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A Review of Public Health Problems Associated with the Integration of Animal Husbandry and Aquaculture, with Emphasis on Southeast Asia

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Abstract

Although the recycling of excrements in integrated agriculture-aquaculture farming systems offers many advantages, the spread of diseases to man via aquatic organisms multiplying in excreta-laden water needs special attention. There is strong evidence that aquatic organisms may be more important vectors for human diseases than generally realized. However, conclusive epidemiological studies linking the use of excreta in aquaculture with human diseases are lacking.
Biological Wastes 31 (1990) 69-83
A Review of Public Health Problems Associated with the
Integration of Animal Husbandry and Aquaculture, with
Emphasis on Southeast Asia
Ludwig C. A. Naegel
Fanning Systems and Soil Resources Institute (FSSRI),
University of The Philippines at Los Bafios (UPLB),
College, Laguna-3720, The Philippines
(Received 23 February 1989; revised version received 20 April 1989;
accepted 16 May 1989)
ABSTRACT
Although the recycling of excrements in integrated agriculture-aquaculture
farming systems offers many advantages, the spread of diseases to man via
aquatic organisms multiplying in excreta-laden water needs special attention.
There is strong evidence that aquatic organisms may be more important
vectors for human diseases than generally realized. However, conclusive
epidemiological studies linking the use of excreta in aquaculture with human
diseases are lacking.
INTRODUCTION
In Southeast Asia aquaculture systems are popular; with the integration of
animal husbandry into such systems, a relatively new dimension on fish
production has emerged. This is in the field of public health.
Aquaculture, the production of aquatic organisms under controlled
conditions, and the methods of introducing organic wastes and excreta from
agricultural and human sources into pond systems, originated from China.
The use of organic wastes and excreta for aquaculture provides to the pond
system a free supply of organic fertilizer. Otherwise useless, waste products
are recycled into valuable fish feed; at the same time the environment
69
Biological Wastes 0269-7483/90/$03'50 © 1990 Elsevier Science Publishers Ltd, England.
Printed in Great Britain
70
Ludwig C. A. Naegel
receives less pollutants; and by including a biogas digester into the
integrated system, it is possible to obtain additional energy from wastes.
In China there is no such thing as waste--waste is only a misplaced
resource which can become valuable for another product (FAO, 1977;
Taiganides, 1978). Edwards (1985a) states that 'without excreta recycling, the
Chinese might not be able to maintain their agriculture production'.
In January 1978, the first international conference on the integration of
fish farming and waste disposal took place in London and more than 80
scientists participated (Pastakia, 1978). Reviews were published by
Wohlfarth and Schroeder (1979), and by Edwards (1980) about the recycling
of organic wastes into fish. The Asian experiences with the integrated crop-
livestock fish farming systems were discussed in detail in May 1980 in Taipei,
Taiwan (FFTC, 1980), and on a larger regional basis in August 1980 at the
ICLARM-SEARCA Conference in Manila (Pullin & Shehadeh, 1980).
Since then, a large number of publications on this topic has appeared: for
example, literature about the integration of pig and fish farming (Edwards,
1985b; Tamse
et al.,
1985), about the utilization of duck and poultry
droppings in fish farming (Barash
et al.,
1982; Edwards
et al.,
1983; Plavnik
et al.,
1983), about the use of cow manure in fish production (Degani
et al.,
1984), and even on the use of rabbit droppings for biogas and fish production
(Mahadevaswamy & Venkataraman, 1988).
The main reason for adding animal manures to fish ponds is to provide
degradable organic matter, which is the most important component to
promote the growth of bacteria and zooplankton. During the decompo-
sition of the bacteria, CO2, phosphorus, nitrogen and other nutrients are
liberated to form essential constituents for phytoplankton and algal growth
(Schroeder, 1980). Phyto- and zooplankton form the base of the food
chain for fish and other aquatic organisms. A part of the added excreta can
also serve as direct feed for several cultivated fish species like tilapia, mullet
and carp.
In view of the rising costs worldwide for chemical fertilizers and for
supplemental feed for aquaculture, the use of excreta from domestic animals
and also from man is gaining more and more importance for the fertilization
of ponds. This is especially true in tropical countries, where several
important fish species are cultured, which are primary consumers and low in
the food chain, like tilapia, Chinese carp species, the common carp, the
milkfish
(Chanos chanos)
and mullet
(Mugil
spp.).
However, the use of excreta from domestic animals and from man has two
sides. On one hand, excreta provide an inexpensive source of nutrients to
promote zoo- and phytoplankton growth. On the other hand, manures
contain a wide variety of bacterial, viral, protozoal and helminth pathogens
which may be transmitted via aquatic organisms to man and thus present a
Health problems in integrated agriculture-aquaculture farming 71
public health hazard. Where excreta are used in aquaculture, three groups of
people may be at a risk of infection:
(a) Persons who consume raw or insufficiently cooked aquatic
organisms. Adding lemon juice, garlic and onions to raw, infected
fish does not destroy pathogens, contrary to common belief. The
same is true with pickling or fermenting raw fish.
(b) Persons who consume raw or inadequately cooked meat of animals
that have been fed with raw, infected fish or contaminated plants.
(c) Persons with occupational exposure to ponds laden with excreta, and
people handling and preparing contaminated aquatic products.
Reichenbach-Klinke and Elkan (1965) briefly discussed the possibility of
fish as carriers of organisms that can cause human disease, and the public
health aspects related to warm water pond aquaculture causing consumer
and non-consumer-related diseases were considered by Brock (1983). In a
study on the health constraints from integrated animal-fish farming in the
Philippines, several examples were described; however, this was mainly from
a taxonomic point of view (Velasquez, 1980).
The degree of risk of infection varies considerably with the type of
pathogen, and before an outbreak of an illness can manifest, a chain of
events must occur. Whether or not an infective dose of pathogen reaches a
human depends on the following:
(a) The concentration of pathogens in the manure, the time between the
excretion and infection, the die-off rate of the pathogen in the new
environment and the ability to multiply there.
(b) Many pathogens require one or even two intermediate hosts before
becoming a threat for man.
(c) The practices of food handling and preparation, level of sanitation,
and food consumption habits all have a significant influence on the
risk of infection from diseases.
(d) The pattern of human immunity determines finally whether or not an
outbreak of illness occurs.
Alternative routes of transmission of the pathogen have to be considered,
which further obscure the steps between the presence of pathogens in
excreta and the determinable human infection attributable to the intro-
duction of excreta in aquaculture (Blum & Feachem, 1985). This rather
complex situation is one reason why until today only a very limited number
of epidemiological studies have focused attention on the public health risks
associated with the introduction of excreta in aquaculture.
It is important to point out that enormous differences of opinion exist
between epidemiologists and aquaculturists. The epidemiologists treat
72 Ludwig C. A. Naegel
animal wastes as a reservoir of pathogenic organisms dangerous to animals
and/or man. The aquaculturists, in contrast, know that in nature inter- and
mono-species coprophagy always exists, that aquatic organisms are always
in close contact with their own excrements, and that the conventional fish
feeds are not always free of pathogens (Mueller, 1980).
Additionally, in the large number of scientific studies which deal with the
recycling of excreta for fish farming, only healthy animals have been used.
For this reason, it is not surprising that in these studies no threat to the
health of man by the use of excreta in aquaculture could be found.
On the other hand, there is a lack of studies which deal with the excreta
from animals raised by poor farmers who often cannot affort the prevention
and control of infectious and parasitic diseases in their animals.
IMPORTANT PATHOGENS ASSOCIATED WITH THE
OUTBREAK OF DISEASES DUE TO THE INTRODUCTION OF
EXCRETA IN AQUACULTURE SYSTEMS
In the following pages are described the most important pathogens which
can be linked to public health problems caused by the introduction of
excreta in aquaculture. These diseases are endemic not only in Southeast
Asia, but also in many other tropical countries. However, the prevalence
patterns vary across regions and continents, between rural and urban areas,
and with climatic zones. Aquacultural practices, eating habits, cultural
norms, and social environments are important factors determining the
prevalence pattern and rendering particular diseases typical of a given
community or area (Cross, 1985).
In this review, the focus is on The Philippines situation; however, studies
from other countries are included where relevant to the topic.
After excretion and release into the external environment, eventually all
pathogens will die or lose infectivity. In general, the reduction of viable
pathogens is exponential, i.e. there is a rapid decrease in the numbers in the
first few hours or days after excretion, with a reduced number surviving over
an extended period. Variations of this die-off pattern are found in a few
bacteria (e.g. Salmonella) which may temporarily multiply outside the host,
and with helminths which have one or more non-infective intermediate
development stages with typical die-offpatterns. A further variation is found
with trematodes, which have a multiplication phase in intermediate hosts
(Cross et al., 1985). Environmental factors like temperature, moisture
content, nutrients, sunlight, predators and competition by other micro-
organisms determine the actual die-off rate and the number of organisms
surviving within a given time period (Strauss, 1985).
Health problems in integrated agriculture-aquaculture farming
73
Enteric bacteria and viruses
In the following table are listed the most important infectious microbial and
protozoal pathogens with a potential for spread of diseases by the
introduction of excreta in aquaculture (Table 1).
From this table, it becomes very clear that the most frequent illness is
diarrhoea, and that no intermediate host is involved during transmission.
It is generally accepted that human and warm-blooded animal bacterial
and viral pathogens do not cause acute diseases in aquatic organisms.
Aquatic organisms can be considered passive carriers and mechanical
transmitters of pathogens to man without the involvement of an
intermediate host (Janssen, 1970). Fish grown in excreta-laden ponds carry
these pathogens only passively in their intestines, gills and in the mucus of
their skin. Tissue and blood from infected fish have appeared to be sterile
(Nupen, 1983; Cloete
et al.,
1984). In recent studies, however, it has been
proven that after exceeding a rather clearly defined threshold concentration
of pathogens in the water, both viruses and bacteria are able to penetrate
into the peritoneal fluid and even into the muscles of fish (Buras
et aL,
1985;
Buras
et al.,
1986; Buras
et aL,
1987). This has an impact on the transmission
of viruses and bacteria to persons who have direct contact with the
intraperitoneal fluid and blood of infected fish, like fishhandlers and
housewives when they are cutting, gutting and cleaning fish in preparation
TABLE 1
Important Infectious Pathogens with Potential for Spread by the use of Excreta in
Aquaculture (after Blum & Feachem, 1985)
Pathogens Diseases Intermediate host
Viruses
Enteroviruses
Hepatitis A
Rotavirus
Bacteria
Campylobacter jejuni
Path.
E. coli
Salmonella
spp.
Salmonella typhimurium
Shigella
spp.
Vibrio cholerae
Protozoa
Entamoeba histolytica
Giardia lamblia
Poliomyelitis, meningitis,
fever, diarrhoea None
Infectious hepatitis None
Diarrhoea None
Diarrhoea, vomiting None
Diarrhoea, dysentery None
Diarrhoea, dysentery None
Typhoid fever None
Diarrhoea, dysentery None
Cholera, diarrhoea None
Diarrhoea, dysentery None
Diarrhoea None
74
Ludwig C. A. Naegel
for consumption. Viruses are immediately infective upon release into the
environment and the minimal infective dose is usually low; it is believed that
even a single virus may confer an infection if circumstances are suitable
(Cross, 1985). Although the concentration of viruses and bacteria added
with the excrements into the aquaculture system is reduced drastically by
dilution, filter feeders like milkfish, mullet and tilapia can concentrate these
pathogens and by this, despite the die-off pattern and high dilution in the
water, can create a possible health hazard.
Enteric viruses and bacteria can survive for long periods in fresh and sea
water. Viable
Salmonella typhimurium
could be isolated from the viscera and
epithelium of tilapia, and from water in pools more than 16 days after
inoculation (Baker
et al.,
1983). Some human pathogens multiply in the gut,
mucus and tissue of fishes. A marine bacterium and one of the most
troublesome enteric pathogens in Japan,
Vibrio parahaemolyticus,
is thought
to be such a pathogen (Janssen, 1970).
In the Philippines, several studies have been conducted on such
pathogens. Accordingly,
I1. parahaemolyticus
could be isolated in high
numbers from milkfish (Jacalne
et al.,
1975). Prevalence of Salmonella in
milkfish reared in brackish water ponds, was clearly associated with the
fertilization of the ponds with untreated chicken manure (Manlapig, 1981).
The application of untreated chicken manure to fertilize shrimp ponds
significantly increased
Vibrio parahaemolyticus
and Salmonella in cultured
shrimps, leading to problems of marketing the product to industrialized
countries (Reilly
et al.,
1982).
A study in Israel on the health risks arising from the practice of using
wastewater for fish culture in ponds, and the use of water from fish ponds for
agricultural irrigation, revealed a higher rate of clinical enteric diseases in
villages re-using wastewater than in other villages
(Fattal,
1983).
In most bacterial and viral illnesses, it is very difficult to determine the
exact species of pathogen without a laboratory examination, since the
pathological manifestations of most enteric bacterial and viral diseases are
very similar--diarrhoea.
Caution, however, has to be taken in this instance. In countries like the
Philippines where diarrhoea is a major health problem, the official health
statistics are incomplete and do not differentiate between the microbial
species of pathogens, mainly due to a lack of laboratory facilities. Therefore,
the data presented have to be taken with great care.
Convincing epidemiological studies have still to be carried out to link the
risk of bacterial, viral or protozoal infections to consumption of aquatic
organisms produced in excreta-laden ponds. Experimental studies suggest
that there might be strong links between the recurrence of influenza A virus
epidemics and the integration of aquaculture with duck and pig farming
Health problems in integrated agriculture-aquaculture farming
75
close to human dwellings. Human influenza viruses can multiply in ducks,
but the avian viruses are not transmitted to man. However, the transmission
of genetic material from ducks to human influenza viruses appears to take
place by reassortment in pigs. Pigs can become infected by and may transmit
both human and avian influenza viruses not only amongst other pigs but
also to the original host. Therefore, pigs seem to be 'mixing vessels' where
two separate genetic reservoirs meet and where reassortment between avian
and human influenza A viruses occurs, giving rise to an antigenic shift by
creating new human influenza strains with new surface antigens. For this
reason Scholtissek and Naylor (1988), recommend the development of
integrated aquaculture systems where pigs are kept in enclosed farms
separate from ducks.
Infectious protozoa
It is well known that
Entamoeba histolytica
can be transmitted to man
through the recycling of infected manure from domestic animals and from
infected night-soil used as fertilizer in ponds for the production offish and of
macrophytes. The live cysts can reach man or domestic animals with the
consumption of contaminated plants and fresh or inadequately cooked fish.
The cyst wall breaks up and trophozoites develop and invade the intestinal
mucosa and other tissues of the host. Cyst formation follows with the
dehydration of the fecal matter as it moves down the colon.
Amoebiasis is widely distributed in countries where excreta are used as
fertilizer for fish ponds. Surveys in The Philippines show a prevalence from
3 to 14% of the human population. In this country the main reason for
infections with amoeba are poor sanitary disposal systems for human
excreta, and inadequate provisions for safe water supplies (Institute of
Public Health, UP Manila, pers. comm., 1988). The very common use of
untreated manures as fertilizer in fish ponds can add to the number of
incidence of amoebiasis.
Heiminths (Trematodes)
There are numerous infectious helminths which can be transmitted to man.
Perhaps due to the widespread application of excreta in aquaculture systems
in the Far East and in Southeast Asia, most incidences are reported from this
region. This points out the need for special precautions to be taken to
prevent the spread of helminth diseases with the introduction of manures in
aquaculture in other regions. In this respect the often indiscriminate
introduction of non-indigenous fish species without prior precautionary
76 Ludwig C. A. Naegel
TABLE 2
Important Trematodes with a Potential for Spread
Aquaculture by the Recycling of Excreta in
Pathogen 1 and 2 Intermediate hosts Final hosts
Clonorchis sinensis
(Chinese liver fluke)
Echinostoma ilocanum
(Garrison's fluke)
Fasciola hepatica
(Liver fluke)
Heterophyes heterophyes
(yon Siebold's fluke)
Metagonimus yokogawai
Fasciolepsis buski
(Intestinal fluke)
Opisthorchis felineus
Paragonimus westermani
(Oriental fluke)
Schistosoma spp.
Freshwater snail--
Cyprinidae
Freshwater snail
( Pila luzonica)
Amphibious snail--
aquatic plants
Freshwater snail--
Mullet, tilapia, catfish
Freshwater snail--
Salmonids, Cyprinids
Freshwater snail--
aquatic plants
Freshwater snail
Cyprinids, tilapia
Freshwater snail
Crayfish, crab
Freshwater snail
(Hepato-intestinal/
urinary schistosomiasis/
bilharziosis)
Man, cat, dog
Man, dog, rat
Man, pig, cattle
Man
Man
Man, pig, cattle
Man, cat, dog, pig "
Man, cat, dog, rat
Man, cat, dog, rat
goat, dog
measures of quarantine can cause the spread of helminth diseases to new
areas.
The life cycle of helminths includes one or two intermediate hosts. This
fact reduces the potential for transmission. If however, the appropriate host
or hosts are present in the water the potential for spread increases
significantly, since the larval stages of the trematodes (flukes) multiply in the
host. Transmission to man can only occur if appropriate host/hosts are
present and if man consumes either raw or partially cooked flesh from the
intermediate host which contains the helminthic larva.
The most common trematodes which can be transmitted through the
introduction of excreta in aquaculture, and which pose potential health
hazards for man, are briefly described below (Table 2). Note the first and
intermediate and the final hosts. A detailed description of their often
complex life cycles can be found in standard textbooks of parasitology.
Health problems in integrated agriculture-aquaculture farming
77
Eggs of
Clonorchis sinensis
(Chinese liver fluke),
Opisthorchis viverrini
and
O. felineus
are excreted by man, pig, cat and dog and are transmitted via
freshwater snails as their first intermediate host, and via freshwater fish as
their second intermediate host. The consumption of raw or insufficiently
cooked infected fish can cause clonorchiasis and opistorchiasis (McGarry,
1977).
With the construction of irrigation canals for rice production, and the
cultivation of tilapia in excreta-laden water, the incidences of opisthor-
chiasis have reached an alarming dimension in Thailand. This is attributable
to the consumption of raw tilapia infected with O.
viverrini.
In man the eggs
of O.
viverrini
are not excreted but they are responsible for painful immune
reactions, which can eventually lead to liver cirrhosis and death (Merkle, A.,
GTZ, Eschborn, FRG, pers. comm., 1986).
In the northern parts of the Philippines, infections with the intestinal fluke
Echinostoma ilocanum
(Garrison's fluke) are common. In endemic areas
about 5% of the population suffer from this parasite. The infection can be
traced to the consumption of raw or inadequately cooked freshwater snails
grown in excreta-laden ponds. In some parts of the country, freshwater
snails are considered to be a delicacy. Feeding aquatic macrophytes,
which are contaminated with infected snails, to hogs and cattle and the
recycling of their manure in ponds increases the incidence of infection with
Garrisons's fluke.
In Asia the common trematodes affecting man, pig and cattle are
Fasciola
hepatica,
the cattle or sheep liver fluke, and
Fasciolepsis buski
(giant
intestinal fluke). These are transmitted by the use of infected manures of
cattle, sheep and man, as fertilizer for fish ponds, via freshwater snails as
their first intermediate host and the consumption of raw or inadequately
cooked aquatic vegetation. Encysted and developed metacercaria of the
trematodes are found on the roots, on the fruits and leaves of macrophytes,
like the water chestnut
(Eliocharis tuberosa),
water spinach
(Ipomoea reptans)
or the water caltrop
(Tropa bicornis).
With the consumption of the raw or
uncooked infected plants, the metacercaria hatch in the duodenum of the
final host. In the Philippines the incidence of human infection with
Fasciola
spp. and
Fasciolepsis
spp. is low, since all aquatic plants for human
consumption are normally well-cooked; however, most water buffalos are
infected and present an important reservoir for this fluke disease.
The consumption of raw mullet, tilapia, milkfish, or catfish
(Clarius
batrachus)
can cause infections with
Heterophyes heterophyes
(von Siebold's
fluke), and the consumption of raw freshwater salmonids and cyprinids are
responsible for infections with
Metagonimus yokagawai.
Freshwater snails
serve as the first intermediate host of these two species of flukes
78 Ludwig, C. A. Naegel
(Reichenback-Klinke et al., 1965). In the southern part of The Philippines,
infections with the Oriental lung fluke (Paragonimus wastermani) are
common. When rice fields for integrated rice-fish production are fertilized
with infected human excrements, carnivorous animals or pigs, the eggs of the
fluke can find their first intermediate host in a freshwater snail (Brotia
asperata). The developed cercaria find their second host in a freshwater crab
(Sundathelphusaphilippina) where they encyst as metacercaria. Infection can
then easily follow, since crabs and crayfish grilled at open fires during parties
and only partly cooked meat sucked out from the shell are considered in the
Philippines as delicacies. Once in the human host, the worms hatch in the
duodenum and the young flukes penetrate the intestinal wall and finally
enter the lungs. Although the eggs of the lung flukes are coughed up with the
sputum, and in most cases are expectorated, they are also sometimes
swallowed. Swallowed eggs are found in the feces of man and pig, and
through the recycling of these infested excrements in aquaculture, another
life cycle of the lung fluke can start again.
All the above-described trematodes can only be transmitted to man and
other warm-blooded animals by the consumption of raw or insufficiently
cooked fish, crabs, or aquatic plants. However, the transmission of the
Schistosoma trematodes (Schistosomajaponicum or blood fluke, S. mansoni
or hepato-intestinal fluke, S. haematobium Bilharziose or urinary fluke) is an
occupational risk for persons working in ponds fertilized with untreated
infected excreta. Eggs of the Schistosoma fluke are transmitted with the
excreta of man and/or domestic animals to a freshwater snail. The infective
cercaria swim in the water until they come in contact with man or domestic
animals. They penetrate the skin and enter the circulatory system where they
become adults in 24 h and start to lay eggs. Not only man is infected by
Schistosoma, but also cattle, dogs and even goats, when coming into contact
with infested water. In The Philippines alone about 700000 people are
suffering from schistosomiasis (S. japonicum), mainly the aquaculture
workers and rice field farmers. The use of infected excrements of domestic
animals for fertilizing the fish ponds is one of the suspected basic causes.
To control schistosomiasis, a number of measures has to be implemented.
There should be avoidance of the introduction of infected excreta in
aquaculture; there should be snail control by biological means, for example
through the introduction of snail-eating fish species, and control through
chemical and water management techniques (De Bont & de Bont Hers, 1952;
Michelson, 1957; Malek, 1984). The giant Malaysian prawn, Macrobrachium
rosenbergii, is a predator for schistosome vector snails in fish ponds and can
act in this way as a biological control for the spread of schistosomiasis in
aquaculture (Lee et al., 1982).
Health problems in integrated agriculture-aquaculture farming
79
CONCLUSIONS
In Southeast Asia, as in other regions, the integration of animal husbandry
and the recycling of animal manures as a nutrient source in aquaculture offer
many benefits. However, because of the widespread use of untreated excreta,
the spread of a large number of viral, bacterial, protozoal and helminthic
diseases may be compounding public health problems.
Special attention has to be directed to the health aspects to avoid the
spread of diseases. There are several methods of minimizing the health
hazards:
1. The use of pathogen-free excreta. Unfortunately, complete destruction
of pathogens through the methods of waste treatment before applying
excreta to fish ponds is, from economic and technical points of view, not easy
to achieve, the anaerobic treatment of excreta in biogas digesters, often
thought to result in a pathogen-free effluent, today seems to be insufficient to
decrease the concentration of pathogens to safe levels, due to the too-short
detention time in the digesters (Feachem et al., 1981). The only process that
can produce a largely pathogen-free material is aerobic composting, a
method widely applied in China (Edwards, 1985a).
2. Control of spread of pathogens through veterinary activities and through
health education. To reduce the risk of infections through the recycling of
manures from domestic animals, special care has to be directed to the health
of the animals to prevent them from becoming a reservoir for human
pathogens.
Recycling of manures from healthy animals is leading to aquatic products
free from microbial pathogens and human parasites (Hopkins & Cruz, 1982;
Rice et aL, 1984). Through public health education, preventive medicine and
medical treatment of illnesses, the spread of infections can be reduced.
3. Pond management. The clearing of vegetation from pond banks can
help to control snails, which are the intermediate hosts for many pathogenic
helminths, expecially Clonorchis and Schistosoma.
4. Lengthening of the food chain. Although the use of untreated manures
and night-soil is a common practice, excrements should be added to
aquaculture systems with prior storage for at least two weeks to destroy the
eggs of trematodes. If possible, the aquatic product should not be used for
human consumption, but processed and used as animal feed. The
lengthening of the food chain can be considered as an additional safeguard
to public health. This is important in view of the fact that many fish species
tend to consume excreta directly and by this might accumulate and
incorporate bacterial and viral pathogens not only in the intestines, but also
in the intraperitoneal fluid and in the muscles.
80 Ludwig C. A. Naegel
5. Depuration of aquatic organisms before harvesting. If fish and other
aquatic organisms are produced for human consumption in excreta-recycle
systems, then at least prior to harvesting and marketing, the organisms
should be allowed to depurate for several weeks in clean water. This method
is widely applied in China and Vietnam, and in view of the results with fish
which show the incorporation of microbial pathogens even into muscles,
depuration is a very important step to minimize possible health hazards
from the use of excreta in aquaculture.
6. Handling and processing of aquatic products. The importance of good
hygienic conditions should be stressed at all stages of fish handling and
processing.
7. Consumption of raw aquatic products discouraged. As one of the most
important possibilities to minimize the health hazards from the introduction
of excreta in aquaculture systems, the consumption of raw or inadequately-
cooked aquatic products should be strongly discouraged. Through the
cooking of infected aquatic organisms, all pathogens can be destroyed.
ACKNOWLEDGEMENTS
This work would not have been possible without the many discussions with
faculty members of the Institute of Public Health, UP Manila, and without
the help from many colleagues in providing me with bibliographic
references. In the editing of this article, Mr Frank Hilario has been very
helpful. The author thanks them all and fully appreciates their friendly
cooperation.
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... There is strong evidence that aquatic organisms may be more important vectors for human diseases than generally realized. However, conclusive epidemiological studies linking the use of excreta in aquaculture with human diseases are lacking (Naegel, 1990). Great portion of the huge increase in China's recent inland aquaculture production is attributed to organic fertilization, provided by the parallel spectacular growth of poultry and pig production. ...
... mullet, shrimps, crayfish and snails) can concentrate these pathogens in its body fluids / surface. Despite the die-off pattern associated with this condition and high dilution in the water, they can propose a possible health hazard (Naegel, 1990). Author has also emphasized that convincing epidemiological studies still have to be done to link the risk of bacterial/viral infections to the consumption of aquatic organisms produced in manure-laden ponds. ...
... There is strong evidence that aquatic organisms may be more important vectors for human diseases than generally realized. However, conclusive epidemiological studies linking the use of excreta in aquaculture with human diseases are lacking (Naegel, 1990). Great portion of the huge increase in China's recent inland aquaculture production is attributed to organic fertilization, provided by the parallel spectacular growth of poultry and pig production. ...
... mullet, shrimps, crayfish and snails) can concentrate these pathogens in its body fluids / surface. Despite the die-off pattern associated with this condition and high dilution in the water, they can propose a possible health hazard (Naegel, 1990). Author has also emphasized that convincing epidemiological studies still have to be done to link the risk of bacterial/viral infections to the consumption of aquatic organisms produced in manure-laden ponds. ...
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... The WHO report on foodborne trematode infections (WHO 1995) suggests a link between excreta reuse in aquaculture and trematode infections but does not provide any specific information or data. Naegel (1990), in a review of health problems relating to the use of animal excreta in aquaculture, writes that there is potential for the spread of trematodes by such practices but does not provide any examples. Cross (1984) attributed an increase in the incidence of clonorchiasis in Hong Kong to the importation of pond-reared fish from China. ...
... 994;). However, none of these explicitly state that the parasites have been found in farmed fish or shellfish, although an association between disease and aquacultural practices is sometimes made. The WHO report on foodborne trematode infections (WHO, 1995) makes the link on more than one occasion in the text without providing any examples or data. Naegel (1990), in a review of health problems relating to the use of animal excreta in aquaculture, writes that there is potential for spread of trematodes by such practices but does not give any examples. Cross (1984) attributed an increase in the incidence of clonorchiasis in Hong Kong to the importation of pond-reared fish from China. Chen (1991) ...
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A retrospective epidemiological study was carried out on the association between enteric disease incidence and wastewater utilization in agriculture in 79 kibbutzim (cooperative agricultural settlements) in Israel. Medical records on disease incidence were collected directly from the patient files at the clinic of each kibbutz while environmental data was obtained from a detailed questionnaire. The kibbutzim included in the study were divided into four categories: I. thirty irrigating with wastewater effluent (population: 13,531), II. twenty-eight not utilizing effluent for any purpose (population: 11,096), III. ten using wastewater effluent as feed-water for fish ponds (population: 5,005), and IV. eleven which practiced two consecutive years of effluent utilization and another two consecutive years in which no effluent was utilized for any purpose or vice versa (population: 3,040). The findings reported herein are part of a major research project to be published elsewhere.** The project is designed to determine the association between enteric disease and wastewater utilization in agriculture. The full study utilizes a regression type of analysis based on logistic and log linear models designed to control for the numerous confounding factors. In this portion of the study, no excess in crude rates of viral hepatitis was found in effluent utilizing kibbutzim (categories I and III) when compared to non-effluent utilizing kibbutzim (category II). A significant (P<0.1) excess of shigellosis was found in all ages in effluent irrigating kibbutzim (I) (during the irrigation period), while a significant (P<0.01) excess of salmonellosis was found in kibbutzim using effluent as feed-water for fish ponds (III). *Although the research described in this article has been funded by the United States Environmental Protection Agency under Grant R-805174 to the Hebrew University of Jerusalem, it has not been subjected to the Agency's Peer and Policy Review and it does not necessarily reflect the views of the Agency and no official endorsement should be inferred. **Forthcoming E.P.A. reports.
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In 1977 and 1978, two fish ponds at the Dor Aquaculture Experiment Station were integrated with duck production. Each pond's area was 400 m2 and they were stocked with a polyculture of common carp, Tilapia, silver carp and grass carp (White Amur). The ducks were fed with prepared, nutritionally balanced feed, while the fish had to get by with the ducks' droppings plus the feed dropped directly from the ducks' beaks into the ponds. The ducks' performance on the ponds was superior to their ‘land’ control in growth rate, feed efficiency, viability and cleanness of feathers and skin. The average daily gain of the fish was 38.5 kg ha−1, not significantly different from ponds receiving similar mixtures of dry poultry manure plus supplementary feeds.Our experimental results provide necessary empirical support to the conclusion that the system is very efficient and its use should be expanded in warm water aquaculture.
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Tilapia aurea fry were stocked in five 0.05 ha ponds at 8000 fish/ha during June 1977. Four ponds received the wastes from 500, 1000, 2000 and 4000 laying hens/ha, respectively, while the fifth pond received no poultry wastes.After a 150-day growing period, final mean fish weights and average daily production paralleled the rates of organic fertilization. T. aurea averaged only 46 g in the pond which received no organic fertilization, but reached an average of 304 g in the pond fertilized by the wastes from 4000 hens/ha. Thus, T. aurea can be reared to market-size in Texas within a single growing season if sufficient levels of nutrient are available.Survival reached or exceeded 95% in all five ponds. Water quality remained within acceptable limits throughout the experiment, although the effects of organic fertilization on water quality were apparent.
Article
Tilapia, common carp and silver carp were reared in treated domestic wastewater. The most sensitive to this environment was the silver carp, followed by common carp and tilapia. In healthy clean fish, bacteria were not found in the blood or the muscles. They were present in small numbers in various organs and in concentrations of 106–107 g−1 in the digestive tract content. In fish exposed to treated wastewater for the entire growing period, bacteria were found in the muscles. The number of bacteria recovered from various organs ranged between 104–106 g−1 and their concentration in the digestive tract content was 108–109 g−1. The number of bacteria in the pond water determined the presence and concentration of bacteria in the fish. The number of bacteria that caused their appearance in the muscles of fish has been named the “threshold concentration”. Considering the public health aspects, fish can be reared in treated wastewater provided the bacteriological quality of the water is compatible with the “threshold concentration” levels of the fish grown in the ponds. The suitability of E. coli (fecal coliform bacteria) as indicators for the bacteriological quality of fish grown in wastewater-fed ponds is examined.
Article
Four species of carp and the Malaysian prawn grown in aquaculture ponds receiving swine manure were sampled throughout the growing season to determine levels of potentially pathogenic bacteria and human parasites. Water, swine manure, and sediments were also sampled routinely. The swine were fed antibiotic-free rations. Although the swine parasites Ascaris and Trichuris were present in hog manure, pond water, and sediments, no human parasites were found in the digestive tracts or tissues of necropsied fish or prawns. Several pathogenic and indicator bacteria present in swine manure were cultured using enrichment techniques, but these bacteria were cultured only rarely from water, sediments, or fish samples. Ponds enriched with swine manure generally supported more pathogenic bacteria, as well as more total bacteria. Aeromonas hydrophila, Pseudomonas sp., Corynebacterium sp., and several Enterobacteriaceae were isolated in relatively low numbers from scales of fish grown in swine manures. Since relatively low numbers of pathogenic bacteria and human parasites were observed on these carp and prawns, potential infections of processors or consumers will be reduced by proper handling and processing of aquaculture components which are grown in the presence of animal wastes.