ISSN Versión impresa 2218-6425 ISSN Versión Electrónica 1995-1043
Neotropical Helminthology, 2020, 14(1), ene-jun:85-92.
ORIGINAL ARTICLE / ARTÍCULO ORIGINAL
MORPHOLOGICAL CHARACTERIZATION OF THE ROSTELLAR HOOKS OF TAENIA SOLIUM
LINNAEUS, 1758 (CESTODA: CYCLOPHYLLIDEA) METACESTODES EXTRACTED FROM A
NATURALLY INFECTED PIG OF GUATEMALA
CARACTERIZACIÓN MORFOLÓGICA DE LOS GANCHOS ROSTELARES DE METACESTODOS
DE TAENIA SOLIUM LINNAEUS, 1758 (CESTODA: CYCLOPHYLLIDEA) EXTRAÍDOS DE UN
CERDO NATURALMENTE INFECTADO DE GUATEMALA
1Facultad de Medicina Veterinaria y Zootecnia, Universidad de San Carlos de Guatemala, Guatemala
2 Instituto de Investigaciones, Centro Universitario de Zacapa, Universidad de San Carlos de Guatemala,
Guatemala
3Escuela de Medicina Veterinaria, Universidad Mariano Gálvez de Guatemala, Guatemala
*Corresponding author: rhernandezc24@miumg.edu.gt
1 2 3*
Randolf Oliva-Chacón ; Ilde Silva-Feliciano & Roderico Hernández-Chea
ABSTRACT
Keywords: Guatemala – metacestode – morphology – neglected tropical disease – swine cysticercosis – Taenia solium
Taenia solium Linnaeus, 1758 the etiological agent of the taeniasis/cysticercosis complex causes taeniasis
in humans (definitive host), and swine cysticercosis in pigs (intermediate host). Major complications
occur when humans accidentally ingest T. solium eggs and acquire neurocysticercosis, the leading cause
of epilepsy in developing countries. Swine cysticercosis greatly affects rural farmers due to the economic
losses from confiscation or loss of the infected meat. Although the morphological features of T. solium are
well established, limited information is available on the complete morphology of the rostellar hooks of
metacestodes. The objective of this study was to characterize morphologically the rostellar hooks of
metacestodes of T. solium using morphometric features that have not been previously applied for this
species. In addition, a massive infection of swine cysticercosis was described. As part of a pilot study, a
male pig from the department of Zacapa was examined and diagnosed with swine cysticercosis. Lingual
palpation and necropsy were performed and an exceptionally heavy infection was found. The estimated
number of metacestodes was 40,500, of which, 340 were placed in bile solution to estimate the percentage
of viability. Others were used for morphometric analysis of the rostellar hooks. About 97.6% were found
evaginated and with contractile movements. The hooks we found were similar in length and width to other
studies of . Future studies should compare the morphometric parameters of rostellar hooks to T. solium
reject or determine intraspecific morphological variation of T. solium. Morphological features of rostellar
hooks should be considered as a rapid identification guide during necropsies of swine, particularly when
cysts of sp. are found in the viscera. Our findings suggest the presence of high endemic rural areas Taenia
of in Guatemala.T. solium
Neotropical Helminthology
85
Volume14,Number1(jan-jun2020)
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VersiónImpresa:ISSN2218-6425VersiónElectrónica:ISSN1995-1043
Auspiciado por:
doi:10.24039/rnh2020141630
86
RESUMEN
Taenia solium Linnaeus, 1758 es el agente etiológico del complejo teniasis/cisticercosis, causante de
teniasis en el humano (hospedador definitivo) y cisticercosis porcina en los cerdos (hospedador
intermediario). La mayor complicación ocurre cuando los humanos accidentalmente ingieren huevos de
T. solium y adquieren la neurocisticercosis; la causa principal de epilepsia en los países subdesarrollados.
La cisticercosis porcina afecta inmensamente a los productores rurales debido a las pérdidas económicas
por decomisos o pérdida de la carne infectada. Aunque las características morfológicas de T. solium están
bien establecidas, existe limitada información sobre la morfología completa de los ganchos rostelares de
los metacestodos. El objetivo de este estudio fue caracterizar morfológicamente los ganchos rostelares de
metacestodos, utilizando características morfométricas aún no aplicadas en T. solium. Además se describe
una infección masiva por cisticercosis porcina. Como parte de un estudio piloto, un cerdo macho del
departamento de Zacapa fue examinado y diagnosticado con cisticercosis porcina. Se realizó la palpación
lingual y necropsia, y se encontró una alta carga parasitaria, el número estimado de metacestodos fue de
40.500. De los cuales 340 fueron colocados en una solución de bilis para estimar el porcentaje de
viabilidad. El 97,6% fue encontrado evaginado y con movimientos contráctiles. En el análisis
morfológico, los ganchos que se encontraron fueron similares en largo y ancho a los reportados en otros
estudios de T. solium. Futuros estudios deben ser comparados usando los parámetros morfométricos de los
ganchos rostelares para descartar o determinar variación morfológica intraespecífica de T. solium. Las
características morfológicas de los ganchos rostelares deberían considerarse como una guía rápida de
identificación durante las necropsias de cerdos de traspatio, principalmente cuando se encuentran quistes
de Taenia sp. en las vísceras. Nuestros hallazgos sugieren la presencia de áreas rurales altamente
endémicas de T. solium en Guatemala.
Palabras clave: cisticercosis porcina – enfermedad tropical desatendida – Guatemala – metacestodos – morfología – Taenia solium
Swine cysticercosis caused by the larval stage of
Taenia solium Linnaeus, 1758 is a parasitic
infection of pigs causing great economic losses
with public health implications and concerns,
primarily in endemic countries of Latin America,
Asia and Africa (Shonyela et al., 2017). Pigs act as
intermediate hosts of T. solium and rarely present
associated symptoms of swine cysticercosis.
Infection of pigs occurs through ingestion of fecal
material contaminated with eggs of the T. solium
tapeworm from a human carrier, the definitive host.
Consequently, free-roaming pigs from endemic
rural areas with access to human feces are
commonly infected (García et al., 2003a). The
taeniasis/cysticercosis complex is associated with
poverty, lack of sanitation and lack of education. It
is well known that in developing countries the trade
of pigs is usually informal, and the slaughter of
animals is carried out without veterinary inspection
(García et al., 2003b). Thus, the economic losses of
swine cysticercosis are due to the decrease in the
economic value of pigs, or as a result of pork meat
INTRODUCTION
Neotropical Helminthology, 2020, 14(1), ene-jun
confiscation or total loss of the carcasses
(Adesokan & Adeoye, 2019). The diagnosis and
prevalence of swine cysticercosis are very
important considering that this problem
demonstrates an active transmission of the T.
solium life cycle. Unfortunately, in many
developing countries the only available diagnostic
method is the tongue examination, which is highly
specific but with low sensitivity (Sciutto et al.,
1998; Dorny et al., 2004). In Guatemala, few
studies have been carried out regarding swine
cysticercosis, and the actual prevalence is
unknown. Nevertheless, any finding of an infected
pig with T. solium metacestodes is important in
order to determine new foci of the infection,
particularly in remote rural areas, where T. solium
represent a serious threat to the public health.
Although the morphology of the metacestode of T.
solium is well known, there is limited information
of the detailed morphology of rostellar hooks,
considering that most of the studies carried out
have been focused only on the total length and
width of the small and large hooks (Verster, 1969;
Boa et al., 1995). Therefore, the objective of this
Oliva-Chacón et al.
study was to characterize the morphology of the
rostellar hooks of T. solium within Guatemala,
based on the complete morphometric analysis.
Moreover, the intensity of infection with
metacestodes of T. solium in a naturally infected
pig is reported here.
Necropsy and extraction of metacestodes
A male pig of 10 months of age (63 kg) from the
village San Juan (14°55'06"N/89°36'45"O),
municipality of San Jorge, department of Zacapa,
Guatemala, was examined through lingual
palpation due to the report of lingual cysts by the
owner. The mouth was opened with a wooden stick
and the tongue pulled gently with a cotton cloth to
confirm the presence of metacestodes. Afterwards,
the pig was bought and anesthetized. The necropsy
was performed as described elsewhere
(Chembensofu et al., 2017), and the striated muscle
tissue of the carcass, heart, brain, eyes and viscera
were inspected for the extraction of metacestodes.
To determine the intensity of infection by
metacestodes in the carcass, 1 kg composed of
different muscles including the tongue, masseters,
fore- and hind limbs was weighed, and
subsequently, the metacestodes contained in that
kilogram of pork meat were counted using a
manual counter (Assana et al., 2010). After
veterinary inspection, the whole carcass and organs
were incinerated for proper disposal of the
biological material. To estimate the viability of
metacestodes, a number of them were extracted
and washed in 0,9% saline, then placed in Petri
dishes containing a 1:1 mixture of pig bile and
0,9% saline, and incubated at 37°C for 12 h
(Gonzalez et al., 1990). Metacestodes were
considered viable when the protoscolices were
evaginated and displayed contractile movements
under a stereoscopic binocular microscope
(Olympus SZ61). The number of evaginated
metacestodes was counted and the percentage of
viability was determined.
Rostellar hooks morphology
Morphometric analysis was conducted using 50
viable metacestodes. They were placed between
two slides with 70% alcohol for 24 h, and destained
in 5% acid alcohol; then were placed in Petri dishes
87
MATERIAL AND METHODS
with 70% alcohol again, for a few minutes. Then
the cysts were dehydrated in 90% alcohol for 1 h,
then placed in xylene and mounted in Canada
balsam (Chawhan et al., 2014). Nine
measurements were included for morphometric
analysis of the small and large rostellar hooks,
according to Haukisalmi et al. (2011), Fig. 3. The
specimens were observed under a light
microscope, 40X and 10X magnifications (Leica
DM500), and when the rostellum was observed
invaginated not allowing proper observation of the
hooks, the sample was discarded. Drawings of the
hooks were made with the aid of a Lucida camera
attached to the compound microscope. For each
metacestode, the measurements were obtained
from a single small and large hook of each crown.
In addition, the mean, standard deviation (SD) and
range of the morphometric measurements of the
hooks were obtained.
Ethical Aspects: The pig's necropsy was
performed according to the consent of the Animal
Welfare and Bioethics Committee, Facultad de
Medicina Veterinaria y Zootecnia, Universidad de
San Carlos de Guatemala (No.EEP.15.2019).
Necropsy findings
Metacestodes of T. solium were detected first, by
tongue examination and after necropsy, by
dissection of the whole carcass. The intensity of
infection found was extremely high and the
estimated number of metacestodes was 40,500,
which were distributed throughout the striated
muscle tissue, tongue, heart, eyes, and brain (Fig.
1). The metacestodes were small (0.5 mm) and had
intact walls with semitransparent membranes and
transparent vesicular fluid. Three hundred forty
were extracted to determine the percentage of
viability. Out of these, 332 (97.6%) evaginated
after 12 h of incubation. The majority was observed
with movements and with two rows of well-
developed rostellar hooks (Fig. 2A). Few
metacestodes were found with only small hooks
and only one without hooks.
Morphometric analysis
Out of 50 fixed and mounted metacestodes, 25
were used according to an adequate observation of
RESULTS
Neotropical Helminthology, 2020, 14(1), ene-jun Rostellar hooks of Taenia solium
the rostellar hooks. The rostella had 20-26 hooks,
rearranged in two rows (mean=23, n=25). The
small (mean=123 µm, n=25) and large hooks
(mean=163 µm, n=25) were characterized by
having a curved blade. Large hooks had a thickened
88
handle distally and the guard was rounded and
slightly thinner distally. Meanwhile, the small
hooks had a thickened handle in the medial part and
the guard was slightly thinner distally (Fig. 2B,
3B). All hook measurements are shown in Table 1.
Figure 1. Metacestodes of T. solium were found in the whole carcass of the pig. A) Cysts with visible protoscolices were found
during lingual palpation, and during necropsy in B) eyes, C) striated muscle and D) the brain.
Neotropical Helminthology, 2020, 14(1), ene-jun Oliva-Chacón et al.
Figure 2. A) Evaginated metacestodes were observed with a double row of hooks. B) Small and large rostellar hooks of a T. solium
metacestode.
Although we could only examine one backyard pig
for the diagnosis of swine cysticercosis, this
research sample was very important in order to start
new epidemiological surveys and discover new
foci of the taeniasis/cysticercosis complex in rural
89
DISCUSSION communities from Zacapa, Guatemala. The
infection intensity of metacestodes of T. solium
was excessively high, considering that
exceptionally heavy infections are classified from
10,000 metacestodes (Lightowlers et al., 2015).
Since the genus Taenia was erected by Linnaeus
(1758), the most significant morphological
Figure 3. A) Morphometric parameters used for morphological analysis and B) examples of the shapes of the small and large
rostellar hooks of T. solium metacestodes (scale bar 100 µm).
Neotropical Helminthology, 2020, 14(1), ene-jun Rostellar hooks of Taenia solium
Table 1. Measurements (µm) of rostellar hooks of T. solium metacestodes, extracted from a backyard pig (Zacapa,
Guatemala). The morphometric parameters were based on the system used by Haukisalmi et al. (2011).
Small hooks
n=25
Mean Range SD
Total length (TL)
125.9 107-135 6.8
Total width (TW)
45.3 36-55 4.4
Basal length (BL)
66.5 55-72.5 5.0
Apical length (AL)
68.2 62.5-77 3.7
Blade curvature
length
(BCL)
56.7 50-62.5 3.3
Blade curvature (BC)
16.7 15-17.5 1.1
Guard width (GW)
19.1 17.5-25 1.8
Guard length (GL)
20.4 17.5-22.5 1.8
Handle width (HW)
21.7 17.5-25 2.6
Large hooks
n=25
Mean Range SD
Total length (TL)
163.3 150-175 5.9
Total width (TW)
47.5 37.5-57 5.5
Basal length (BL)
81.0 67.5-9 5.5
Apical length (AL)
87.9
85-92.5
5.1
Blade curvature
length
(BCL)
76.6
60-82.5
4.4
Blade curvature
(BC)
15.2
10-17.5
1.91
Guard width (GW)
19.0
15-22.5
2.8
Guard length (GL)
24.1
22-25
1.2
Handle width (HW) 19.3 17.5-25 2.3
available and are suspected to be of T. solium and T.
hydatigena, morphological differentiation should
be considered, specifically when T. hydatigena
metacestodes are immature and small cysts are
found in the liver, lungs and mesentery of pigs.
Although the confirmation of Taenia spp. must be
performed by molecular techniques and
sequencing, morphological analysis can provide a
quick identification guide for the genus Taenia
when necropsies are performed in backyard/free-
roaming pigs from rural communities. Histological
examination for identification of hooks in small
cysts with light microscopy is also recommended
(L'Ollivier et al., 2012). There is limited literature
with morphological descriptions of T. hydatigena
rostellar hooks from swine. However, Filip et al.
(2019) reported a complete morphometric analysis
of metacestodes extracted from the livers of wild
boars (Sus scrofa Linnaeus, 1758). The main
morphological differences concerning the hooks of
T. solium found are the following: The shape of the
blade of T. hydatigena hooks is more curved; the
basal, apical and guard lengths are significantly
larger (77.7-136.3 µm); (85.2-103.1 µm); (30.7-
36.4 µm) and were thicker according to width
measurements (74.3-74.6 µm). Taenia hydatigena
hooks are larger for all morphometric parameters.
Nevertheless, more studies of metacestodes
extracted from pigs of both species, are needed to
accurately determine the morphometric
differences of the rostellar hooks.
This study provides a better morphological
analysis of T. solium metacestodes and can be used
as a quick guide to identify morphological
differences of rostellar hooks, particularly when
unknown cysts of similar size are found in different
organs, primarily those suspected to be of T.
hydatigena. Additionally, a massive infection of T.
solium metacestodes was reported. These results
indicate the probable endemicity and active
transmission of T. solium in rural areas of Zacapa,
Guatemala.
Special thanks go to Erick Acevedo from the
village of San Juan for his collaboration during the
veterinary inspection. We thank Manuel Barrios
Izás from Centro Universitario de Zacapa (USAC)
features have been the size, number and
measurements of the rostellar hooks (Loos-Frank,
2000). Although the morphology of T. solium is
specifically known, new morphometric parameters
have been proposed and used for the description of
rostellar hooks in various species of the genus
Taenia (Haukisalmi et al., 2011). To enhance the
knowledge about the morphology of the rostellar
hooks of T. s o l i u m we have used nine
morphometric measurements. The results of our
study are similar to those reported by Verster
(1969) (Brazil and Poland), Boa et al. (1995)
(Tanzania) and Chawhan et al. (2014) (India)
concerning the total length of the small and large
hooks of the larval stage of T. solium; mean: 125-
171 µm (small/large); 120-169 µm; 118-159 µm,
respectively. Schmidt et al. (2015) reported three
parameters: total length (128-185 µm), width
(47.5-70 µm) and apical length (62.5-97.5µm).
Interestingly, all these measurements were similar
to the results we obtained from small hooks.
Whereas the large hooks we examined were
smaller for the three parameters. The blade
curvature length was described by Chawhan et al.
(2014) (mean: 65.6-89.3 µm), and our results differ
significantly; we found shorter blade curvatures of
small and large hooks. Nevertheless, in that study
the point that origin the curvature, between the
guard (distal part) and the blade, was not
considered as a reference point, and the origin was
taken into account from the medial part of the
guard. Thus, the differences are due to the use of
this inaccurate point of origin. The rest of the
morphometric parameters have not been
considered in any other study of T. solium.
However, it would be important to compare the
complete morphology of rostellar hooks from
specimens of different geographical regions,
continents and different genotypes to determine if
intraspecific morphological variation exists in
metacestodes and adult T. solium, as it has been
observed in T. hydatigena, another species that
parasitize domestic pigs (Filip et al., 2019).
The overlap of T. solium and T. hydatigena is more
common than it was thought, and various studies
have confirmed the presence of both species in
domestic pigs (Conlan et al., 2012; Chembensofu
et al., 2017; Chaisiri et al., 2018). Other studies
have reported T. solium metacestodes in the viscera
of pigs (Ostertag, 1913; Chembensofu et al., 2017).
Therefore, when sufficient metacestodes are
90
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