Vector and Reservoir Control | Stray and fallen animal management and Carcass Disposal.

(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.

Stray and fallen animal management and Carcass Disposal.

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: 
  1. Human reservoir 
  2. Animal reservoir, and 
  3. 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.

Disease Reservoir

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.

Vector Control

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 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. 


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. 

Disposal of Carcasses -  Burial, Burning and Composting Methods
Disposal of Carcasses -
Burial, Burning and Composting Methods


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. 


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. 


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. 


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.

Free Animals, Street Dogs
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 & EcosystemBiodiversityNatural ResourcesPollutionWater sources, contamination and EvaluationWater Purification & Sewage DisposalDisaster ManagementBiomedical Waste ManagementFarm 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!
Veterinary Public Health