

The subpellicular microtubule cytoskeleton.

Question 20

What is the reason for the waves of parasitemia?

Answer 20

As previous VSG expressing variants are cleared by the immune system, new switched variants emerge (sequential expression and clearance of VSG variants).

Question 21

Describe the long term memory and clearance by the immune system

Answer 21

No long term memory and never gets cleared by the immune system effectively as the antigenic switching allows it to outrun the immune system.

Question 22

Why are the MT upregulated in the stumpy form?

Answer 22

Because it is mainly amino acids (lots of proline) in the insect. In the human blood, there is a lot of sugar so therefore MT are DOWN regulated because it doesn’t need to use the Kreb’s cycle so much and mainly uses glycolysis (does not require the MT).

Question 23

What does the stumpy form differentiate to once inside the insect?

Answer 23

Differentiates from the G0 undividing stumpy form to the dividing procyclic form.

Question 24

Which is the definitive host for t brucei and why?

Answer 24

The tsetse fly.

Because genetic exchange (sexual stage) occurs inside the tsetse fly.

Question 25

Surra is an AAT caused by which species?

Answer 25

T. brucei evansi

Question 26

Why is AAT as important as HAT?

Answer 26

Food availability has an impact on public health.

Question 27

Which tb species differs to T.b. brucei by only one gene?

Answer 27

T. brucei equiperdum

Question 28

Which two tb species have evolved to NOT need tsetse flies? How are these both spread instead and how has not needing tsetse flies impacted their distribution?

Answer 28

Evansi and equiperdum. Evansi spread by biting flies and equiperdum is venereal. Both now have a more wide spread incidence.

Question 29

Where and why is T.b. vivax spreading? How is it spread?

Answer 29

Is spreading to S america due to animal export. It does not require tsetse and is spread by biting flies and vampire bats.

Question 30

Describe the spread of gambiense and rhodesiense trypanosomiasis.

Answer 30

Gambiense is in west and central Africa (despite its name, the Gambia has not had a case for decades). Rhodesiense has a more focal (small no of foci), often found in game reserves.

Question 31

What happens when AAT enters the human bloodstream?

Answer 31

The vacuole distends in human serum and is lysed.

Question 32

How does the human immune response cause the lysis of non-human trypanosomes?

Answer 32

TLF1 and TLF2 complex delivers ApoL1 to the parasite. A low pH causes it to insert into the membrane and form pores, causing ion flux and subsequent lysis.

Question 33

Which african trypanosome subspecies cause AAT? Which two cause HAT?

Answer 33

HAT: gambiense and rhodesiense

AAT: Tb brucei (ss), tb evansi, eb equiperdum, t vivax, t congolense.

Question 34

How have rhodesiense and gambiense evolved to avoid lysis by apoL1?

Answer 34

Rhodesiense:
Expresses truncated VSG and SRA (serum resistance associated protein) binds to Apol1 very tightly and prevents it integrating into the lysosomal membrane i.e. blocking it in the endosome.

Gambiense:
Has a three pronged (multifactoral) approach:
-Modifies receptor so it can no longer take up TLF as effectively.
-Truncated another VSG which integrates into memrbane where it thinks ApoL1 is likely to be (therefore not directly interacting with ApoL1) and makes the membranes less amenable to Apol1 integration.
-More proteolytic lysosome so because of the above point, apol1 gets integrated into the membrane slower so more is exposed to the highly proteolytic environment.

Question 35

Where are the early and late stages?

Answer 35

Early: Lymph blood and skin.

Late: Encephalytic.

Question 36

What occurs at the site of the bite with gambiense and rhodesiense that may allow identification among the few specific symptoms that arise that may allow diagnosis?

Answer 36

Rhodesiense: chancre at bite.

Gambiense: winterbottom’s sign (enlarged gland in neck).

Question 37

What is the usual time periods for the early stages of rhodesiense and gambiense?

Answer 37

Rhodesiense is much more rapid onset (a few weeks) whereas gambiense may take years.

Question 38

Why is blood smear microscopy not always the best to diagnose t brucei?

Answer 38

Gambiense has low parasitemia in the blood (rarely seen in the blood). However, rhodesiense has very high parasitemia.

Question 39

How is HAT diagnosed?

Answer 39

• Blood microscopy
• Blood concentration techniques
• Lumbar puncture to look at CFS
• WBC used as a surrogate marker (as we don’t always see the parasite in the blood).
• CATT test (indirect serology)

Question 40

What is the problem with looking at CSF to diagnose trypanosoma?

Answer 40

Requires a lumbar puncture. May introduce early stage parasites into the CSF and induce late stage disease.

Question 41

Descrive how a CATT test can be used to diagnose HAT? What are the advantages and disadvantages?

Answer 41

Card agglutination test. Mix blood and antigen on a card. Gives blue granular deposits if positive.
Disadvantages:
-Result can be ambiguous
-Can only be used with gambiense as it is based on a particular antigenic type (that most gambiense express).

Advantages:

• Cheap
• Easy to do
• Can screen large population quickly

Question 42

What are the 4 drugs used in chemotherpy against HAT?

What are the problems with these current drugs?

Answer 42

• Suramine
• Pentamidine
• Melarsoprol
• Eflournithine

Problems:

• Subspecies specific
• can cause a huge antigenic burst (reactive encephalopathy)
• Cross resistance is emerging.

Question 43

What is the new drug that has just come out in 2018? Why is it so good?

Answer 43

Fexinidazole.

Only requires one dose, is very effective and is effective against early AND late stages of gambiense.

Question 44

Which is the one country where both gHAT and rHAT are found? Why might we see this overlap?

Why is this overlap a problem?

Answer 44

Both found in Uganda.

• Migration of people
• Cattle may be carrying rHAT (may be multiplicity of infection in cattle).

Is a problem because usually in diagnosis, we assume (based on the geographical location/ distribution of each g/rHAT) which one it is, in areas of overlap we can no longer do this so we must diagnose more carefully and hence treatment is more complicated (as we must diagnose first).