TRYPANOSOMES AND AFRICAN SLEEPING SICKNESS

Question 1

WHAT IS TRYPANOSOMA BRUCEI AND HOW IS IT TRANSMITTED?

Answer 1

• A UNICELLULAR AND EXTRACELLULAR EUKARYOTIC PARASITES

- TRANSMITTED VIA TSETSE FLIES

Question 2

WHICH DISEASE DOES TRYPANOSOMA BRUCEI CAUSE IN HUMANS AND WHICH IN ANIMALS? WHAT ARE THE CONSEQUENCES?

Answer 2

HUMANS: SLEEPING SICKNESS (FATAL DISEASE, NO VACCINE, TREATMENS CAN BE HIGHLY TOXIC)

ANIMALS, MOSTLY WILD ANIMALS AND CATTLE: NAGANA (MAJOR CONTRIBUTOR TO POVERTY, ECONOMIC IMPACT OF 4.5 BIL $ PER YEAR IN AFRICA)

Question 3

HOW MANY CASES OF AFRICAN SLEEPING SICKNESS ARE THERE EACH YEAR?

Answer 3

CCA 1000

Question 4

OTHER NAME FOR AFRICAN SLEEPING SICKNESS?

Answer 4

• HUMAN AFRICAN TRYPANOSOMIASIS (HAT)

Question 5

WHERE DOES AFRICAN SLEEPING SICKNESS (HAT) OCCUR?

Answer 5

• IN THE 36 SUB SAHARAN COUNTRIES WHERE THERE ARE TSETSE (SPREAD HIGHLY RELATED TO THE PRESENCE OF THE FLY; VECTOR DEFINES THE DISEASE DISTRIBUTION)

Question 6

WHICH PEOPLE ARE MOST EXPOSED TO TSETSE FLIES?

Answer 6

PEOPLE LIVING IN RURAL POPULATIONS DEPENDENT ON AGRICULTURE, FISHING, ANIMAL HUSBANDRY OR HUNTING

Question 7

WHAT ARE THE ‘FOCI’ OF INFECTION?

Answer 7

the places where the key elements necessary for transmission of a disease are present: vectors and reservoirs

Question 8

WHICH COUNTRY IS THE MAJOR DISEASE FOCI FOR AFRICAN SLEEPING SICKNESS?

Answer 8

DEMOCRATIC REPUBLIC OF THE CONGO

Question 9

HOW MANY SUB SPECIES OF AFRICAN TRYPANOSOME CAUSING HAT ARE THERE? WHAT ARE THEY AND HOW PREVALENT ARE THEY?

Answer 9

T.B. RHODESIENSE (SEVERE, <10% OF THE CASES)
T.B.B. GAMBIENSE (VHRONIC, 90% OF THE CASES)
—-> HAVE DISTINCT GEOGRAPHIC PROFILES, T.B.G. MORE CENTRAL AND WESTER AREAS, T.B.R. MOR EASTER AREAS

Question 10

ANIMAL TRYPANOSOMIASIS? NAMA+MEANING

Answer 10

IN CATTLE, THE DISEASE IS CALLED NAGANA, WHICH IS A ZULU WORD MEANING ‘TO BE DEPRESSED’

Question 11

IMPACT OF NAGANA (ANIMAL TRYPANOSOMIASIS) ON THE ANIMALS AND THE ECONOMY?

Answer 11

• IN ANIMALS, CAUSES LETHARGY, MASSIVE WEIGHT LOSS AND LOSS OF PRODUCTIVITY
• MAJOR OBSTACLE FOR ECONOMIC DEVELOPMENT OF THE AFFECTED RURAL AREAS
• DOMESTIC AND WILD ANIMALS ARE AN IMPORTANT PARASITE ‘RESERVOIR’ FOR HUMAN INFECTIVE PARASITES

Question 12

EPIDEMIOLOGY OF AFRICAN SLEEPING SICKNESS IN THE HISTORY?

Answer 12

• EPIDEMIC 1896-1906, KILLING 300,000-500,000 PEOPLE (MOSTLY UGANDA AND CONGO)
• EPIDEMIC IN 1920
• DISEASE ALMOST WIPED OUT IN THE 1960s, BUT RELAXING CONTROL MEASURES CAUSED A RESURGENCE IN THE 1970s

Question 13

CONTROL STRATEGIES FOR AFRICAN SLEEPING SICKNESS?

Answer 13

TARGET PARASITE RESERVOIR IN THE HOST: SCREENING AND TREATMENT PROGRAMS FOR HUMANS, TREATMENT OF DOMESTIC CATTLE, ELIMINATING THE WILD ANIMAL RESERVOIR, BETTER HEALTH OF THE POPULATION

TARGET THE VECTOR: SPRAYING OF INSECTICIDES, INSECTICIDE TREATED FLY TRAPS, INSECTICIDE TREATED BED NETS

Question 14

AFTER RESURGANCE IN SLEEPING SICKNESS IN 1970s, CONTROL PROGRAMS WERE RE-IMPLEMENTED, WHEN?

Answer 14

1990s

Question 15

EXAMPLE OF VECTOR CONTROL FOR AFRICAN SLEEPING SICKNESS - NETS

Answer 15

• BLUE FLY TRAPS; NET THAT HAS A PIECE OF BLUE FABRIC NEXT TO IT, FLIE ATTRACTED TO THE COLOUR, FLY AROUND THE NET AND GET INTO IT
• COST IS CCA250$ PER SQUARE MILE
• MUST BE REPLACED EVERY 5 MONTHS

Question 16

TSETSE FLY BITE: WHAT HAPPENS FIRST IN THE PATHOLOGY OF HAT?

Answer 16

• TRYPANOSOMES MULTIPLY IN THE TISSUE AROUND THE INITIAL BITE SITE
• THIS OFTEN RESULTS IN A CHARACTERISTIC LOCAL INFLAMMATION TERMED ‘TRYPANOSOME CHANCRE’
• MOR COMMON IN EUROPEANS; AFRICAN PATIENTS OFTEN EXHIBIT NO PATHOLOGY AT THIS STAGE

Question 17

PATHOLOGY OF AFRICAN SLEEPING SICKNESS?

Answer 17

1) TRYPANOSOMES MULTIPLY AT THE SITE OF THE BITE, PATCH OF INFLAMMATION FORMS (MORE COMMON IN EUROPEAN THAN AFRICAN PATIENTS)
2) EARLY STAGE=HAEMOLYMPHATIC STAGE: FROM THE INITIAL BITE SITE, PARASITES ENTER THE BLOOD, LYMPHATIC SYSTEM AND BODY TISSUES WHICH CAUSES REGULAR BOUTS OF FEVER AND FLU LIKE SYMPTOMS + MAY CAUSE SWELLING OF THE LYMPH NODES (WINTERBOTTOM’S SIGN) —> SYMPTOMS AT THIS STAGE ARE QUITE MILD IN THE GAMBIENSE SPECIES BUT CAN BE SEVERE IN THE RHODESIENSE WITH OFTEN A FATAL OUTCOME
3) LATE STAGE=ENCEPHALITIC STAGE: TRYPANOSOMES CROSS THE ‘BLOOD-BRAIN’ BARRIER AND ENTER THE CNS LEADING TO SYMPTOMS LIKE ENCEPHALITIS, HEADACHES, SLEEPING DISORDER, ABNORMAL BEHAVIOUR (AGRESSION IRATIONALITY, LEADING TO LOSS OF CONSCIOUSNESS AND COMA
- –> OFTEN FATAL IF UNTREATED
- —> ACUTE FORM LASTS A FEW WEEKS, CHRONIC FROM LASTS MONTHS TO YEARS

Question 18

UNTIL 2010, THE MOST WIDELY USED TREATMENT FOR SLEEPING SICKNESS WAS?

Answer 18

MELARSOPROL, AN ARSENIC DERIVATIVE, THAT KILLED 1 IN 20 PATIENTS

Question 19

HOW MANY STAGES DOES AFRICAN SLEEPING SICKNESS HAVE?

Answer 19

3, AND THE 3RD ONE IS TRYPANOSOMES CROSSING THE BLOOD-BRAIN BARRIER TO KILL THE PATIENT

Question 20

WINTERBOTTOM’S SIGN?

Answer 20

SWELLING IN THE LYMPH NODES ASSOCIATED WITH THE 2ND STAGE OF THE AFRICAN SLEEPING SICKNESS

Question 21

PARASITAEMIA RELATED TO TRYPANOSOMES IS MUCH HIGEHER IN RODENTS OR COWNS AND HUMAN?

Answer 21

RODENTS

Question 22

STUDIES IN 2016 REVEALED THAT WHICH ORGANS ARE MAJOR RESERVOIRS OF TRYPANOSOMES? HOW DID THAT INFLUENCE UNDERSTANDING OF THE DISEASE, HAT?

Answer 22

SKIN (MAKES SENSE BECAUSE THE PATHOGEN IS INTRIDUCED BY THE TSETSE FLY BITING THE SKIN) & ADIPOSE TISSUE
—> BEFORE THAT, PRESENCE OF TRYPANOSOMES IN THE SKIN WAS OVERLOOKED AND HAT WAS CONSIDERED TO BE A ‘HAEMOLYMPHATIC DISESE’

Question 23

ARGUMENTS FOR AND AGAINST ADIPOSE TISSUE BEING A FUNCTIONALLY SIGNIFICANT AREA FOR TRYPANOSOMES TO INHABIT?

Answer 23

FOR:

• TRYPANOSOMES APPEAR TO ADAPT TO THIS NICHE BY UPREGULATING FAT METABOLIC ENZYMES
• MAY EXPLAIN THE WASTING DISEASE PATHOLOGY

AGAINST:

• LARGELY HIDDEN FROM BITING TSETSE
• AFRICAN COWS HAVE LITTLE FAT ANYWAY

Question 24

SOME UNANSWERED QUESTIONS ABOUT BLOODSTREAM TRYPANOSOME HABITAT?

Answer 24

• ARE PARASITES IN THE FAT, SKIN AND THE BLOOD FUNCTIONALLY IDENTICAL
• ARE FAT AND SKIN PARASITES ‘PROTECTED’ FROM DRUG TREATMENT
• CAN PARASITES FROM THE FAT, SKIN AND BLOOD REPOPULATE EACH OTHER
• ARE PARASITES FROM THE FAT, SKIN AND BLOOD EQUALLY TRANSMISSIBLE
• ARE PARASITES FROM THE FAT, SKIN AND BLOOD EQUALLY PATHOGENIC (WHICH POPULATION KILLS PEOPLE???)

Question 25

WHAT ARE THE 2 DISTINCT PARASITE STAGES IN THE LIFECYCLE OF THE TRYPANOSOMES?, DESCRIBE THEM

Answer 25

- SLENDER (LONGER AND SLENDER, PROLIFERATIVE, SPECIALISED FOR GLUCOSE METABOLISM VIA GLYCOLYSIS, DIFFERENTIATES INTO STUMPY FORM IN RESPONSE TO SECRETED QUORUM SENSING FACTORS, NON TRANSMISSIBLE) - STUMPY (SHORT AND STUMPY, CELL CYLE ARRESTED; NON-PROLIFERATIVE, PREADAPTED TO SURVIVAL IN THE INSECT MIDGUT (METABOLIC, PROTEASE RESISTANT, EXPRESS SENSORY PROTEIN...)

Question 26

WHICH STAGE OF THE TRYPANOSOMES LIFE CYCLE IS THE PROLIFERATIVE STAGE?

Answer 26

SLENDER STAGE

Question 27

WHICH STAGE OF THE TRYPANOSOMES LIFE CYCLE IS ADAPTED TO SURVIVAL IN THE INSECT MIDGUT? HOW?

Answer 27

- STUMPY STAGE - ADAPTED BECAUSE IT IS: METABOLIC (MITOCHONDRIAL ACTIVATION), PROTEASE RESISTANT, EXPRESSES SENSORY PROTEINS, RAPIDLY DIFFERENTIATES TO THE INSECT PROCYCLIC FORM IN THE MIDGUT

Question 28

LIFE CYCLE OF TRYPANOSOMES IN THE HOST AND IN THE TSETSE FLY?

Answer 28

HOST: 1) SLENDER FORMS PROLIFERATE 2) AT HIGH PARASITAEMIA, THEY DIFFERENTIATE TO STUMPY FORMS (THIS IS 'QUORUM SENSING', AND IS DUE TO SECRETED PARASITE FACTORS 3) THIS LIMITS THE PARASITAEMIA AND PRESERVES THE LIFE OF THE HOST, ENHANCING PARASITE TRANSMISSION 4) STUMPY FORMS ARE THEN TRANSMITTED VIA THE TSETSE BITE - --> PARASITES TRAVERSE THE TSETSE ANATOMY: HAVE TO MOVE FROM THE CROP (WHERE THE BLOOD MEAL IS TAKEN DURING FFEDING) TO THE MIDGUT (WHERE THE DIGESTION OCCURS) THEN TRAVEL TO PROVENTRICULUS (ACTS AS A 3-WAY 'VALVE' BETWEEN THE CROP, MIDGUT AND PROBOSCIS) AND END UP IN THE SALIVA GLANDS - ---> IN THE MIDGUT, THE SLENDER FORMS ARE KILLED BY PROTEASES, STUMPY FORMS DIFFERENTIATE TO PROCYCLIC FORMS - ---> WHEN THE PATHOGEN REACHES SALIVARY GLANDS, IT IS IN THE 'EPIMASTIGOTE' FORM - ----> AFTER REACHING THE SALIVARY GLANDS, EPIMASTIGOTES ADHERE TO THE SALIVARY GLANDS VIA THEIR FLAGELLUM, REPRODUCE AND DIFFERENTIATE TO METACYCLIC CELLS - -----> METACYCLICS ARE PREADAPTED FOR SURVIVAL IN THE HOST AND GET INJECTED BACK INTO THE HOST WHEN THE TSETSE BITES * WHEN TSETSE BITE AN INFECTED HOSTS, TRYPANOSOMES ARE TAKEN INTO THE INSECT MIDGUT AND TRAVEL TO THE SALIVARY GLANDS AGAIN AND THE CYCLE CONTINUES

Question 29

4 MAIN FORMS O TRYPANOSOMES?

Answer 29

1) SLENDER (PROLIFERATIVE IN THE HOST, E.G. HUMANS) 2) STUMPY (NON-PROLIFERATIVE, TRANSMISSIBLE FORM THAT IS PREADAPTED FOR TSETSE) 3) PROCYCLIC (ESTABLISHES TSETSE MIDGUT INFECTION) 4) METACYCLIC (NON-PROLIFERATIVE FORM THAT DEVELOPS IN INSECT SALIVARY GLANDS THAT INOCULATE A NEW HOST)

Question 30

WHICH FORM ARE TRYPANOSOMES IN WHEN THEY REACH THE TSETSE SALIVARY GLANDS? WHICH STRUCTURE DO THEY USE TO ADHERE TO THE GLANDS?

Answer 30

EPIMASTIGOTE FORM, USE FLAGELLUM

Question 31

WHICH AREAS/ORGANS DO TRYPANOSOMES INHABIT IN THE HOST?

Answer 31

- BLOOD - SKIN - ADIPOSE TISSUE - CNS (ONLY IN LATE, I.E. 3RD, STAGE OF THE DISEASE)

Question 32

TRYPANOSOMES ARE EXTRACELLULAR PARASITES; WHAT DOES THAT MEAN IN REGARDS TO THEIR EXPOSURE TO THE HOST IMMUNE SYSTEM?

Answer 32

- THEY ARE FULLY EXPOSED TO HOST IMMUNE FACTORS, E.G. ANTIBODIES (IMMUNE MOLECULES THAT BIND TO PATHOGENS AND MARK THEM FOR DESTRUCTION BY THE IMMUNE CELLS), COMPLEMENT (IMMUNE MOLECULES THAT 'PUNCTURE' PATHOGENS), IMMUNE CELLS (E.G. MACROPHAGES) - REGARDLESS OF THAT, TRYPANOSOMES ARE ABLE TO SURVIVE IN THE SAME HOST FOR YEARS

Question 33

TRYPANOSOMES VARIANT SURFACE GLYCOPROTEIN (VSG)?

Answer 33

- ONE OF THE KEY CONTRIBUTORS TO TRYPANOSOME IMMUNE RESPONSE EVASION - VSG PROTECTS THE PARASITE CELLS FROM THE HOST IMMUNE SYSTEM BY MAKING A PHYSICAL BARRIER: 1x10^7 DENSLEY PACKED VSG PER CELL (CCA 10% OF TOTAL CELLULAR PROTEIN) ----> PROTECTS THE UNDERLYING PROTEINS FROM ANTIBODY RECOGNITION, PROTECT THE MEMBRANE FROM COMPLEMENTS

Question 34

TRYPANOSOMES HYDRODYNAMIC FLOW?

Answer 34

- ONE OF THE KEY MECHANISMS OF TRYPANOSOME IMMUNE EVASION VSG (ANOTHER FACTOR CONTRIBUTING TO IMMUNO EVSAION) IS HIGHLY IMMUNOGENIC ----> TRYPANOSOMES ESCAPE THE INCOMING ANTIBODIES BY 'EATING' THEM: - AS THE PARASITE SWIMS, THE VSG::ANTIBODY COMPLEX IS 'SWEPT' TO THE POSTERIOR OF THE CELL - THE COMPLEX THEN ENTERS THE FLAGELLAR POCKET (PART OF THE CELL SPECIALISED FOR ENDOCYTOSIS) - THE COMPLEX IS THEN INTERNALISED BY ENDOCYTOSIS AT THAT SITES * IF ANTIBODY LEVELS ARE HIGH, CLEARANCE BECOMES LESS EFFECTIVE AND THE CELL IS LYSED

Question 35

DESCRIBE THE ROLE AND MECHANISM OF TRYPANOSOME IMMUNE EVASION VIA ANTIGENIC VARIATION?

Answer 35

- AFTER ENTERING THE HOST, TRYPANOSOMES ARE IN SLENDER FORM AND THEY PROLIFERATE, REACHING A 'PEAK' AND CHANGING FORM FROM SLENDER TO STUMPY - STUMPY FORM CAN EITER BE TRANSMITTED BY A TSETSE BITE OR CLEARED BY THE IMMUNE SYSTEM - VSG AND HYDRODYNAMIC FLOW ARE STRATEGIES TRYPANOSOMES USED TO ESCAPE THE IMMUNE SYSTEM, BUT VSG IS HIGHLY IMMUNOGENIC AND THE AMOUNT OF ANTIBODIES OFTEN OVERWHELMS HYDRODYNAMIC FLOW KILLING THE CELL, AND THERE IS A LARGE DROP IN OVERALL PARASITEMIA - BUT, AFTER SUCH DROP, THERE IS SOON ANOTHER RISE (SLENDER PROLIFERATION) AND THE CYCLE CONTINUES - THIS IS POSSIBLE BECAUSE OF 'ANTIGENIC VARIATION' - TRYPANOSOMES HAVE 20 DIFFERENT VSG LOCI, I.E. EXPRESSION SITES, LOCATED AT CHROMOSOME TELOMERE, AND EACH SITE CONTAINS A DIFFERENT VSG ISOTYPE - ONLY THE ACTIV EXPRESSION SITE IS EXPRESSED (MONOALLELIC EXPRESION), SO TRYPANOSOMES CAN 'SWITCH' TO A DIFFERENT EXPRESSION SITE CONTAINING A DIFFERENT VSG ISOTYPE FOR WHICH ANTIBODY HASN'T YET BEEN PRODUCED (BUT THIS MIGHT NOT BE A VERY LONG TERM SOUTION) - TRYPANOSOMES HAVE CCA 1000 VSG GENES ELSEWHERE IN THE GENOME (10% OF ALL GENES); LOCATED IN SEVERAL LARGE 'SUB-TELOMERIC ARRAYS' AND NOT EXPRESSED - THESE VSGs CAN BE SWAPPED INTO VSG EXPRESSION SITES BY HOMOLOGOUS RECOMBINATION, WHICH GIVES THEM A REPERTOIRE OF CCA 100 VSGs - SUBTELOMERIC VSGs CAN RECOMBINE WITH THE EXPRESSION SITE VSG, MAKING ENTIRELY NEW VSG 'MOSAICS' -----> LEADS TO UNLIMITED CSG REPERTOIRE - THIS ALLOWS TRYPANOSOMES TO SURVIVE AS EXTRACELLULAR PARASITES FOR YEAR, DESPITE BEING HEAVILY ATTACKED BY THE HOST IMMUNE SYSTEM (EVERYTIME THERE IS A DROP IN PARASITEMIA, NEW VSG IS EXPRESSED AND THE SLENDER PROLIFERATION OCCURS AGAIN)

Question 36

HOW MANY VSG ISOTYPES DO TRYPANOSOMES HAVE? WHY IS THAT USEFUL?

Answer 36

CCA 20 VSG ISOTYPES - ONLY ONE VSG SITE IS EXPRESSED/ACTIVE AT A TIME ('MONOALLELIC EXPRESSION') - AFTER ANTIBODY RESPONSE HAS BEEN PRODUCED BY THE HOST TO ONE SITE, TRYPANOSOMES CAN SWITCH TO ANOTHER VSG ISOTYPE AND CONTINUE EVOLVING - BUT ANTIGENIC VARIATION ALLOWS FOR OTHER UNEXPRESSED VSG GENES IN THE GENOME (THERE IS CCA 1000) TO BECOME EXPRESSED WHEN THE INITIAL ONES ARE EXHAUSTED - ADITIONALLY, THE VSGs CAN MIX LEADING TO MOSAIC VERSIONS OF VSGs AND UNLIMITED REPERTOIRE

Question 37

MAIN TRYPANOSOME IMMUNE EVASION MECHANISMS?

Answer 37

- VSG - HYDRODYNAMIC FLOW - ATIGENIC VARIATION

Question 38

% OF TRYPANOSOME GENES WHICH ARE VSG GENES?

Answer 38

10%

Question 39

WHAT ARE THE 3 WAYS ANTIGENIC VARIATION ALLOWS THE CELL TO CHANGE THE VSG ISOTYPE THAT IS EXPRESSED BY TRYPANOSOMES TO ACHIEVE IMMUNE EVASION?

Answer 39

- EXPRESSION SITE SWITCHING (SWITCHING BETWEEN THE 20 VSG ISOTYPES) - INSERTING DIFFERENT VSG INTO THE EXPRESSION SITE (FROM THE 1000 VSG GENES) - MAKING ENTIRELY NEW, MOSAIC VSGs (UNLIMITED NUMBER OF POSSIBLE COMBINATIONS OF THE 20 ISOTYPES AND REMAINING VSG GENES)

Question 40

THE REASON WHY VACCINE AGAINST TRYPANSOSOMES IS UNLIKELY?

Answer 40

BECAUSE OF ANTIGENIC VARIATION

Question 41

THE 'WAVES OF PARASITAEMIA' IS A CHARACTERISTIC OF WHICH DISEASE/PATHOGEN? WHAT CAUSES THE WAVES?

Answer 41

CHRONIC INFECTION BY TRYPANOSOMES (AFRICAN SLEEPING SICKNESS) WAVES EXPLAINED BY THE FOLLOWING PATTERN IN THE PARASITE'S BIOLOGY: 1) SLENDER FORM PROLIFERATION (RISE) 2) SLENDER TO STUMPY DIFFERENTIATION (PEAK) 3) PARASITE DEATH CAUSED BY ANTI-VSG ANTIBODIES (WHEN HYDRODYNAMIC FLOW IS OVER-WHELMED) (DECLINE) 4) ANTIGEN VARIATION (LEADS TO ANOTHER RISE)