SPOTLIGHTS ON NEW PUBLICATIONS

Vol. 6, No. 1, 2013
ISSN: 1687-7942
S P O T L I G H T S O N N E W P U B L I C AT I O N S
PUJ
Trichomonas vaginalis
Trichomonas vaginalis is the most common curable
sexually transmitted infection worldwide. In 2001, WHO
claimed that more than 170 million people are infected
annually with T. vaginalis. It is emerging as a serious
reproductive tract pathogen, mainly affecting people
living in poor or disadvantaged communities. However,
serious adverse reproductive health outcomes including
pregnancy complications, pelvic inflammatory disease
and an increased risk of HIV acquisition have been linked
to trichomoniasis. In this regard, potential mechanisms
for increased susceptibility include (1) recruitment of
HIV target cells (CD4+ T cells) to the genital tract as a
result of the host immune response to T. vaginalis, (2)
degradation of HIV-protective factors such as secretory
leukocyte protease inhibitor, and (3) direct and indirect
cytotoxic effects of the parasite itself. Trichomoniasis is
transmitted through sexual contact or vertically through
vaginal delivery. Men may present with symptoms of nongonococcal urethritis (i.e., urethral discharge, irritation,
or dysuria), whereas the most common symptom in
women is a malodorous vaginal discharge. Women may
also report dyspareunia, dysuria, lower abdominal pain,
or vulvovaginal irritation. However, the majority of the
infected women and men are asymptomatic.
The parasite’s genome sequence was reported in 2007,
and 2 types population structure emerged. Type 1
was easier to detect by wet mount and may represent
symptomatic patients with high parasite loads; while
type 2 demonstrated a significantly higher minimum
lethal concentration of metronidazole necessary to kill
isolates compared with type 1. It was reported that a
double-stranded RNA virus was detected in 73% of type
1 isolates and 2.5% of type 2 isolates. T. vaginalis viruses
induced alteration of the surface expression of P270 and
cysteine proteinases, which conceivably can result in
modulation of its pathogenicity.
There are several sensitive and specific diagnostic
tests available, including a newly approved nucleic
acid amplification test. Metronidazole and tinidazole
can cure trichomoniasis. Systemic therapy is preferred
over topical applications to achieve adequate drug
concentrations in non-vaginal sites such as the urethra
and periurethral glands. Metronidazole-resistant isolates
are estimated to occur in 2.5-5% of cases and increasing
its dose or switching to tinidazole can usually overcome
the resistance.
In the present issue, recent original articles concerning
T. vaginalis prevalence, pathogenicity, immune response,
genomics, diagnosis and treatment will be summarized.
Prevalence: In Iran, various studies determined the
prevalence of trichomoniasis between 2-8% according
to the cultural and social status. To determine its
prevalence among symptomatic and asymptomatic
women in Hamadan city, Iran, M. Matini and his
colleagues presented a descriptive cross-sectional study.
Another objective besides prevalence was to evaluate
the usefulness of the clinical examination and the value
of signs and symptoms in diagnosis of trichomoniasis
in gynecological and obstetrics clinics. The study was
carried out on 750 women from November 2010 to July
2011 excluding cases who had used vaginal antibiotic
during the past 2 weeks. Information regarding vaginal
discharge (color and consistency), itching, dysuria
and dyspareunia was collected, followed by clinical
examination. The discharge was subjected to wet mount
examination and culture technique (Dorset medium). The
culture was examined daily up to 7 days until they turned
positive. Clinical examination revealed 42 T. vaginalis
infected women. Parasitological results showed that the
city had low trichomoniasis prevalence (2.1%); culture
diagnosed 16 cases while wet mount missed only 3 cases.
The highest infection rate was in the age group 25-34
years with statistically significant difference. In addition,
4 asymptomatic cases were not identified by clinical
examination. The sensitivity, specificity and positive
and negative predictive values of clinical diagnosis
compared to culture method (gold standard) were
75%, 95%, 28% and 99%, respectively. On the other
hand, 550 cases (73.3%) showed one or more signs and
symptoms of trichomoniasis; the vaginal discharge was
the most common sign. From the previous results, it was
concluded that 1) clinical signs and symptoms are not
specific for trichomoniasis and are common in all sexual
transmitted disease; 2) diagnosis of trichomoniasis based
on only clinical symptoms is unreliable.
Prevalence of Trichomonas vaginalis infection in
Hamadan City, Western Iran. Iran J Parasitol; 2012,
7(2):67–72.
Pathogenecity and virulence: In a review article, the
Indian scientists Sehgal R, Goyal K and Sehgal A
pointed out the importance of iron as an essential nutrient
for the survival of pathogenic protozoa, especially the
amitochondriate ones such as Trichomonas, Giardia, and
Entamoeba. These protozoa require higher extracellular
iron concentration for their functional energy metabolism
system. On the other hand, ferric irons are chelated by
lactoferrin (Lf), which is an extracellular glycoprotein of
Personal non-commercial use only. PUJ copyright © 2013. All rights reserved
PUJ; 2013, 6(1):121-124
Spotlights on New Publications
the host immune system, so there is a balance between
the invading pathogen and the host immune response
to determine the clinical outcome. This extracellular
glycoprotein has a wide range of biological activities
including regulation of iron absorption in addition to
its antioxidant, anticarcinogenic, anti-inflammatory and
antimicrobial activities. It is found in various mucosal
secretions, including saliva, tears, vaginal fluids, semen,
nasal and bronchial secretions, GIT fluids, urine, milk
and blood. In other words, extracellular iron is bound to
transferrin to be transferred to all cells and at the mucosal
surfaces it is bound to Lf. Meanwhile, Lf exists in two
forms; apo-Lf (without iron) and holo-Lf (saturated with
iron). When apo-Lf acquires iron, it becomes saturated
with iron and forms holo-Lf to be an important source
of iron for microorganisms. The latter developed various
strategies to acquire iron from holo-Lf to be used in
replication causing acute or chronic infections and tissue
damage. The reviewers described 4 strategies; expression
of Lf binding receptors or proteins (Lbps) (e.g. in T.
vaginalis), proteases secretion to cleave holo-Lf releasing
iron (e.g. Tritrichomonas fetus and E. histolytica),
reductases secretion to reduce ferric to ferrous state
(e.g. Leishmania spp.), and the 4th mechanism is used by
bacteria and fungi (xenosiderophores).
It was observed also that trophozoites grown in iron-rich
media become resistant to complement lysis, because iron
regulates parasite cysteine proteinases (CPs) necessary
to provide resistance to complement degradation and to
recognize and bind to host cells (CPs dual role; parasite
survival and tissue damage). Meanwhile, iron downregulates proteolytic activity, expression and transcription
of CPs participating in T. vaginalis virulence e.g. CP65
and CP39 which are involved in cytotoxicity. So, just
before menstruation with low iron concentration and
decreased cytoadhesion, CP65 and CP39 are activated to
help the parasite moving in search of iron to maintain
its virulence. On the other hand, the major surface
immunogen (P270) is a protein characterizing T. vaginalis
phenotypic variation. According to P270, there are 2
genotypes, I and II; and it was shown that iron played an
important role in modulating surface localization of P270
in virus-harboring parasites.
Finally, the authors recommended further studies to
evaluate drugs which can target the holo-Lf receptor
or inhibit Lf binding sites to provide immunity against
trichomoniasis. Further studies are also required to test
using T. vaginalis receptor-mediated mechanism as a
vaccine candidate.
In the receptor mediated mechanism, T. vaginalis
recognizes human holo-Lf by two surface proteins;
178 and 75 kDa. Increased Lbps activity was observed
in response to iron-depleted conditions. This means
increased number and affinity of Lbps in in vitro T.
vaginalis cultivated under iron-depleted conditions or
in vivo, keeping in mind that Lf concentration in human
vaginal mucosa fluctuates from 9-200 μg/ml during
the menstrual cycle. The reviewers discussed different
roles of iron on growth, cytoadherence and virulence
of T. vaginalis in vitro. Shorter trophozoites generation
time and significant lethal effects of metronidazole in
low concentration were observed in iron-rich media.
For cytoadherence (as an initial step in pathogenesis),
trophozoites isolated from iron-rich media showed
higher level of cytoadherence in proportion to iron
concentration. To colonize the vaginal epithelium, T.
vaginalis trophozoites evolved several adherence factors
such as adhesion proteins (APs), lipophosphoglycan,
α-actinin, enolase, phosphoglucomutase, and various
binding proteins (fibronectin, laminin and GTP). The
majority of APs are positively regulated by iron such
as the AP65-1 gene (which encodes 65 kDa malic
enzyme involved in cytoadherence) and AP120 (which
is involved in synthesis of a component localized to the
parasite surface and participates in cytoadherence). The
iron role in T. vaginalis virulence was also discussed.
Trophozoites cultivated in iron-deficient media failed
to produce pathological lesions while those cultivated
in normal Diamond's media or iron-supplemented TYM
media produced subcutaneous abscesses.
Trichomoniasis and lactoferrin: Future prospects.
Infect Dis Obstet Gynecol; 2012, 536037.
Genomics: Previous studies documented the role of
iron components such as cysteine desulfurase, the
molecular scaffold protein (IscU), and cytosolic and
nuclear FeS proteins (e.g. Rli1p) in hydrogenosomes
(specific mitochondria-related organelles), and ribosome
biogenesis and functions. These proteins are essential
for the formation of FeS clusters in the catalytic centers
of apoproteins, which is mediated by iron–sulfur cluster
(ISC) assembly machinery. Recent studies also revealed
regulation at the post-transcriptional level of 2 cysteine
proteases (TVCP4 and TVCP12) by an iron response
protein-like system. In addition, in vitro experiments
showed the important role of iron in regulation of T.
vaginalis cytoadherence to target cells and increase of
its resistance to complement-mediated lysis. Hence, the
role of iron in T. vaginalis gene expression and genome
evolution was investigated in a collaborated study
between scientists of Parasitology and Immunobiology
Departments and the Bioinformatics Center in Czech
Republic and Taiwan. Identification of the mechanisms
underlying the iron-dependent regulation of these
processes was the objective of recent work by Lenka
Horváthová and her colleagues. Prior to their experiment,
T1 T. vaginalis strain was cultivated in either TYM-ironrich (+Fe) or iron-restricted (−Fe) media. Total RNA was
extracted, the contaminating genomic DNA was digested
122
SM Abaza
Immune response: Several previous in vitro studies
revealed secretion of different cytokines from human
neutrophils, monocytes, macrophages and the vaginal
cells as well as from murine lymphocytes on exposure
of cultured cells to T. vaginalis. These cytokines
included interleukins (ILs) such as IL-8, IL-2, IL-1β and
IL-6 and interferon (IFN-γ) and tumor necrosis factor
(TNF-α). However, few studies detected IL-10 secreted
from dendritic cells and macrophages infected with T.
vaginalis. It is well known that IL-10 has an important
anti-inflammatory role and it is secreted by the host
immune response cells, e.g. macrophages, monocytes
and B and T lymphocytes. In addition, immune cells
infected with HIV showed high secretion of IL-10.
Meanwhile, T. vaginalis-infected patients are more likely
to acquire HIV, due to increased IL-10 levels. In an
attempt to determine whether T. vaginalis and T. foetus
stimulated IL-10 from the cultured bovine epithelial
cells, the Brazilain investigators RC VilelaI and M
Benchimo published their short communication work.
Bovine epithelial cells cultures (BOECs) were prepared
and exposed to both JT and K strains of T. vaginalis and
T. foetus (human and bovine parasite, respectively). Each
culture supernatant was collected to determine IL-10
levels. Results showed high IL-10 levels were secreted
from the BOECs exposed to T. foetus, compared to
control cells. While on exposure to T. vaginalis, IL-10
levels remained at baseline and increased only slightly
compared to controls. The investigators concluded that
the host immune cell response in trichomoniasis is
species-specific.
and the complementary DNA was reconstructed. The
investigators screened iron-regulated genes using T.
vaginalis oligonucleotide microarray analysis and
expressed sequence tag (EST) sequencing of cDNA
libraries derived from trichomonads cultivated under +Fe
and −Fe conditions. Using microarray analysis, results
revealed the presence of 195 genes that were significantly
regulated by iron, of which the 117 and 78 genes were
upregulated in cells cultivated under +Fe and −Fe
conditions, respectively. Using EST approach, 19,074
ESTs were sequenced from distinct cDNA libraries, and
the results revealed 336 genes, of which 165 and 171
genes were upregulated under +Fe and −Fe conditions,
respectively. The investigators discussed the major ironregulated pathways for proteins involved in carbohydrate
metabolism; glycolysis and energy metabolism. As
regards the former, it was shown that enzymes supplying
substrates to the glycolytic pathway were significantly
upregulated under +Fe conditions. For energy
metabolism, malate (ME) is able to serve as a substrate
for hydrogenosomal energy metabolism under +Fe
conditions; while under −Fe, malate is metabolized in the
cytosol via pyruvate to lactate. However, the investigators
found four gene copies for ME, whose expression was
not iron dependent. The majority of genes encoding
amino acid metabolism were significantly upregulated
under +Fe conditions. In contrast to genes encoding
proteins involved in carbohydrate and amino acids
metabolism, genes encoding ISCs assembly machinery
and certain cysteine proteases were upregulated under
−Fe conditions. The expression of 16 genes coding for
cysteine proteases and metallopeptidases was found
to be regulated by iron, and 9 of these genes were
upregulated under −Fe conditions. For hydrogenosomal
membrane proteins, only 2 proteins showed significant
iron-dependent regulation; AAC-1 (upregulated under
−Fe conditions) and AAC-2 (upregulated under +Fe
conditions). With limited iron conditions and increased
AAC-1 expression, ATP is transported from cytosol to
hydrogenosomes. Finally, for the genes encoding proteins
involved in the regulation of transcription and translation
(including ribosomal proteins and proteins affecting
DNA metabolism), only five genes were significantly
regulated by iron. One gene was upregulated under +Fe
conditions, and the other 4 were upregulated under −Fe
conditions. The investigators concluded that iron has
broad critical effects on T. vaginalis’s transcriptome as
iron regulated the expression of a single gene, whereas
the expression of other paralogous copies of the gene was
iron independent.
Short communication: IL-10 release by bovine
epithelial cells cultured with Trichomonas vaginalis
and Tritrichomonas foetus. Mem Inst Oswaldo Cruz
(Rio de Janeiro); 2013 Feb, 108(1):110-2.
Diagnosis: The estimated prevalence of trichomoniasis in
men ranges from 0-58% in asymptomatic men and highrisk adolescents. In symptomatic men, trichomoniasis
was associated with urethritis and prostatitis. Chronic
prostatitis or chronic pelvic pain syndrome (CP/CPPS)
is the most common form of prostatitis, with no existing
reference standard for diagnosis (so, the condition is
mostly recurrent). One of the most common causes of
infection in chronic prostatitis is trichomoniasis (15%).
Trichomoniasis also was incriminated in 13% of patients
with non-gonococcal urethritis (NGU). Diagnosis of T.
vaginalis in men using PCR was the main objective of
a study conducted in Korea by Jong Jin Lee and his
colleagues. They used primers based on a repetitive
sequence cloned from T. vaginalis (TV-E650). These
primars were used previously by the same investigators
and proved 100% (sensitivity and specificity) to detect T.
Transcriptomic identification of iron-regulated and
iron-independent gene copies within the heavily
duplicated Trichomonas vaginalis genome. Genome
Biol Evol; 2012, 4(10):1017–29.
123
Spotlights on New Publications
Treatment: Metronidazole (MTZ) is considered as
a drug of choice for trichomoniasis with a cure rate of
approximately 95%; but clinical resistance was reported
since 1962. In their work, the Iranian investigator Hossein
A. Youse and his colleagues investigated herbal plants
in treatment of trichomoniasis in vitro in comparison
to MTZ. They used TYIS culture medium containing
isolated T. vaginalis with different concentrations of
alcoholic and watery extracts of Iranian plants; Stachys
lavanduifolia, Echinophora platyloba and Eucalyptus
camaldulensis. The parasite number in each test tube
was counted after 24, 48 and 72 h incubation. The results
showed that MTZ (5 μg/ml), E. camaldulensis (60 or 90
μg) had significant effects on parasite count after 72 h,
while no significant effect on T. vaginalis growth was
observed on using alcoholic or watery extract of either
S. lavandulifolia or E. platyloba. The authors discussed
the antibacterial and antifungal effects of Eucaliptus
spp. essential oil against several microorganisms such
as Staphylococcus aureus, Esherichia coli and Candida
albicans; in addition to its anti trypanosomal activity in
vitro. Accordingly, the investigators concluded that E.
camaldulensis could be used as an alternative drug for T.
vaginalis treatment. They recommended further studies
to recognize the efficient components of this plant to be
used with unique efficiency against infective vaginitis;
whatever the cause, bacterial, fungal or parasitic.
vaginalis in vaginal discharge fluid at low concentration
of 1 cell/per PCR mixture. In the present study, PCR
was used to diagnose trichomoniasis in 33 male patients
with chronic recurrent prostatitis and/or urethritis as
well as in 84 male outpatients without lower urinary
tract symptoms. Specimens used in the study were
expressed prostatic secretion (EPS) and first-void urine
and midstream urine samples of pre- (VB1 and Pre-M),
and post-prostatic massage (VB3 and Post-M). Chronic
prostatitis or urethritis were diagnosed by Pre-M and
Post-M urine specimens, while EPS, VB1 and VB3
urine sediments were used for culture in TYM media.
In a PCR technique, the specificity of the primers was
tested against DNA extracted from Candida albicans,
Chlamydia trachomatis, Neisseria gonorrhea, and
Escherichia coli. Results showed that culture failed to
diagnose trichomoniasis, whereas PCR identified 7 cases
(21.2%), 5 of whom were diagnosed with prostatitis and
2 with urethritis. Positive PCR results were reported in
bothVB1 and VB3 in all prostatitis cases and only in
VB1 for urethritis patients. All the control patients (No.
84) gave no positive results for T. vaginalis neither by
PCR nor by culture. The investigators concluded that
PCR using urine specimens is more sensitive than culture
for diagnosis of trichomoniasis, and recommended PCR
screening among men with recurrent prostatitis and
urethritis as a part of routine checking in public health
units to control trichomoniasis.
Effect of Echinophora platyloba, Stachys lavandulifolia,
and Eucalyptus camaldulensis plants on Trichomonas
vaginalis growth in vitro. Adv Biomed Res; 2012, 1:
79.
PCR for diagnosis of male Trichomonas vaginalis
infection with chronic prostatitis and urethritis.
Korean J Parasitol; 2012 June, 50(2):157–9.
Compiled by
Prof. Dr. Sherif M. Abaza
Parasitology Department, Faculty of Medicine
Suez Canal University, Ismailia, Egypt.
Email: smabaza@hotmail.com
124
Vol. 6, No. 1, 2013
ISSN: 1687-7942
PA R A S I TO L O G I C A L R E S O U R C E S
1. TropEduWeb-Swiss tropical Institute: Web-basedLearning Tools for Tropical Medicine and Parasitology:
http://www.tropeduweb.ch/: This web site is maintained
by the Swiss Tropical Institute (STI) which undertakes
research, teaching/training and provides services in
the fields of tropical medicine, travel medicine and
international health. STI is an associated institute of
the University of Basel. Many members of the STI
staff hold teaching posts (professors, senior lecturers)
at the University of Basel in the faculties of Sciences,
Medicine, and Arts (Ethnology). The site is intended to
provide interactive web-based learning with continuous
auto-evaluation and formal assessments based on the
specific teaching and learning objectives. The learning
process is user-driven and covers the full spectrum from
acquiring information/knowledge to conceptualising and
conceptualising complex systems based on theories and
case studies.
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diagnosis and treatment. The second page has pictures
and videos.
5. John Hopkins School of Public Health Malariology
Course: http://ocw.jhsph.edu/index.cfm/go/viewCourse/
course/malariology/coursePage/index/: This is a free
web course which presents issues related to malaria
as a major public health problem. It emphasizes the
biology of malaria parasites and factors affecting their
transmission to humans by anopheline vectors. Topics
include host-parasite-vector relationships; diagnostics;
parasite biology; vector biology; epidemiology; host
immunity; risk factors associated with infection, human
behavior, chemotherapy, and drug resistances; antivector measures; vaccine development; and management
and policy issues.
2. Schistosomiasis Research Group-University of
Cambridge: http://www.path.cam.ac.uk/~schisto/index.htm:
This site is intended to convey information not only
on the research that is carried out by Schistosomiasis
Research Group at Cambridge University, but also all
aspects of schistosomiasis as a tropical parasitic disease.
Other helminth infections are also covered, although in
less detail.
6. History of Parasitology and Tropical Medicine:
http://dna.kdna.ucla.edu/parasite_course-old/intro_files/
intro1.htm: This website shows the history of eminent
Parasitologists who contributed to the discovery of
parasites starting from the 17th century when the Dutch
amateur scientist Anton van Leeuwenhoek discovered the
first protozoan parasite, Giardia, till the late seventies of
the 20th century when Trager and Jensen, at Rockefeller
University in New York, discovered a simple method
to grow the pathogenic human malaria, Plasmodium
falciparum, in continuous culture inside red blood cells.
3. PLOS Neglected Tropical Diseases Journal: http://
www.plosntds.org/ PLOS Neglected Tropical Diseases
(eISSN 1935-2735) is an open-access journal devoted to
the world's most neglected tropical diseases (NTDs), such
as elephantiasis, river blindness, leprosy, hookworm,
schistosomiasis, and African sleeping sickness. The
journal publishes high-quality, peer-reviewed research on
all scientific, medical, and public-health aspects of these
forgotten diseases affecting the world's forgotten people.
PLOS Neglected Tropical Diseases is published online
by PLOS, a nonprofit organization. The journal's start-up
phase is supported by a grant from the Bill and Melinda
Gates Foundation. PLOS Neglected Tropical Diseases is
indexed in PubMed, PubMed Central, Scopus, Google
Scholar, and the Web of Science.
7. Introduction to Diagnostic Medical Parasitology:
Swiss Tropical and Public Health Institute: http://
www.parasite-diagnosis.ch/: This learning software
allows beginners to gain experience in diagnosing the
most important helminth and protozoan diseases of
humans. For this purpose, one can gain basic knowledge
through short overviews of parasites, diseases, diagnostic
methods and strategies. Even more important, one can
train diagnostic capabilities using a virtual microscope.
The course leads the student from basic training to
more complicated diagnostic exercises. The underlined
purpose is to facilitate a first approach to Diagnostic
Medical Parasitology. This programme cannot replace
working with a real microscope or consulting diagnostic
textbooks and atlases.
4. Parasites in Humans Organization: http://www.
parasitesinhumans.org/ This website is all about parasitic
infections caused by worms, protozoa and skin parasites.
Each parasite species has two pages. The first of the two
contains basic information such as: life cycle, symptoms,
Compiled by
Prof. Dr. Khalifa E. Khalifa
Parasitology Department, Faculty of Medicine,
Ain Shams University, Cairo, Egypt.
Email: klkhalifa@hotmail.com
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