Investigating Disease Outbreaks | Animal Husbandry & Veterinary Science Optional for UPSC PDF Download

Investigating Disease Outbreaks

Investigating a disease outbreak for diagnosis and identification of the causative agents require a comprehensive, scientific, and open-minded approach. The process involves:

History of the Outbreak

• Recording the date of the initial and subsequent occurrences of the disease.
• Documenting the types and ages of the animals affected.
• Considering the type of cultivation and season prevalent in the area during the outbreak.
• Examining previous outbreaks in the same or adjacent areas.

History of the Illness

• Counting the number of animals in the area, those exposed to the disease, those showing clinical symptoms, those who died, and those who recovered.
• Recording the period of illness and the incubation period.
• Noting the treatment given and the recovery observed.

Other Determinants of the Outbreak

• Assessing the speed of the outbreak's spread.
• Identifying vectors and their role in disease transmission.
• Evaluating the management practices adopted in the location.
• Investigating the source of feed, water, and transportation.
• Examining the access of visitors to the animals in the farm and other organized animal houses.
• Checking the status of the animals (whether in production, rest, breeding seasons, in gestation, etc.)
• Tracking the movement of the animals, including new introductions to the farm.

Collecting Materials for Investigation

Before proceeding with the investigation, the investigator must have all necessary materials for specimen collection. The collected specimens can include secretions, excretions, tissues, and body fluids like blood, serum, lymph, etc. from the animals.

For Bacteriological Examinations:

• Collect samples with aseptic precautions to avoid contamination.
• Immediately store in a refrigerator at 4.5°C.
• If preservation for 8-10 hours is required, replace ice during transport.
• Transport over ice: use a watertight container and pack in ice; for boat transport, dry ice in a thermocole box is suitable.

Materials for Bacterial Diseases:

• Heart blood swab
• Smear from tissue lesions, blood, body secretions, and excretions
• Collection of pus materials
• Intestinal contents
• Urine samples
• Milk samples
• Skin lesions and smears from pustules and vesicles

Viral Diseases:

• Refrigerate samples until prepared and inoculated into tissue cultures.
• Inoculate on the collection day or within 24 hours if possible.
• If delay expected, store specimens at -20°C; -70°C is more suitable for virus preservation.
• Use tightly sealed ampoules when storing at -70°C with dry ice to prevent CO₂ effects on virus viability.
• Virus transport medium can be used for mailing swabs. Place the swab directly into the transport medium, closing the screw cap tightly after adding 1.2 ml of PBS with antibiotics.

Parasitic Diseases:

• Faecal samples/Dung samples
• Blood smear and wet film
• Lymph node biopsy smear
• Scrapings
• Intestinal mucosae
• Nasal washings, nasal discharge smear, and washings smear
• Collection of ectoparasites and other vectors
• Tissues for histopathological examinations

Fungal Diseases:

• Collect skin scrapings, hair follicles, and scales.
• Wrap in polythene paper and send for examination.

Reasons for Specimen Spoilage:

• Spoilage of blood and sera can occur due to wet needles, syringes, undue heat or cold, forceful discharge into tubes, bacterial decomposition, and chemical contaminants.
• Spoilage of tissues for bacteriological/virological work may result from contaminated containers, infection during sample collection, improper preservation, lack of refrigeration or cold chain, leakage of preservatives, and breakage of containers during packing or transportation.

General Guidelines for Collecting Materials

• Collect specimens from living or recently dead animals, and as early as possible following the onset of clinical illness.
• Obtain samples from the edges of lesions and include some macroscopically normal tissue.
• Collect samples as aseptically as possible to avoid contamination.
• Always collect specimens before the administration of any form of treatment.
• Submit samples individually in separate watertight containers.
• If transportation to the laboratory is delayed, refrigerate most samples at 4°C and do not freeze.

Interpreting the Diagnostic Results

Several factors need to be considered when interpreting reports from a diagnostic laboratory:

• A negative report doesn't necessarily mean that the suspected microorganism isn't the cause of the disease.
• Many bacteria are ubiquitous, and their isolation may represent contamination of the sample.
• Healthy animals can be subclinical carriers of microorganisms.
• In case of some endemic diseases, two serum samples collected 2-3 weeks apart are required for serology.

Establishment of Animal Health Centres

Animal Health Centres, serving as hubs for livestock health care, play a pivotal role in maintaining and improving livestock health. They provide both preventive and curative aspects of animal health care, including periodical vaccination, treatment of sick animals, performing surgeries, attending to disease outbreaks, castration of scrub bulls, and advising farmers on animal husbandry practices.

Establishment of Disease-Free Zones

Establishing disease-free zones involves a series of broad-based control measures, including:

• Periodical screening of animals for health status.
• Maintaining healthy animals after periodical testing and slaughter.
• Recording and managing disease outbreaks effectively.
• Studying and monitoring weather and seasons.
• Identifying and assessing vector density and vector-free population.
• Periodical vaccinations for various livestock diseases.
• Adopting effective control measures such as Frankel method of vaccination, ring vaccination, border vaccination, belt vaccination, spelling out policies, and elimination of disease reservoirs and carriers in the population.