(Part 12, Environmental Hygiene, VPE)
Topic: Stray and fallen animal management and Carcass Disposal. Vector and Reservoir Control.
Vector and Reservoir Control. Stray and fallen animal management and Carcass Disposal.
by Dr. Chanchal Debnath, Department of VPE, F/O-VAS, of WBUAFS.
Disease Reservoir
The reservoir is defined as any person, animal, arthropod, plant, soil, or substance, or a
combination of these, in which an infectious agent normally lives and multiplies, on which it
depends primarily for survival, and where it reproduces itself in such a manner that it can be
transmitted to a susceptible host. Simply, it is the natural habitat of the infectious agent in which
it metabolizes and replicates.
The terms reservoir and source are not always synonymous. For example, in hookworm
infection, the reservoir is man, but the source of infection is the soil contaminated with infective
larvae. In tetanus; the reservoir and source are the same that is soil. In typhoid fever, the
reservoir of infection may be a case or carrier, but the source of infection may be feces or urine
of patients or contaminated food, milk or water. Thus the term “source” refers to the immediate
source of infection and may or may not be a part of the reservoir
Types of Reservoir
The reservoir of infection may be of three types:
- Human reservoir
- Animal reservoir, and
- Reservoir in non-living things.
Human Reservoir: By far the most important source or reservoir of infection for humans is the man himself. He may
be a case or carrier.
Animal Reservoir: The source of infection may sometimes be animals and birds. These, like the
human sources of infection, maybe cases or carriers. The diseases and infections which are
transmissible to man from vertebrates are called zoonoses. There are enormous zoonotic diseases
which may be conveyed to man from animals and birds. The best-known examples are rabies,
yellow fever and influenza. The role of pigs and ducks in the spread of epidemic and pandemic
influenza both as reservoirs, carriers and “amplifying hosts” is now well established. The
migrations and movements of animals and birds may carry serious epizootiological and
epidemiological risks. There is evidence that genetic recombination between animal and human
viruses might produce “new” strains of viruses (e.g., influenza viruses).
Reservoir in Non-living things: Soil and inanimate matter can also act as reservoirs of
infection. For example, the soil may harbour agents that cause tetanus, anthrax,
coccidioidomycosis, and mycetoma.
Vector Control
Vector Is an insect or any animal that transmits a disease to other animals or humans. Eg.
Mosquitoes, tsetse, ticks, lice, fleas, etc.
Vector control is any method to limit or eradicate the mammals, birds, insects or other arthropods (here collectively called "vectors") which transmit disease pathogens. The most frequent type of vector control is mosquito control using a variety of strategies. Several of the "neglected tropical diseases" are spread by such vectors.
Vector-borne infections, diseases caused by pathogens transmitted by insects and ticks, have
long impacted human affairs. The Black Death, killer of tens of millions worldwide is the work
of a tiny flea vectoring the bacilli that cause bubonic plague from rats to people. Vector-borne
infections today is responsible for filling the hospitals of sub-Saharan Africa, Asia with malaria
victims suppressing the economies of nations and interrupting industrial operations where it
remains endemic. The disease can reach epidemic form very quickly. When vector control for a
particular disease is not in place then you need to improve, awareness, diagnostic facilities and
treatment of the disease to avoid any disaster.
Types of Vector
Mechanical vectors – Transmit pathogens by transporting them on their feet or mouthparts. Eg.
Housefly
Biological vectors – These vectors are involved in the life-cycle of parasite / arbovirus which must pass through the vector in order to mature to an effective stage capable of being transmitted to human or animal host when a vector takes a blood meal.
Importance of Vector Control
For diseases where there is no effective cure, such as Zika virus, West Nile fever and Dengue
fever, vector control remains the only way to protect human populations.
However, even for vector-borne diseases with effective treatments the high cost of treatment
remains a huge barrier to large amounts of developing world populations. Despite being
treatable, malaria has by far the greatest impact on human health from vectors. In Africa, a child
dies every minute of malaria; this is a reduction of more than 50% since 2000 due to vector
control. In countries where malaria is well established the World Health Organization estimates
countries lose 1.3% annual economic income due to the disease. Both prevention through vector
control and treatment are needed to protect populations.
As the impacts of disease and virus are devastating, the need to control the vectors in which they
carried is prioritized. Vector control in many developing countries can have tremendous impacts
as it increases mortality rates, especially among infants. Because of the high movement of the
population, disease spread is also a greater issue in these areas.
As many vector control methods are effective against multiple diseases, they can be integrated
together to combat multiple diseases at once. The World Health Organization therefore
recommends "Integrated Vector Management" as the process for developing and implementing
strategies for vector control.
Investigate or Know the Following before Deciding on Control Intervention:
- Breeding sites
- Resting sites
- Transmission
- Blood source
- Dispersal range
- Population dynamics
Methods of Vector Control
Vector control focuses on utilizing preventive methods to control or eliminate vector
populations. Common preventive measures are:
Habitat and environmental control
Removing or reducing areas where vectors can easily breed can help limit their growth. For
example, stagnant water removal, destruction of old tires and cans which serve as mosquito
breeding environments, and good management of used water can reduce areas of excessive
vector incidence.
Further examples of environmental control is by reducing the prevalence of open defecation or
improving the designs and maintenance of pit latrines. This can reduce the incidence of flies
acting as vectors to spread diseases via their contact with feces of infected people.
Reducing contact
Limiting exposure to insects or animals that are known disease vectors can reduce infection risks
significantly. For example, bed nets, window screens on homes, or protective clothing can help
reduce the likelihood of contact with vectors. To be effective this requires education and
promotion of methods among the population to raise the awareness of vector threats.
Chemical control
Insecticides, larvicides, rodenticides, lethal ovitraps and repellents can be used to control vectors.
For example, larvicides can be used in mosquito breeding zones; insecticides can be applied to
house walls or bed nets, and use of personal repellents can reduce incidence of insect bites and
thus infection. The use of pesticides for vector control is promoted by the World Health
Organization (WHO) and has proven to be highly effective.
Biological control
The use of natural vector predators, such as bacterial toxins or botanical compounds, can help
control vector populations. Using fish that eat mosquito larvae, the use of cat fish to eat up
mosquito larvae in pond can eradicate the mosquito population, or reducing breeding rates
by introducing sterilized male tsetse flies have been shown to control vector populations and
reduce infection risks.
Disposal of Carcasses
When animals die or are slaughtered on farms, carcasses and parts that are unfit for use as food
should be disposed of properly. Safe and environmentally responsible disposal of animal
carcasses, whether an individual death or during significant mortality events, is an essential
consideration.
Information on the safe and lawful disposal of carcasses can be obtained from local
environmental protection agencies. When the circumstances under which death has occurred
suggest a transmissible disease or toxic hazard, the nearest animal health official should be
notified immediately.
As general precautions, persons handling carcasses and disinfectants should wear protective
clothing and be properly equipped to complete the tasks of disposition and disinfection.
Premises should be promptly cleaned in a manner that prevents any infectious or toxic health
hazard to domestic or wild animals or people.
The method of disposal should preclude contamination of soil, air, and water. Hides and other
parts of animals that have succumbed to infectious diseases or toxins should be safely disposed
of and not retained for use.
RENDERING OF CARCASSES:
Rendering is the process of converting animal carcasses to pathogen-free, useful byproducts
such as feed protein. In the process of rendering, the carcasses are exposed to high temperatures
(about 130 C or 265 F) using pressurized steam to ensure destruction of most pathogens.
Ordinarily, rendering is a safe, rapid, and economic method of disposal of carcasses. Renderers
are required to use equipment and methods that prevent health hazards. Local regulations
specify requirements for transportation of carcasses to rendering plants. During transportation,
biosecurity must be considered to avoid spreading infectious agents into the environment.
BURIAL OF CARCASSES:
When a site acceptable to the local environmental protection agency is available, burial is
usually the preferred method of disposal. In selecting a burial site, it is necessary to consider
the adequacy of soil depth and to avoid underground electrical cables, water pipes, gas pipes,
septic tanks, and water wells. The prevention of secondary toxicosis or exposure to infectious
agents must be considered (eg, the burial of a carcass infected with blastomycosis could
potentially contaminate the soil and groundwater, putting scavengers at risk).
The burial pit or trench should be at least 2.3 m wide and 3 m deep (7 × 9 ft). The pit is a cavein hazard and must not be entered without proper shoring, and any other appropriate
precautions should be taken. At this depth, 1.3 m2
(15 ft2
) of floor space will accommodate a
mature bovine or equine carcass, 5 mature pigs or sheep, 100 mature chickens, or 40 mature
turkeys. For each additional meter (3 ft) in depth, the number of animals per 1.3 m2
of floor
space may be doubled. Contaminated litter, soil, manure, feed, milk, or other material should
be placed in the pit with the carcasses and covered with at least 2 m (6 ft) of soil. The covering
soil should not be compacted. Decomposition and gas formation cause cracking, bubbling, and
leaking of fluids from a compacted burial site. The soil should be mounded and neatly graded.
Certain landfills are licensed to accept animal carcasses. Check with the landfill in your area. If
this is allowed, all biosecurity practices should be followed during transportation.
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| Disposal of Carcasses - Burial, Burning and Composting Methods |
BURNING OF CARCASSES:
Burning in an incinerator that is operated in compliance with local laws and ordinances is an
excellent means to dispose of one or a few carcasses and is the preferred means for sheep with
scrapie and cattle with BSE.
Burning carcasses in an open site should be done only when legally permitted. Burning poultry
carcasses should be considered only when burial is not feasible. The burn site should be away
from public view and on flat, open ground that is clear of buildings, hay or straw stacks,
overhead cables, and shallow underground pipes or cables. Locations upwind from houses,
farm buildings, roads, or populated areas, and those from which precipitation runoff may
contaminate the environment, should be avoided.
Carcasses must be placed on a quantity of combustible supporting materials sufficient to
reduce them completely to ashes. The material must also be arranged in a manner to permit an
adequate flow of air to the fire. Gasoline or other highly volatile combustible liquids should
not be used.
To prepare the fire bed, an area of ground should be staked out to accommodate the number of
carcasses to be burned: 8 × 3 ft for each mature cow or horse, 5 mature pigs or sheep, 100
mature chickens, or 40 mature turkeys. The fire bed burns best if at a right angle to the
prevailing wind.
Under favorable conditions, burning should be complete in 48 hours. Additional combustible
material should be added as needed. When the fire has died out, the ashes should be buried and
the area cleaned, graded or plowed, and prepared for seeding.
COMPOSTING CARCASSES:
Developed for use on poultry farms, composting has been successfully used for swine, cattle,
horse, sheep, and goat carcasses. The proper balance of material (oxygen, moisture, nitrogen,
and carbon) is required for this natural degradation process to reach a temperature of 130°-
150°F, which is sufficient to kill most disease-causing organisms, allowing the end product to
be suitable for use as a soil amendment. However, toxins and any medications or drugs in the
animal at the time of death will not necessarily be degraded through this process. Care should
be taken to protect the compost from excessive rain and to secure it from predators.
OTHER DISPOSAL METHODS FOR CARCASS:
Tissue digestion, fermentation, and dry extrusion methods have been developed to process
certain dead animals and animal waste, destroy pathogenic organisms, reduce volume, and
produce feedstuffs. Tissue digestion, both alkaline and thermal degradation, may be available
in animal diagnostic laboratories. Local environmental protection agencies and state
agriculture departments should be consulted concerning the acceptability of these and other
possible alternative disposal methods.
DISINFECTION OF PREMISES AFTER CARCASS DISPOSAL:
Removal and safe disposal of manure, feed, and debris by burial or burning, followed by
thorough scraping and cleaning of all buildings and equipment, must precede the application of
chemical disinfectant. Except for steam cleaning, cleaning with aqueous solutions is practical
only at temperatures above freezing. A cleaning agent such as trisodium phosphate or sodium
carbonate dissolved in hot water will facilitate cleaning. All traces of the cleaning agent must
be rinsed away with clear water before disinfectant is applied because some may inactivate the
disinfectant. Provision must be made to contain and safely dispose of cleaning solutions, rinse
water, and disinfectant.
Disinfectants recommended for general use on surfaces free of organic matter are sodium or
calcium hypochlorite (1,200 ppm available chlorine), iodine, phenol, and quaternary
ammonium compounds. Newer disinfectants use a combination of products (eg, quaternary
ammonia and glutaraldehyde) to enhance efficacy.
Stray and Fallen Animal Management
Stray animals roam about freely and create nuisance for the community in a number of ways
including damage to crops. They can be a serious hazard for vehicular traffic especially in
congested urban areas. These animals are more likely to be exposed to diseases and
environmental toxicities. When old and weak, their movements become restricted. Thus, the
dung and urine excreted by these animals become serious threats to environmental safety.
Besides, the filth created by such animals helps in the propagation of a variety of insects. Fly
breeding can become a real threat to community health and environment.
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| Stray and Fallen Animals in India, mainly Street Dogs. |
The menace of stray animals can be minimized by collecting these animals in what are called
cattle pounds which are managed by pound keepers. The activity is regulated by the cattle
trespass act, 1921.
There are a number of private organizations that deal with the problem of old and decrepit
animals. In recent times, however, some goshalas have begun keeping even healthy for breeding
purpose and production. The goshalas are supported by charitable organization and occasional
grants from the Government sources.
There has been a growing awareness about the welfare of animals. The activities concerning
animal welfare in India are regulated by Animal Welfare Board of India through the provision of
Prevention of Cruelty to Animals act, 1960.
Stray animals dying in open areas cause enormous damage to environment. They not only
pollute the environment with foul gases/ odours but also invite vultures and other birds and wild
animals to create nuisance. These animals need to be collected immediately and disposed off in
an economic and efficient manner by cremation, burial, rendering or by composting as relevantly
suitable.
Previous VPE notes of Environmental Hygiene are Environment & Ecosystem, Biodiversity, Natural Resources, Pollution, Water sources, contamination and Evaluation, Water Purification & Sewage Disposal, Disaster Management, Biomedical Waste Management, Farm waste Management, Global Warming etc. Hope the note will benefited you. You can contact us by using Contact form for pdf file of this note. For any query knock us. Stay tuned. Thank You. Happy Learning!
