How Diseases and Parasites are Spread

4-H Veterinary ScienceExtension Veterinary Medicine 

Texas AgriLife Extension ServiceCollege of Veterinary Medicine and Biomedical Science

Texas A&M Systemhttp://aevm.tamu.edu

Objectives

Discuss the spread of infections by direct means

Discuss the spread of infections by direct means

Discuss the spread of infections by indirect means

Describe the methods by which parasites are spread

Discuss sources of disease

Idea Pathogen has left infected host and looking for

susceptible host

Direct vs. Indirect Transmission

Direct transmission Direct or close contact

Indirect transmission Vectors Vehicles Fomites

Routes of Transmission

Aerosol Oral Vehicle Vector

Mechanical Biological

Sources

A. Carrier/reservoir animals1. Aerosol droplets 8. Milk

2. Nasal fluid 9. Fetal fluid

3. Ocular fluid 10. In utero

4. Saliva 11. Genital fluid

5. Skin 12. Blood

6. Manure 13. Carcass

7. Urine

Vectors (live)

Ticks Flies Mosquitoes Scavengers People

Vehicles (not alive)

Instruments Needles Ear tagger Tattooer Dehorner Nose tong Knife

Utensils Buckets Troughs Boots Clothing

Environment

Soil Water Food Air

Routes of Entry

Susceptible Animals Mouth Vagina Nose Prepuce Eyes Transplacental Skin Venereal Teats Blood

Incubation Period

Long/short

Exposure to symptoms

Exposure to positive tests

During incubation period No symptoms

Negative tests

After incubation period

Symptoms Positive tests

Latent Infections(Recrudescent Infections) Extended incubation period

No symptoms Negative tests

After recrudescence Symptoms Positive tests

Injury Blackleg Malignant edema Black disease Black-neck disease

Diet change/overload Enterotoxemia

Flukes Redwater

Stress IBR/PI3/BVD/BRSV Pasteurella/haemophilus

Pregnancy in heifers Brucellosis

Non-Latent Infections

Normal incubation period

Stress Factors

Nutrition Weather Pregnancy Calving Working Weaning Shipping Breeding Walking

High Risk Herds

Identify sources Separate carrier/reservoir animals

(shedders) Reduce commingling

Vaccinate Susceptible Animals

Not 100% protection No response Improper procedures Mishandled vaccine Expired vaccine Stored opened vaccines Poor quality vaccine Primary dose only

Long/short protection Vaccinate before exposure Does not prevent recrudescence in latent infections

Biosecurity Measures

Raise replacements Purchase animals from clean herds Test purchased animals Vaccinate purchased animals Isolate purchased animals Restrict visitors and vehicle entries Construct buffer zone fencing