Quick Review in Veterinary Epidemiology

TERMINOLOGY

• Attack rate: A variant of an incident rate, applied to a narrowly defined population observed for a limited period of time, such as during an epidemic.
• Carrier: A person or animal without apparent disease who harbors a specific infectious agent and is capable of transmitting the agent to others.
• Crude mortality rate: The mortality rate from all causes of death for a population.
• Cumulative frequency curve: A plot of the cumulative frequency rather than the actual frequency for each class interval of a variable.
• Cumulative frequency: In a frequency distribution, the number or proportion of cases or events with a particular value or in a particular class interval, plus the total number or proportion of cases or events with smaller values of the variable.
• Death-to-case ratio: The number of deaths attributed to a particular disease during a specified time period divided by the number of new cases of that disease identified during the same time period.
• Endemic/Enzootic: Disease occurring in a particular area.
• Epidemic/Epizootic: Disease that affects many individuals or animals over a wide area.
• Hyper endemic disease: A disease that is constantly present at a high incidence and/or prevalence rate.
• Immunity, active: Resistance developed in response to stimulus by an antigen (infecting agent or vaccine) and usually characterized by the presence of antibody produced by the host.
• Immunity, herd: The resistance of a group to invasion and spread of an infectious agent, based on the resistance to infection of a high proportion of individual members of the group.
• Immunity, passive: Immunity conferred by an antibody produced in another host and acquired naturally by an infant from its mother or artificially by administration of an antibody-containing preparation (antiserum or immune globulin).
• Incidence rate: A measure of the frequency with which an event, such as a new case of illness, occurs in a population over a period of time.
• Incidence: the number of cases of an infection occurring during a given period of time in relation to the population unit in which they occur
• Incubation period: A period of subclinical or in apparent pathologic changes following exposure, ending with the onset of symptoms of infectious disease.
• @ Independent variable: An exposure, risk factor, or other characteristic being observed or measured that is hypothesized to influence an event or manifestation (the dependent variable).
• Latency period: A period of subclinical or in apparent pathologic changes following exposure, ending with the onset of symptoms of chronic disease.
• Morbidity: Any departure, subjective or objective, from a state of physiological or psychological well-being.
• Mortality rate: A measure of the frequency of occurrence of death in a defined population during a specified interval of time.
• Pandemic/Panzootic: Spread over large area of the world, crosses the border.
• Prevalence: The number or proportion of cases or events or conditions in a given population.
• Sporadic: A disease that occurs infrequently and irregularly.
• Veterinary public health: "Veterinary Public Health is the contribution to the complete physical, mental, and social well-being of humans through an understanding and application of veterinary medical science."
• Virulence: relative infectiousness of a parasite
• Zoonosis: An infectious disease that is transmissible under normal conditions from animals to humans and vice versa.

NOTIFIABLE DISEASES OF NEPAL  

• Anthrax•Atropic Rhinitis                •Duck Virus Hepatitis
• Bovine Brucellosis     •Bovine Tuberculosis        •Ovine Foot-rot
• Aujeszky's Disease    •Buffalo Pox                        •Ovine Epididymitis
• Avian Tuberculosis   •Rinderpest                         •Caprine and Bovine Brucellosis
• Sheep and Goat Pox • Classical Swine Fever     •PPR (Peste des pestis ruminants)
• Porcine Brucellosis   •Duck Virus Enteritis       •Contagious Caprine Pleuropneumonia
• Chicken Anaemia Virus Infection                        •Avian Influenza/Fowl Plague
• Contagious Bovine Pleuropneumonia

 Note: FMD and Newcastle Disease are Notifiable animal diseases, but they are not incorporated in this list as they are endemic in Nepal.

TRANSBOUNDARY ANIMAL DISEASES-Quarantine Days

Transboundary animal diseases are defined as: those that are of significant economic, trade and/or food security importance for a considerable number of countries; which can easily spread to other countries and reach epidemic proportions; and where control/management, including exclusion, requires cooperation between several countries.

FMD- 14 Days,  Fowl plague - 21 Days,   Sheep & Goat pox- 21 days,  Renderpest- 21 days,  PPR- 21 Days, Vesicular stomatitis - 21 Days, ND - 21 days, Lumpy skin disease- 21 Days, Swine vesicular disease - 28 Days,  Rift valley disease - 30 days, Blue tongue - 40 Days, African horse sickness - 40 Days, Classical swine disease - 40 days, CCPP - 6months, Notifiable Avian influenza - (3-5) Days.

ZOONOTIC DISEASES

• Bacterial: Anthrax, T.B., Bricellosis, H.S., B.Q., Salmonella, Endometritis
• Viral: FMD, BVD, Rabies, BT, Pox, Rift valley fever
• Parasitic: Gid, Hydatidosis, Lung worm, Cysticercosis
• Protozoal: Babesiosis, Toxoplasmosis, Theleriosis
• Others: BSE, Scapie, CCPP,CBPP

WHY ZOONOTIC DISEASE SURVEILLANCE?

• Evaluate the health of animal populations at risk. Investigate common source outbreaks and any connections between infected herds/flocks and human cases.
• Estimate the extent and geographical distribution of the disease in the animal population.
• Identify high risk areas and animal populations.
• Evaluate the need for interventions, establishing priorities and allocating resources.
• Facilitate planning and communication in both human and animal health sectors.
• Develop a database for regular communications to people and institutions directly involved in anthrax control and prevention (including the media).
• Evaluate prevention and control activities by monitoring disease trends and measuring the impact of programmes (programme evaluation and cost-effectiveness).
• Monitor changes in the epidemiological patterns of the disease to be able to modify control activities appropriately, by monitoring:
• changes in the animal populations and geographical areas involved; and
• the incidence of anthrax in livestock in order to predict the possible occurrence in humans

MILK BRONE DISEASES

• Infection of milk directly from the cow: Bovine TB, Undulant fever
• Infection from men to cow & then to milk: Theses diseases are essentially of human nature but can become established in cow’s udder. e.g. septic sore throat.
• Direct contamination of milk from human beings: Typhoid fever, Paratyphoid fever, Dysentery
• Indirect contamination of milk from human beings: Typhoid

Sources of contamination of milk & their control

• Interior to the udder - Check for mastitis, Discard fore milk
• Exterior to the udder - Wash and wipe udder, Clip the udder and flanks, Dry milking, Use small top milking pot
• Barn air & dust - Keep milk closed
• Flies and others insects - Eliminate breeding places, Fly control with fly springs, fly traps etc.
• The milkers  - Clean habit, Dry milking
• Utensils - Clean, sterilized and dry before use 

RISK ANALYSIS

Risk analysis is the process of defining and analyzing the dangers to individuals, businesses and government agencies posed by potential natural and human-caused adverse events.

The OIE provides the following recommendations for risk analysis:

• risk analysis should be objective and defensible;
• the process should be transparent and consistent;
• risk management and assessment functions should be separated to ensure independence of decision-making process and evaluation of the risk;
• risk management should be conducted using a policy framework;
• risk assessment should be based on sound science;
• communication between managers, assessors and stakeholders is essential; and
• Developing countries should be helped to cultivate and access skills required for the risk assessment effort of harmonization

Major risk factor related to transmission of trichenella infection in Nepal

The major risk factors related to transmission of Trichinella include:

• exposure of pigs to rodents and wildlife;
• extensive or free-range pig rearing;
• consumption of uninspected meat;
• failure of meat inspection procedures;
• consumption of meat from backyard pigs;
• consumption of raw infected horse meat;
• consumption of uninspected pig meat sausage-like products;
• consumption of meat from wild game (especially wild boars and bears);
• inadequate cooking of pig meat; and
• lack of adequate diagnostic procedures

COST analysis of the disease control program: When farmers must make economic decisions, three competing goals must be considered:

• maximization of profit,
• avoidance of risk, and
• personal satisfaction

If a decision has a relatively long time-frame, then the time value of costs and of benefits also must be considered. There are a variety of ways to structure the comparison between disease control programs. If disease is endemic, a partial budget analysis is recommended. If, instead, probabilities must be included in the calculations, then the recommendation is to use pay-off table analysis or to draw a decision tree (the latter especially if there are sequences of decisions).

THE HACCP Concept

Hazard Analysis Critical Control Points (HACCP) is an international food safety system that deals with the control of factors affecting the ingredients, product and processing of food. It is widely recognized by scientific authorities and international organizations as the most effective approach available for producing safe food. The goal of HACCP is to identify biological, chemical and physical hazards and to include preventive measures throughout the process which would stop these hazards before they begin. These measures would, in turn, prevent unsafe food from reaching the consumer. In the United States, meat and poultry are inspected are regulated under HACCP by the United States Department of Agriculture (USDA) Food Safety Inspection Service (FSIS). HACCP regulations ultimately make industry responsible for food safety.

The introduction of specific HACCP concept involves the following:

• identifying hygienic hazards
• ranking these hazards
• defining the critical limit
• identifying the critical control points
• recommending necessary control
• record keeping
• verification procedures to ensure efficiency
• tests to ensure that the concept is working

The Hazard Analysis Critical Control Point (HACCP) Concept was introduced in the food industry in 1971 to ensure that there would be effective control of the quality of processed foods. The World Health Organization (WHO) recommends that this concept also be applied to Meat Inspection and Meat Hygiene in particular to control salmonellosis. It can also be used to reduce bacterial contamination during slaughtering and dressing and to ensure quality control in Meat Inspection.

MEAT INSPECTION –ANTE-MORTEM, POSTMORTEM AND RE-INPECCTION

The objectives of meat inspection programme are two fold:

1. To ensure that only apparently healthy, physiologically normal animals are slaughtered for human consumption and that abnormal animals are separated and dealt with accordingly.
2. To ensure that meat from animals is free from disease, wholesome and of no risk to human health.

ANTEMORTEM INSPECTION

Some of the major objectives of antemortem inspection are as follows:

• to screen all animals destined to slaughter.
• to ensure that animals are properly rested and that proper clinical information, which will assist in the disease diagnosis and judgement, is obtained.
• to reduce contamination on the killing floor by separating the dirty animals and condemning the diseased animals if required by regulation.
• to ensure that injured animals or those with pain and suffering receive emergency slaughter and that animals are treated humanely.
• to identify reportable animal diseases to prevent killing floor contamination.
• to identify sick animals and those treated with antibiotics, chemotherapeutic agents, insecticides and pesticides.
• to require and ensure the cleaning and disinfection of trucks used to transport livestock.

Some of the abnormalities which are checked on antemortem examination include:

• Abnormalities in respiration
• Abnormalities in behaviour
• Abnormalities in gait
• Abnormalities in posture
• Abnormalities in structure and conformation
• Abnormal discharges or protrusions from body openings
• Abnormal colour
• Abnormal odour

POSTMORTEM INSPECTION

Postmortem inspection should provide necessary information for the scientific evaluation of pathological lesions pertinent to the wholesomeness of meat. Professional and technical knowledge must be fully utilized by:

• Viewing, incision, palpation and olfaction techniques.
• Classifying the lesions into one of two major categories - acute or chronic.
• Establishing whether the condition is localized or generalized, and the extent of systemic changes in other organs or tissues.
• Determine the significance of primary and systemic pathological lesions and their relevance to major organs and systems, particularly the liver, kidneys, heart, spleen and lymphatic system.
• Coordinating all the components of antemortem and postmortem findings to make a final diagnosis.
• Submitting the samples to the laboratory for diagnostic support, if abattoir has holding and refrigeration facilities for carcasses under detention.

BIO-SECURITY FOR DAIRY CATTLE

Animal + Infectious Agent + Environment = Disease

Management Practices on

• Biological Hazards        •Chemical Hazards     •Physical Hazards

The Spread of Disease

• The introduction of diseased cattle or healthy cattle incubating disease.
• Introduction of healthy cattle who have recovered from disease but are now carriers.
• Vehicles, equipment, clothing and shoes of visitors or employees who move between herds.
• Contact with inanimate objects that are contaminated with disease organisms.
• Carcasses of dead cattle that have not been disposed of properly.
• Feeds, especially high risk feeds which could be contaminated
• Impure water (surface drainage water, etc.).
• Manure handling and aerosolized manure and dust
• Animals other than cattle (horses, dogs, cats, wildlife, rodents, birds and insects).

Major Components of Bio-security

Isolation                  Traffic control                Sanitation            vaccination

Biosecurity disinfectants for boot wash

• Phenolic Disinfectants: Lysol, One-stroke Environ, LpH are all excellent disinfectants ½ ounce (15 cc) per gallon of water.
• Iodophors: Betadine, Tamed Iodine and others  0.5 to 1% iodine solutions 2-4 (60-120 cc) ounces per gallon of water
• Hypochlorites: Clorox or other brands of bleach 5.25% Na hypochloride  2-4 ounces (60-120 cc) per gallon of water for boot wash
• Chlorhexidine: Nolvasan, other chlorhexidine gluconate (0.5%)