A Literature Survey of Common Parasitic Zoonoses
Encountered at Post-Mortem Examination in Slaughter
Stocks in Tanzania: Economic and Public Health
Implications Volume 1 - Issue 5
Erick VG Komba*
Department of Veterinary Medicine and Public Health, Sokoine University of Agriculture, Tanzania
Received: September 21, 2017; Published: October 06, 2017
Corresponding author: Erick VG Komba, Senior lecturer, Department of Veterinary Medicine and Public Health, College of Veterinary Medicine and
Biomedical Sciences, Sokoine University of Agriculture, P.O. Box 3021, Morogoro, Tanzania
Zoonoses caused by parasites constitute a large group of infectious diseases with varying host ranges and patterns of transmission. Their
distribution, prevalence and transmission patterns are affected by the influence of both human and environmental factors. The economic and
public health impact of such zoonoses warrants appropriate surveillance to obtain enough information that will provide inputs in the design
and implementation of control strategies. A need therefore arises to regularly re-evaluate the current status of zoonotic diseases, particularly
in view of new data available as a result of surveillance activities and the application of new technologies. Consequently this paper summarizes
available information in Tanzania on parasitic zoonoses encountered in slaughter stocks during post-mortem examination at slaughter facilities.
The occurrence, in slaughter stocks, of fasciola spp, Echinococcus granulosus (hydatid) cysts, Taenia saginata Cysts, Taenia solium Cysts and
ascaris spp. have been reported by various researchers. Information on these parasitic diseases is presented in this paper as they are the most
important ones encountered in slaughter stocks in the country.
Keywords: Parasitic Zoonoses; Slaughter Stocks; Post-Mortem Examination; Traditional Sector
Abbreviations: MAFS: Ministry of Agriculture and Food security; CE: Cystic Echinococcosis; NCC: Neurocysticercosis
In Tanzania slaughter stocks are mainly composed of cattle,
pigs, goats and sheep. Most of these are supplied to the slaughter
facilities by the rural based traditional livestock sector which
constitutes more than 98% of the total livestock population in
the country [1]. Apart from poor animal genetic makeup and poor
management, the traditional livestock sector suffers high disease
burden due to lack/inadequacy of veterinary services attributable
to shortage of veterinary staff, poor infrastructure especially
transport facilities and lack of diagnostic facilities and drugs [2-6].
As a result animals brought for slaughter into urban areas from the
rural traditional sector may harbor chronic or subclinical infections
some of which have zoonotic implication. Such diseases are rarely
detected during ante-mortem examination and hence infected
animals proceed into slaughter.
Zoonoses have been defined as diseases and infections that
are naturally transmitted between vertebrate animals and humans
[7,8]. They are among the most important animal and public health
problems that affect the well being of societies worldwide; and
yet most of them go unrecorded and are often neglected [9]. Most
zoonoses are maintained in the animal reservoir but can cross
over to humans as a result of different risk factors and behavioral
traits. Zoonoses caused by parasites have recently assumed an
important role in public health with some of them being involved
in opportunistic infections [10]. They are an important cause of
human parasitic diseases worldwide and a major threat to the
socio-economic development of especially developing countries
[11]. The migration of humans and their domestic animals has
been the pathway for disseminating parasitic zoonoses throughout
recorded history and will continue to have an impact on emergency,
frequency and spread of infections [12].
A slaughterhouse or abattoir refers to the premises approved
and registered by the controlling authority used in the slaughterof animals for human consumption [13]. For a long period
abattoirs have played an important role in the surveillance of
various diseases of human and animal health importance [14-
16]. Surveillance at the abattoir is known to allow for all animals
passing into the human food chain to be examined for unusual
signs, lesions or specific diseases. Abattoir data are useful as
they can provide a rough picture of emerging diseases [17]. As a
result this paper summarizes common zoonoses encountered in
slaughter stocks at abattoir during post-mortem meat inspection.
It focuses on those zoonotic parasites transmitted from animals
to humans. The described prevalence and distribution of various
parasitic zoonoses in this paper will help responsible public health
authorities in targeting of control measures and monitoring of the
progress of food-safety policies.
A literature search was conducted using the Pubmed database
which comprises citations for biomedical literature from Medline,
life science journals and online books. Various combinations of
the following terms were used: ‘Zoonotic parasites’, ‘Parasitic
infections’, ‘Zoonotic, Helminths’, and ‘Slaughterstocks’, ‘cattle’,
‘goats’, ‘sheep’, ‘pigs’, and ‘abattoir’, ‘slaughter facility’, ‘slaughter
house’, ‘postmortem inspection’, and ‘Tanzania’. Articles mentioned
in the reference lists of the initially obtained articles were also
screened to get additional articles. From the several articles
detailed review of the abstracts identified 14 most relevant and
representative studies of zoonotic parasitic infections encountered
in slaughter stocks in the country, and these were chosen for the
present paper.
Fasciolosis is a parasitic zoonosis caused by liver flukes,
Fasciola gigantica and F. hepatica, belonging to the genus fasciola
[18]. F. hepatica has been known to be the main causal agent as
it assumes a worldwide distribution [19]. In Tanzania the disease
has been reported to be among the major constraints to ruminant
production in different regions [20]. Though liver fluke infestation
rarely causes mortalities in cattle, much of the economic importance
of the disease is due to its effect on production and economic
losses owing to condemnations of the livers. Studies involving live
animals have reported high prevalence rates in traditional cattle
stocks in the country [20-22]. Abattoir surveys in the country
have found the disease to be the commonest and a leading cause
of liver condemnations in slaughter cattle [2,3,5,20,23,24]. A study
by Keyyu et al. [21] reported up to 100% liver condemnation rates
in some slaughter slabs in rural areas in Iringa region due to liver
flukes in cattle.
Reports also exist on detection of the disease in small
ruminants during post-mortem inspection [3,5], prevalence rates
ranging from 3.1% to 17.1% (Sheep) and 3.1% to 18.5% (Goats).
However, small ruminants suffer from an acute form of the disease
which is normally associated with high mortalities [25,26]. The
proportion contributions of fasciolosis to total liver condemnations
in the reported studies may not be a true reflection of infections
in slaughter stocks since there are many light infections in which
affected parts are trimmed and the remaining portion passed for
human consumption and these are not recorded [2,5,6]. Apart from
its importance in veterinary and economic terms, fasciolosis has
been shown to be a reemerging and widespread zoonosis affecting
a number of human populations throughout the world [27,28].
According to Mas Coma et al. [28] emergence/re-emergence of
the disease in many countries is an attribute of many phenomena
related to environmental changes and manmade modifications.
Together with other trematodiases the disease is included in a
list of important helminthiases with a great impact on human
development.
Cystic Echinococcosis /Hydatid Disease
Cystic Echinococcosis (CE) is a zoonotic disease caused by
larval stage of the tape worm, Echinococcus granulosus, whose
adult forms are seen in carnivores [29,30]. Ungulates and humans
act as intermediate hosts for the parasite with human infections
being caused by ingestion of the tapeworm eggs while playing with
infected dogs containing eggs in the fur or through consumption
of garden vegetables or water contaminated by dog feces [31]. The
organism assumes a cosmopolitan distribution but is endemic in
the Mediterranean, Africa, Middle East, South America, Aus¬tralia,
Russia, and China where livestock, mainly sheep and cattle, are
raised with dogs who harbor the adult phase of the tapeworm [29-
35]. Echinococcus granulosus causes serious lung and liver disease
[36-40] and less frequently affects the kidney, peritoneum, spleen
[31]. Maintanance and spread of the disease in endemic areas are
known to be influenced by the diversity of livestock production
systems, poor and unsupervised slaughter-houses, illegal and
family slaughtering, low public awareness of the disease, and a
large stray dog population [35].
Apart from exerting health effects to both humans and animals,
hydatid cysts have important economic consequences [41]. On the
human side economic losses arise through diagnostic cost, treatment
cost, hospitalization, convalescence, life impairment and fatal
outcomes. In animals economic losses are observed in decreased
carcass weight, milk production and fertility rates, and from
increased rate of condemnation of affected organs. In intermediate
hosts (ungulates), cysts of E. granulosus are usually detected bat
post-mortem abattoir examination of the viscera [42], providing
important epidemiological data, which can be used to define likely
Echinococcal infection pressure [43-45]. Abattoir based studies in
the country (Tanzania) have revealed that the disease is prevalent
among slaughter stocks particularly cattle [2,4-6,46,47] as well as
sheep and goats [4-6,48]. A study by Braae et al. [48] also detected
the parasites in 6.6% of the slaughter pigs they examined (n=243).
Some other studies reported occurrence of the disease in humans
more so in pastoral communities [49,50]. Studies elsewhere in
pastoralist communities in other African countries [51-60] and
other continents [61,62] also showed evidence of existence of the
disease in humans and domestic animals particularly cattle, sheep
and goats. Poor sanitation and hygiene, and unrestricted disposalof animal viscera post-slaughter may be responsible for the high
prevalence Echinococcosis.
Taenia saginata Cysticercosis
Taenia saginata is a two host parasite whose larval stage, known
as Cysticercus bovis, is found in cattle, and the adult tapeworm,
Taenia saginata, is found in intestines of man [63,64]. The cycle is
completed when eggs in gravid proglottids shed from the human
tapeworm are ingested by cattle, and viable cysts in undercooked
beef are consumed by man [63,65]. The public health and economic
consequences of infection of cattle with metacestodes of this
worldwide occurring human tapeworm are considerable [66].
In humans infected individuals may remain asymptomatic for
years, and the only symptom may be the spontaneous passage
of proglottids. However, non-specific symptoms, such as vague
abdominal pain, vomiting, nausea, diarrhea and weight loss can be
present [67]. Although the tapeworm seems to be a benign parasitic
disease, it can lead to serious surgical Gastrointestinal System (GIS)
complications that are seldom reported in the medical literature
[67-69]. In Tanzania a number of works have reported occurrence
of the parasite in slaughter cattle [2,4-6,47]. Though the prevalence
rates were fairly small (less than 2%) the implication thereof is
significant. Low prevalence rates of the parasite in slaughter cattle
have also been reported in other countries [70].
Taenia solium Cysticercosis
Porcine cysticercosis is a parasitic zoonosis caused by the larval
stage of a tapeworm Taenia solium [71]. The disease is endemic in
most developing countries of Latin America, Asia and sub-Saharan
Africa where pork is consumed causing serious public health and
agricultural consequences [72-76]. While pigs are the intermediate
hosts, man is the only natural definitive host. Pigs usually get
infected by eating infected human feces or by consuming feed or
water contaminated with human feces. Humans can also become
accidental intermediate hosts upon ingestion of T. solium eggs
[77,78]. In both humans and pigs, the larval stage of T. solium can
establish in the muscles and/or in the brain, the latter resulting
in Neurocysticercosis (NCC), which is the most common cause
of human acquired epilepsy in many developing countries and
accounts for over 20 million cases and 50 000 deaths each year
[73,79]. NCC is a neglected disease, and its prevalence is largely
underestimated [80]. Human NCC may lead to acute seizures,
epilepsy and other neurological manifestations [81]. Ingestion of
larvae (Cysticerci) present in raw or under-cooked pork may result
in human tapeworm infection.
In Tanzania several abattoir surveys have been conducted to
establish the existence of porcine Cysticercosis in slaughter pigs
[6,82-85]. Prevalence rates as high as 24.4% [83] have been reported
in slaughter pigs. The detection of the parasites in live animals has
also been attempted [83,85-88] revealing high prevalence of the
disease in rural communities where traditional pig husbandry is
practiced. Studies in slaughter and live animals in other countries in
the East and central African region have also found the disease to be
prevalent in the traditional pig husbandry [89-96]. Several studies
in endemic areas have associated the disease with free ranging pig
husbandry, poor sanitary practices and lack of veterinary control,
all related to poverty [77,86,97,98].
Ascariosis
Ascaris suum is a nematode found in pigs causing a disease
known as ascariosis [99]. Human infections with Ascaris suum
such as cases with larva migrans and eosinophilic pneumonia
have been reported [100-105]. In some molecular studies carried
out in some regions on human intestines, Ascaris suum infections
were determined to be prevalent [99]. Infections in humans and
other mammalians result from the ingestion of food and water
contaminated by A. suum eggs. Several studies have investigated
occurrence of ascariosis in slaughter pigs in Tanzania [6,84,86],
reporting different rates. A low rate of 4.03% was reported by
Mellau et al. [6] in a record based study in northern part of the
country whereas Ngowi et al. [86] reported the highest rate of
44.3% in a different location of the same part of the country. A
lower rate of ascariosis (4.1%) has been reported in Turkey [99]
whereas rates as higher as 54.5% and 36.7% have been reported
in Botswana [106] and in China [107]. According to Olson and
Guselle [103], 50% to 70% of pigs are estimated to be infected
by A. suum in the world. Differences in reported prevalence may
be attributable to limitations of abattoir records (record based
studies), pig management systems, diagnosis methods used [6]
and differences in levels of anthelmintic use among pig producers
[84]. The observed prevalence of the condition in slaughter pigs
in the country is of economic and public health importance due
to zoonotic nature of the disease [108]. Some further work is
however needed to establish factors responsible for transmission
and maintenance of ascariosis and to evaluate the implication of the
parasite in economic and public health terms.
Parasitic zoonoses are prevalent among livestock destined
for human consumption in Tanzania. Reported prevalence rates
of these conditions have enormous economic and public health
implications. As revealed by large quantities of condemned organs
and/or carcasses, post mortem meat inspection is playing an
outstanding role in safeguarding consumers’ health in Tanzania.
Sadly, such large quantities of condemned organs and/or carcasses
have a huge negative impact on the economy of farmers and the
country at large. Although the abattoir survey reports collated and
availed in this review are not juxtaposing true estimates of the
prevalence of parasitic zoonoses in Tanzania, they still provide good
overview of the trend and status of these zoonoses in the country;
and can therefore guide in planning future co-ordinated researches
and control programs.
ISSN: 2574 -1241
Abstract
PDF
