Human HAT and animal AAT African trypanosomiasis

1
Human (HAT) and animal (AAT) African
trypanosomiasis
Silvia N.J. Moreno Medical Parasitology, CBIO
4500/6500 Spring 2008
2
Human (HAT) and animal (AAT) African
trypanosomiasis
Animal trypanosomiasis causes a negative
economic, social and nutritional impact.
Human trypanosomiasis remains a serious threat
3
Trypanosomes and African trypanosomiasis

• African trypanosomiasis existed for centuries
• Atkins (1742) described a sleepy distemper in
  animals
• 1792, Thomas Winterbottom described negro
  lethargy. Slave shippers rejected those with
  swelling of the posterior cervical lymph nodes
  (Winterbottoms sign).
• David Livingstone (1857) mentioned a fly
  disease
• Griffith Evans (1880) identifies T. evansi as
  agent of surra (horse and camel disease)
• David Bruce in 1894 identifies T. brucei as
  cause of Nagana and demonstrates transmission
  by Tse-tse flies
• First great Epidemic in 1900-killed 1/2 million
  humans around Lake Victoria
• 1902 trypanosomes in human SS by E. Dutton

David Bruce, 1855-1931
Winterbottom sign
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Trypanosomes and African trypanosomiasis
Impact on African History Without
trypanosomiasis the whole of the sub-Saharan
continent would have been readily conquered by
European forces long before the 19th century.
Livingstone was on foot in the middle of the
19th century, horses life span in Africa was
short. Even up to the period of the First World
War. Even Allied forces were losing thousands of
horses to trypanosome infection in East Africa.
Impact on human health and Quality of life At
the turn of the 20th Century farmers in Uganda
were dying in alarming numbers following the
onset of Sleeping Sickness. Deaths reached
300,000. Debilitating disease and death is the
final outcome if not treated. Africans do not
acquire protective immunity to trypanosomiasis,
as they do to malaria. Impact on Agriculture
Nagana has a severe impact on agriculture in
sub-Saharan Africa. The economic losses in cattle
production alone are in the range of US 1.0 -
1.2 billion. A ponderated evaluation extrapolated
for the total tsetse-infested lands values total
losses, in terms of agricultural Gross Domestic
Product, at US 4.75 billion per year.
5
Several species of trypanosomes cause disease in
domestic animals and man
Trypanosoma brucei species Subspecies Trypanosoma
brucei brucei Nagana Trypanosoma brucei
rhodesiense Sleeping sickness (East
Africa) Trypanosoma brucei gambiense Sleeping
sickness (West Africa) Other species T.
congolense Nagana T. vivax Nagana T.
equiperdum Dourine There are trypanosomes
infecting many species of animals and even plants
and every single deer in the State of Georgia
6

• Geographic Distribution of African Trypanosomiasis

HAT is known to occur in rural areas of 36
countries in sub-Saharan Africa. Distribution of
the two sub-species in relation to their presence
in Sub-Saharan Africa. T.b. gambiense is seen in
West and Central Africa and T.b. rhodesiense in
East and Southern Africa.
HAT Human african trypanosomiasis
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Trypanosome transmission
Rhodesiense ungulate-fly-human Gambiense
human-fly-human Brucei game animals-fly-livestock
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T. brucei life cycle
Infection of the mammalian host starts with the
bite of an infected tsetse fly (Glossina spp.),
which injects the metacyclic trypomatigote form
in its saliva (1). The trypanosomes multiply
locally at the site of the bite for a few days
before entering the lymphatic system and the
blood stream (2), through which they reach other
tissues and organs including the central nervous
system (CNS) (3).
Two different trypomastigote forms can be
observed in the mammalian host a long, slender
proliferative form and a short, stumpy
non-dividing form.
Only the short-stumpy forms are able to complete
the complex 2 to 3 week life cycle in the fly.
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T. brucei in the human host
Note that parasites are always extracellular
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T. brucei in the tse tse fly

• Parasites (especially stumpy forms) are taken up
  with the blood meal
• Transformation into procyclics in the midgut
• Migration into the ectoperitrophic space where
  parasites replicate
• Passage into salivary glands, differentiation
  into epimastigotes which attach to the epithelium
  and massively replicate
• Transformation into infectious metacyclic
  trypomastigotes

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Trypanosome biology
Spindle-shaped cell, highly polarized microtubule
cytoskeleton. Highly motile cells. The nucleus
occupies the central region.
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Trypanosome biology
Bloodstream trypomastigotes forms in the
mammalian host Long-slender and short stumpy
Important forms in the life cycle of T.
brucei Trypomastigotes In the mammalian host as
bloodstream trypomastigotes and in the fly as
procyclic trypomastigotes Epimastigote in
the insect vector
Posterior
Anterior
LS
http//www.fao.org/DOCREP/006/X0413E/X0413E06.gif
Experimental Parasitology (2002), 101 (4) p 223
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Trypanosome biology

• Main structures of T. brucei
• Golgi and trans-golgi network
• Subpellicular microtubules
• Glycosomes
• Endocytic pathway
• Nucleus
• Basal body of flagellum
• Surface membrane is densely packed with a
  protein called VSG (variant surface glycoprotein)
• Flagellar pocket
• Flagellum and paraflagellar rod
• Mitochondria
• -kinetoplast

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Sleeping sicknessDisease course and symptoms
Comparison of T.b. gambienseVersus T.b.
rhodesiense infection
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Sleeping sicknessDisease course and symptoms
First stage

• Trypanosomes multiply in the tissue around the
  initial bite site
• This often results in a characteristic local
  inflammation the trypanosomal chancre. Usually
  not painful
• From there they enter the blood and lymphatic
  system

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Sleeping sicknessDisease course and symptoms

• Enlargement of the lymphatic glands (especially
  in the posterior triangle of the neck) can be an
  early sign of the disease (Winterbottom sign, not
  as common in rhodesiense infection).
• Aspiration of swollen gland often reveals
  parasites.

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Sleeping sicknessDisease course and symptoms

• After 1-2 week period of asymptomatic
  incubation, parasites invade blood leading to
  fever and headache
• Once parasites enter blood stream fever sets in
  (low and irregular in gambiense and high and
  periodic in rhodesiense)
• General toxic symptoms include headache, facial
  edema, nausea and vomiting, back and bone pain

T. b. rhodesiense
T. b. gambiense
Symptoms at this stage are rather mild in
gambiense but can be severe in rhodesiense with
often fatal outcome
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Sleeping sicknessDisease course and symptoms

• The second stage of trypanosomiasis is
  characterized by progressive anemia and cachexia.
• Both features are primarily due to extremely high
  serum levels of TNF?
• TNF??was isolated both as factor with tumor
  necrotic effect as well as cachexin inducing
  wasting in nagana

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Sleeping sicknessDisease course and symptomsCNS
involvement

• In later stages of infection parasites pass the
  blood brain barrier and infect the CNS
• Presence of parasites leads to meningo-encephaliti
  s with progressive neurological involvement,
  which ultimately ends in coma (sleeping sickness)
• Untreated trypanosomiasis is always fatal

A young boy with advanced sleeping sickness
exhibiting marked wasting and skin damage caused
as a result of the intense itching which can
accompany late-stage disease.
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Sleeping sicknessDisease course and symptoms

• The progressive encephalitis can cause severe
  dementia with sometimes aggressive behavior
• Disease progression especially CNS invasion is
  much faster in rhodesiense
• Gambiense can take a year or two while
  rhodesiense usually passes the blood brain
  barrier within a month

Neurological complications can occur as a result
of infection and, as seen here, patients may be
immobilized for their own safety. http//www-nt.wh
o.int/tropical_diseases/databases/imagelib.pl?imag
eid9404365
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Sleeping sickness
Neuropathology of Human African Trypanosomiasis
Acute haemorrhagic leucoencephalopathy (AHL)
This slide shows very delicate fibrinoid necrosis
in the wall of a small artery in the thalamus.
Produced by the Dept. of Neuropathology, Southern
General Hospital, Glasgow).
Neuropathology of Human African Trypanosomiasis
Acute haemorrhagic leucoencephalopathy This
slide shows the foci of haemorrhage around small
blood vessels. Produced by the Dept. of
Neuropathology, Southern General Hospital,
Glasgow).
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Diagnosis

• Trypansosomiasis is best diagnosed by
  demonstration of parasites in blood smears, lymph
  node exudates or spinal fluid
• Parasitemia can be very low at times resulting in
  false negative results. It is more likely to find
  parasites during symptomatic periods.
• Several techniques can be used to enrich rare
  parasites in blood sample (centrifugation,
  chromatography).
• The Card Agglutination Test for Trypanosomiasis
  (CATT).  Serodiagnostic test to identify anti-T.
  brucei antibodies (gambiense).

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Diagnosis

• At later stages of the disease there might be no
  detectable parasites in the blood
• Lumbar puncture and microscopic identification of
  parasites and detection of elevated protein
  levels in the CSF are needed for diagnosis
• Establishment of CNS infection is important for
  therapy decisions

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Drugs for Human African Trypanosomiasis
Suramin (T. b. rhodesiense) Parenteral
administration (i.v.). Inactive in all late stage
disease. Prolonged treatment (up to 3
weeks) Toxicity (fatal anaphylaxis 1 in 20,000
skin reactions, reversible renal damage). (Bayer)
Pentamidine (T. b. gambiense) Parenteral
administration (i.m.). Inactive in some
T.b.rhodesiense cases. Inactive in all late stage
disease. Toxicity (e.g. hypotension, myalgia,
sterile gluteal abscess, diabetes). Cost (
60-150)
Melarsoprol Parenteral administration (slow i.v.
infusion). Active on late stages. Prolonged
hospitalization. Severe toxicity (death 5
encephalopathy 10 pruritus, cardiac failure)
High relapse rate (drug resistance?). (Aventis)
Eflornithine (D,L-?-DFMO) Parenteral
administration (i.v. infusions). Inactive against
T.b.rhodesiense late stage. Prolonged treatment
(up to 3 weeks). Reversible toxicity
(convulsions bone marrow suppression GI
symptoms nerve deafness). Future availability a
problem and cost (Aventis)
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Treatment (haemolymphatic phase)

• Suramine discovered 1921 (rhodesiense)
• Suramine will also kill O. volvolus microfilariae
  which can cause anaphylactic shock
• Pentamidine discovered 1941 (gambiense)
• Drug resistance is on the rise

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Treatment (menigoencephalitic phase)

• Melarsoprol is an organic arsenical developed in
  1949
• It is the only drug effective against late stage
  rhodesiense infection
• Fatality due to severe acute reactive
  encephalopathy can be 1-10
• Drug resistance is a growing problem in
  rhodesiense
• Severe long term neurological (side) effects even
  after successful treatment possible

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Treatment (menigoencephalitic phase)

• Difluoromethylornithine (DMFO, eflornithine) is a
  more recently developed drug
• It is less toxic and quite effective
  (resurrection drug) but only effective against
  gambiense. Other problems 20 of patients
  relapse resistance.
• Target of DMFO and several other trypanosome
  drugs is the parasites polyamine metabolism which
  is critical for redox balance
• Production of DMFO and other drugs almost ceased
  due to low commercial potential

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Gambiense and Rhodesiense Sleeping sickness

• West African
• T.b.gambiense
• West Central Africa
• Tsetse fly (Glossina, palpalis group)
• Reservoir human
• Parasitemia low/variable
• Clinical features
• Early fever, myalgias, lymphadenopathy, edema,
• Late CNS seizures, coma
• Duration months-years
• Mortality 100 if unRx
• Asymptomatic carriers common

• East African
• T.b. rhodesiense
• Rift valley eastern Africa
• Tsetse fly (Glossina, morsitans group)
• Reservoir wild animals
• Parasitemia high
• Clinical features
• Early severe fevers, edema, weakness, emaciation
• Late rapid demise
• Duration weeks - months
• Mortality 100 if unRx
• Asymptomatic carriers rare

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New cases of Sleeping Sickness reported for all
Africa between 1927 and 1997
In the early part of the twentieth century, HAT
decimated the population in many parts of
sub-Saharan Africa. In the 1930s, the colonial
administrations, conscious of the negative impact
of the disease on its territories, established
disease control programmes. Systematic screening,
treatment, and follow-up of millions of
individuals in the whole continent led to
transmission coming to a near halt by the 1960s.
With the advent of independence in most countries
where HAT was endemic, the newly independent
authorities had other priorities to deal with.
The rarity of HAT cases, and a decline in
awareness of how the disease could return, led to
a lack of interest in disease surveillance. Over
time the disease slowly returned, and some thirty
years later, flare-ups were observed throughout
past endemic areas. PLOS Medicine, 5 e55. (2008)
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Increase in Trypanosomiasis 1988-1997, Tambura
County, Sudan in the 13 Villages of Ezo
Payam1995 18 cases 1996 87 cases
(CI 17.7, 23.1)
(100)
epidemic level 2

1988 1997
1988 1997
prevalence
villages with SS
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Cases of African Trypanosomiasis (DRC Angola)
25,094 cases reported in 1997
estimated annual incidence gt 100,000

• 15-20 of population
• at risk is
• under surveillance
• estimated annual
• incidence gt150,000

Democratic Republic of Congo
Angola
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African trypanosomiasisCurrent Situation

• Classic example of an emerging (1890-1930) and
  re-emerging (1990) infection
• A leading public health problem, 1st half of
  1900s
• Brought under control by 1950-1960 using mass
  campaigns (active surveillance and treatment
  chemoprophylaxis - pentamidine every 4-6 months)
• Re-emerging in central Africa, following reduced
  (or no) control activities in 1990s
• Between 1995 and 2006, the total number of new
  cases reported was reduced by 68. This is due to
  a strong advocate from WHO leading to stronger
  surveillance and control measures in endemic
  countries through training and the provision of
  equipment for screening, diagnosis, and treatment.

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Epidemiological Status of Countries considered
endemic for Trypanosomiasis
36 sub-Saharan countries are considered endemic
for one or the other form of the disease, despite
the fact that some of them have reported no cases
in the last decade
34
Nagana is the major impediment to cattle
production in Africa

• Also African Animal Trypanosomosis/trypanosomiasis
  (AAT)
• Almost the entire area of sub-Saharan Africa
  which is suitable for cattle is Tsetse infested
• High losses due to anemia and cachexia especially
  in productive breeds

35
Nagana

• Nagana means in Zulu to be in low or depressed
  spirits
• Nagana is caused by T. brucei brucei (tissue
  parasite), T. congolense and T. vivax (hematic
  parasites).
• Most important in cattle but can also produce
  serious losses in pigs, camels, goats, and sheep
• Fever, anemia, occasional diarrhea, and rapid
  loss of conditions and often death.
• Several drugs are available for treatment
  (berenil) and prophylaxis (samorin, trypamidium
  chloride), but resistance is a problem.

36
Nagana
Trypanosoma congolense

• T. congolense is a group of small trypanosomes,
  med-size kinetoplast, no free flagella and poorly
  developed undulating membranes.
• It is considered to be the single most important
  cause of AAT in East Africa. Sheep, goats,
  horses, and pigs may also be affected. In
  domestic dogs, chronic infection often results in
  a carrier state.

37
Nagana
Trypanosoma vivax

• T. vivax are trypanosomes with large terminal
  kinetoplasts, distinct free flagella, and
  inconspicuous undulating membranes. T. vivax is a
  large (18-26 µm long) monomorphic organism.
• Cattle, sheep, and goats are primarily affected.
  Less pathogenic for cattle than T. congolense,
  but it is the most important cause of AAT in west
  African cattle.
• T. vivax persists in areas free of tsetse flies
  (for example, in Central and South America and in
  the Caribbean), where it is transmitted
  mechanically by biting flies or contaminated
  needles, etc.

38
Nagana

• Several local breeds of cows, goats, sheep etc.
  show trypano-tolerance
• Animals get infected but have the ability to
  control parasitemia better, as well as to survive
  higher parasite burdens

39
Wild animals are important reservoirs HAT and AAT

• More than 30 species of wild animals can be
  infected with trypanosomes
• Many remain carriers
• Ruminants are known to be active reservoirs.
• Wild Equidae, lions, leopards, and wild pigs
• are susceptible and can also serve as carriers
  of trypanosomes.

40
Tse tse flies
http//www.biosci.ohio-state.edu/parasite/home.ht
ml
There are about 30 known species and subspecies
of tsetse flies belonging to the genus Glossina.
Characteristic pointing mouth part ( proboscis).
Two groups of medical importance (important
species for transmission of sleeping sickness) G.
palpalis group found mainly in riverine woodland
of west and central Africa (G. fuscipes and G.
palpalis subspp.) G. morsitans group found
mainly in savannah woodlands across sub-Saharan
Africa (G. pallidipes. G. morsitans sbspp., G.
longipennis and G. austeni)
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Tse tse flies

• Vectors of T. b. gambiense e.g. G. tachinoides
  and palpalis breed near water sources making
  rivers and ponds major transmission sites
  (gambiense can occur in massive epidemics)
• G. morsitans the vector for rhodesiense occurs in
  scrub savannah country

42
Tse tse flies are viviparous
The female tse tse fly produces larvae, one at a
time. The egg hatches within the female and the
larva develops in the female. During her
life-span a female can only produce a maximum of
8-10 offspring.  The larva is laid onto the
ground (larviposition). The female finds a
suitable place to lay the larva. In damp areas
females tend not to concentrate their
larviposition in particular areas. In dry areas
larviposition takes place mainly in well-shaded
spots.
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Tse tse flies are viviparous

• The freshly-laid free-living larva, does not need
  to feed and burrows into the soil where its skin
  hardens and blackens into a puparium and within
  the puparium, pupation and metamorphosis take
  place.

44
Control measures for African trypanosomiasis
Removal of vegetation. In savanna areas,
larviposition occurs in shaded places, so one
control method is to remove trees and bushes so
only grass is left. Labor intensive and requires
that there be re-slashing of vegetation on an
annual basis. The method fell into disuse with
the advent of insecticides. Killing of wild
animals. To remove reservoirs of infection in the
wild animal populations. This method was used
extensively in the past. Drugs. Animals can be
given drugs to kill Trypanosomes. Sterile
insect technique (SIT). This method involves
breeding up thousands of male Glossina which are
sterilized using radiation and then released at
regular intervals, thus swamping the population
with males that are unable to fertilize females
successfully. Spraying of insecticides. Two
main approaches have been used (1) spraying of
residual insecticides that persist in the
environment for at least 2-3 months and (2)
spraying of non-residual aerosols that kill adult
tsetse at the time of spraying but which must be
repeated at regular intervals in order to kill
newly emerged adults. Both ground and aerial
application methods have been used. Aerial
methods are expensive but have been used with
success.
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Control of Tse tse flies

• Tse tse control can include spraying of large
  areas, release of sterile males, and insecticide
  dips for cattle
• Special fly traps are one of the most effective
  devices especially for the control of riverine
  gambiense transmission

The insecticides applied to cattle to control
tsetse are not repellents and they do not prevent
tsetse from biting cattle . However, each fly
that bites - or even touches - a treated animal
will die within a few hours. Hence, if enough
cattle are treated then the population of tsetse
will be reduced.
46
Control measures Trapping
A number of different traps have been developed
for capturing tsetse-flies in large numbers. The
biconical trap which is a netting trap that
tapers above and below so it looks like a cone
with another inverted on top. Insecticide-impregna
ted cloth targets that are attractive to the
flies, are also used. Host odor attractants are
used on these traps. 
47
Fake cows help to reduce sleeping sickness and
use of insecticides