Introduction
The World Health Organization (WHO) has recently announced its plan to eliminate Human
African trypanosomiasis (HAT). The plan's main focus is on the Trypanosoma brucei
gambiense subspecies, which causes 97% of cases [1]. However, total elimination from
certain areas has proved extremely difficult previously; there has been ongoing parasite
detection in several foci in West Africa, despite effective screening programmes.
This has focussed interest on the potential role of asymptomatic human carriers in
contributing to transmission. In this report, we present a unique case of a patient
harbouring the parasite for more than three decades before developing stage 2 sleeping
sickness [2].
Presentation Of Case
A 62-year-old male (see Fig. 1 for summary timeline) was admitted to Bridgend hospital
in Wales in March 2012. He presented with a 3-month history of worsening mobility,
shuffling gait, fatigue, somnolence, emotional lability, and personality change. Born
in Eastern Sierra Leone, he had moved to the United Kingdom in 1971, making two visits
back to his home country, the last of which was for 3 months in 1983, with no subsequent
travel to Africa.
10.1371/journal.pntd.0003349.g001
Figure 1
Timeline of the patient's clinical course.
Timeline is not to scale. Abbreviations: Ab: Antibody ANA: anti-nuclear antibody,
ANCA: anti-neutrophil cytoplasmic antibody, BM Bx: bone marrow biopsy, CSF: cerebrospinal
fluid, ED: Emergency department, ENA: extractable nuclear antigens, ESR: erythrocyte
sedimentation rate, Hb: haemoglobin, LP: lumbar puncture, MRI: magnetic resonance
imaging, NECT: nifurtimox-eflornithine combination therapy, NMDA: N-methyl-D-aspartate
receptor, PEX: Plasma exchange, PCR: polymerase chain reaction, Plts: platelets, Rx:
treated with, VGKC: complex voltage gated potassium channel-complex, WCC: white cell
count.
In 2000, during investigation of venous leg ulcers, he was found to have a normocytic
anaemia (Hb 10.4 g/dl, (13.0–17.0)), and erythrocyte sedimentation rate (ESR) of 78
mm/hour, (1–20). Elevated titres of anti-nuclear antibodies (1∶100), anti-nuclear
cytoplasmic antibodies (1∶160), and Anti-Ro antibodies were detected. There were no
sicca symptoms and no specific treatment for autoimmune disease was instituted. He
was kept under annual review; the only medication given was tiabendazole in 2005 for
a persistent eosinophilia and positive Strongyloides serology.
In 2007 a pituitary adenoma (with a normal hormone profile) was detected on magnetic
resonance imaging (MRI) of the brain during investigation of a unilateral lower motor
neurone seventh nerve palsy. In 2008 a diagnosis of “atypical Sjögren's syndrome”
was made in light of persistent autoantibodies. At this stage his haemoglobin was
9.4 g/dl, platelets 125×109/L (150–400), ESR 127 mm/hr, Immunoglobulin M (IgM) levels
were 20.6 g/L (0.4–2.3), and Immunoglobulin G (IgG) levels 32.6 g/L (7.0–16.0). In
2009 he was started on prednisolone 10 mg daily following an episode of epiglottitis.
Azathioprine was added and increased to a dose of 100 mg daily.
In 2010 the patient developed unilateral thigh swelling and a transient rash. Borrelia
burgdorferi serology (IgM & IgG) was positive and he received 2 weeks of doxycycline.
Elevated anticardiolipin antibodies were detected and he was prescribed aspirin (subsequently
discontinued due to epistaxis). A bone marrow examination was advised to investigate
persistent anaemia and thrombocytopenia, but the patient declined.
In 2011 osteoporosis was discovered on a Dual-energy X-ray absorptiometry (DEXA) scan;
low testosterone levels and high prolactin levels (70,400 U/L) prompted treatment
with testosterone gel and cabergoline. MRI of the brain showed no change in the pituitary
adenoma. The “Sjögren's” diagnosis was reconsidered, azathioprine was discontinued
and prednisolone reduced to 2.5 mg daily. Until this point in the history, the patient
had remained relatively well, with no symptoms beyond those mentioned above. Indeed,
his wife stated “he had never missed a day of work in his life.”
In January 2012, the patient developed unsteadiness and had three falls at home. He
was admitted to hospital in March 2012 with rapidly deteriorating mobility, alteration
in his sleep–wake cycle, and episodes of drowsiness. Neurological examination demonstrated
rigidity, bradykinesia, and a right lateral gaze palsy. An initial diagnosis of Parkinsonism
resulted in treatment with carbidopa/levodopa with minimal benefit. A few days into
his admission, he developed fevers and longer sustained episodes of unresponsiveness.
He was treated for possible meningoencepalitis with aciclovir and ceftriaxone. Hydrocortisone
(400 mg daily) was commenced to cover pituitary apoplexy which was subsequently excluded
on imaging. A cerebrospinal fluid examination revealed 250 lymphocytes/mm3, protein
0.57 g/L, and a normal glucose ratio; gram stain, bacterial culture, and PCR for herpes
viruses were negative.
An MRI of the brainrevealed nonspecific white matter changes around the basal ganglia
and multiple radiolucent lesions in the skull vault. Serum and urine electrophoresis
did not detect a paraprotein, and a skeletal survey was normal. HIV and treponemal
serologies were negative. Since the patient continued to experience symptoms of drowsiness,
a diagnosis of encephalitis lethargica was entertained. Further results demonstrated
high levels of voltage gated potassium channel–complex (VGKC-complex), antibodies,
and moderate levels of N-methyl-D-aspartate (NMDA) receptor antibodies. He developed
further episodes of unresponsiveness, and a generalised tonic-clonic seizure followed
by persistent coma prompted transfer to a neurology ward with a view to intravenous
immunoglobulin for a presumed autoimmune encephalitis. Meanwhile, microscopy of a
bone marrow trephine demonstrated multiple Trypanosoma brucei trypomastigotes, subsequently
seen in the peripheral blood. He was intubated, and on 5 May, urgent airborne transfer
to the critical care unit at the Hospital for Tropical Diseases in London was arranged.
Treatment was commenced immediately with NECT (nifurtimox-eflornithine combination
therapy), with oral nifurtimox 5 mg/kg every 8 hours and intravenous eflornithine
200 mg/kg every 12 hours, which is the recommended first-line therapy for stage 2
HAT [1]. NECT was chosen over the eflornithine monotherapy (the alternative treatment
for stage 2 HAT), since it has shown to be equally efficacious whilst causing less
severe haemotological side effects. Furthermore, treatment with NECT is of shorter
duration and requires fewer infusions, minimizing the chance of line related complications
[1].
On Day 4 of the Intensive Therapy Unit (ITU) admission, the patient was promptly extubated
and transferred to the ward shortly afterwards, with complete reversal of coma and
resolution of pancytopenia. Cerebrospinal fluid (CSF) examination revealed a positive
indirect fluorescent antibody test (IFAT) for T. b. gambiense, with a titre of 1/32,
and serum IFAT was positive at 1/3200. Analysis of a stored serum sample from 2004
demonstrated a T. b. gambiense IFAT titre of 1/800.
On Day 9 of NECT treatment the patient started to become drowsy once again, requiring
reintubation. A computed tomography (CT) scan of the brain showed no acute changes.
Repeat CSF and blood exams showed no evidence of trypanosomes. Nonconvulsive status
was excluded by electroencephalogram. Because of the laboratory evidence of effective
treatment and the overlap in clinical features of autoimmune encephalitis with persistently
high VGKC-complex antibodies, plasma exchange (PEX) was commenced. After four cycles
of PEX, the patient showed clinical improvement and was extubated. Unfortunately,
following further neurological deterioration, the patient was reintubated and a surgical
tracheostomy inserted. Repeat lumbar puncture showed improvement of CSF markers (protein
0.43 g/L, white cells 8/mm3) with no trypanosomes observed in CSF or blood. All subsequent
films were negative. Sleep–wake cycle disturbance continued for the next few weeks
with occasional apnoeic episodes, and resulted in a decision to administer a further
five cycles of PEX, which was followed by sustained recovery (associated with a decline
in VGKC-complex antibodies below the “positive” threshold of 100pM) and discharge
home in August 2012. At outpatient review 1 month later, all extrapyramidal features
had resolved, with considerable improvement in mobility and cognition. Repeat CSF
examinations in February (CSF: Protein 0.27, 8 lymphocytes, CSF T. b. gambiense IFAT
1∶8) and October 2013 (CSF: protein 0.27, 0 lymphocytes, CSF T.b.gambiense IFAT 1∶8)
reflected the ongoing clinical recovery.
Case Discussion
Trypanotolerance
To date, this case represents the longest duration of HAT infection ever reported.
As our patient last visited an endemic country in 1983 and became unwell in 2012,
the period from infection to stage 2 symptoms must have been at least 29 years.
This case provides concrete evidence behind the emerging concept of “human trypanotolerance,”
which challenges the traditionally held view that, left untreated, HAT always progresses
to the fatal stage 2 phase. Checchi, et al., reviewed the prior trypanotolerance literature,
which consists of cases showing an extended duration of infection, like the one discussed
above, as well as cohorts demonstrating spontaneous resolution of infection [3]. We
have summarised and updated the key evidence in this review, illustrated geographically
in Fig. 2
[4]–[12]. In our case, we were able to demonstrate the presence of long standing HAT
infection, using several molecular techniques that were not available in the past.
First, historically, it had not been possible to confirm whether chronic infections
were due to pathogenic trypanosome species, as diagnosis was based on microscopy,
which does not allow differentiation of sub-species [3]. However, PCR amplification
of our patient's parasite DNA clearly indicated T. b. gambiense group 1 [13]. Second,
retrospective testing of a serum sample in 2004 demonstrated clear evidence of serological
infection prior to disease. Third, additional microsatellite typing showed clustering
with field isolates taken from West Africa in the 1980s (Fig. 3), which is the estimated
time our patient would have been first infected. Our findings are consistent with
a recent 15-year follow-up study of untreated stage 1 HAT patients in the Ivory Coast,
which showed that whilst some patients progress to stage 2, a proportion of patients
become asymptomatic carriers, and another subset appears to self cure [7].
10.1371/journal.pntd.0003349.g002
Figure 2
Map showing reports of spontaneous clearance of infection (blue squares), or extended
duration of infection (red squares).
Abbreviations: sc: spontaneous clearance of infection, y: years. References: [4]–[11].
Adapted from [3].
10.1371/journal.pntd.0003349.g003
Figure 3
Phylogenetic tree depicting the relationship between our patient's parasite and field
isolates taken between 1978–1983.
Neighbour joining tree of T. b. brucei, T. b. gambiense group 1 and T. b. gambiense
group 2 isolates from Cote d'Ivoire and T. b. gambiense group 1 isolates from Cameroon
and the Democratic Republic of Congo. Our patient's isolate clustered most closely
with other Type 1 isolates from Cote d'Ivoire.
Elucidating the genetic basis underlying trypanotolerance is of great interest. Although
few parasite factors have been discovered, associations between human genes involved
in the immune response and susceptibility to HAT have been reported [14],[15].
Implications For Public Health And Disease Control
Current disease control strategies rely on case finding and treatment of patients
with detectable parasites in lymph nodes or blood or laboratory evidence of stage
2 disease [16]. Such strategies could fail to stop transmission if there exist hidden
populations of individuals that harbour undetectably low parasite numbers and act
as reservoirs of infection [2],[17]. Evidence that seropositive, microscopy-negative
patients have low-level infection is supported by molecular diagnostic work demonstrating
detectable circulating T. b. gambiense DNA in a proportion of these asymptomatic carriers
[7],[18]. Their potential role in disease transmission is supported by a parasite
population genetic study [19] as well as by research in trypanotolerant cattle [20].
Detecting asymptomatic carriers is particularly challenging due to the lack of a specific
diagnostic test that can be used in remote field settings. However, a recent study
using blood stored on filter paper with the immune trypanolysis test has shown promising
results [21].
As the focus of HAT programs shifts towards elimination of the disease, it is essential
that trypanotolerance is taken into account [22]. Specifically, the following questions
will need to be answered: How common are these asymptomatic carriers? Does their prevalence
vary in different HAT foci? How can they best be detected and monitored? What is the
attributable fraction of transmission associated with failure to detect and treat
such cases?
Immunopathology
Several features of this case generate hypotheses about the immunopathology of HAT.
The factors that led to our patient's development of stage 2 disease after such a
long duration of chronic infection are unknown, but it is feasible that immunosuppressive
therapy (azathioprine and prednisolone) may have played a role. While immunosuppressive
therapy is well described when used for other protozoal infections [23], this is the
first such case reported for HAT. This may be due to the low prevalence of HAT in
populations at risk of iatrogenic immunosuppression. HIV and HAT have considerable
geographic overlap; limited evidence does not suggest an increased risk of HAT among
HIV+ persons [24], but there is no data on the role of HIV in activation of latent
HAT infections, a mechanism well established for Chagas trypanosomiasis [25]. One
can speculate that the immunosuppressive therapy somehow altered the tight balance
between immune control and disease.
The complex clinical course of our patient before diagnosis of HAT warrants attention.
For more than a decade, our patient was diagnosed with a series of conditions (Sjögren's,
Lyme, antiphospholipid disease) based on abnormal serological tests. We consider these
to be false-positive results, due to nonspecific immune activation characteristic
of long-standing HAT infection. Through continuous antigenic variation of their variant
surface glycoprotein, trypanosomes evade the immune system, inducing polyclonal B
cell activation [26], which produces hypergammaglobulinaemia and autoantibodies [27],[28].
We hypothesise that the clinical course of our patient after definitive treatment
may be similarly related to an autoimmune component. Most patients presenting with
stage 2 HAT in field settings respond to treatment with rapid improvement within days.
Whereas it is not uncommon for patients given melarsoprol to develop a post-treatment
reactive encephalopathy, such a syndrome has been described as less frequent with
NECT [29]. Our patient had an uncharacteristically slow improvement following NECT
with a fluctuating sleep disorder lasting several weeks. We believe that this could
be due to immune-mediated encephalopathy. Indeed, our patient was found to be positive
for VGKC-complex antibodies, which are known to cause autoimmune encephalitis [30].
This led us to administer plasma exchange, with clinical improvement mirroring the
fall in antibody titres. One might postulate that VGKC-complex antibodies may therefore
contribute to stage 2 immunopathogenesis. However, a stored serum sample from 5 years
before onset of stage 2 symptoms was also strongly positive (1628 pM; normal range
<100 pM), so other insults must be required to generate pathology, such as the blood-brain
barrier breakdown that must have occurred during the trypanosomal invasion. Improved
understanding of CNS immunopathology is important, as it may help to design better
and safer treatments.
Conclusion
Although we report only on a single patient, this case adds to the accumulating evidence
of human trypanotolerance, thus further stimulating debate about the impact of this
phenomenon in the field and illuminating new avenues of research that must be explored
if we are to provide the answers that are vital for the elimination of this neglected
tropical disease.
Key Learning Points
This case represents the longest duration of T.b gambiense infection ever reported
It adds strong evidence behind human trypanotolerance, which has important implications
for disease elimination programmes
This unique case has revealed interesting aspects of the immunopathology of HAT, which
necessitate further research