Vet Medicine Chapter 6: Contact Infections

Chapter Six: Contact Infections

Characteristic Features

• Contact diseases are transmitted through direct or indirect contact from an infected to a susceptible organism
• Infection can occur through:
  • Aerosol (via air droplet)
  • Animate objects (humans and animals carrying the pathogen on their bodies)
  • Inanimate objects (farm equipment, machineries)
• The pathogen's resistance to environmental influences affects the transmission of contact diseases
• Animals that recover from contact diseases often confer sterile immunity
• Relatively efficient vaccines are available for most contact diseases
• Contact diseases were commonly found in temperate climate countries but are now widespread in tropical regions due to various factors

Contagious Bovine Pleuropneumonia (CBPP)

• Caused by Mycoplasma mycoides subsp. mycoides Small Colony- bovine biotype (MmmSC)
• Affects cattle, both Bos taurus and Bos indicus, as well as Asian buffalo, bison, and yak
• Transmission occurs through:
  • Inhalation of droplets from infected coughing animals
  • Close contact with infected animals, especially in the acute phase of the disease
  • Fomites (indirect transmission)
• Morbidity and mortality rates vary, but can be high, with European breeds more susceptible than indigenous African breeds
• The disease is endemic in most African countries and some Asian countries, but has been eradicated from the United States, Australia, Europe, and South Africa

Contagious Caprine Pleuropneumonia (CCPP)

• Caused by Mycoplasma capricolum subspecies capripneumoniae (Mccp)
• Affects goats, with morbidity and mortality rates of 100% and 60-100%, respectively
• Transmission occurs through inhalation, with the organism not surviving for long outside the animal body
• Vaccination with an inactivated mycoplasma F38 vaccine is effective in reducing morbidity and mortality rates

Tuberculosis

• Caused by Mycobacterium bovis
• Affects cattle, as well as other domesticated and wild mammals, including humans
• Transmission occurs through:
  • Inhalation of aerosols
  • Ingestion
  • Breaks in the skin
• The disease is endemic in Africa, parts of Asia, and some Middle Eastern countries, with economic losses including livestock deaths, sterility, and reduced beef and milk production
• Control and prevention methods include test-and-slaughter or test-and-segregation techniques, as well as sanitation and disinfection

Brucellosis

• Caused by various bacteria of the family Brucella
• Affects cattle, swine, sheep, goats, camels, equines, and dogs, as well as humans
• Characteristics of the disease include abortions or reproductive failure in animals and undulating or Malta fever in humans
• The disease is economically important in developing countries that have not had a national brucellosis eradication program### Brucellosis
• Brucellosis is a zoonotic disease that affects cattle, buffaloes, and other animals, caused by the bacterium Brucella abortus.
• It is an economically important cause of abortions in cattle worldwide, except in Japan, Canada, some European countries, Australia, New Zealand, and Israel, where it has been eradicated.
• The disease is found worldwide in cattle-raising regions, including Ethiopia, where it is a significant problem in intensive livestock management.
• The prevalence of bovine brucellosis in intensive livestock management in Ethiopia ranges from 8.11 to 22%.
• B. abortus infections can occur in domestic buffalo, African buffalo, North American buffalo, cervidae, and camelidae, as well as horses and dogs.
• Sexually mature, pregnant cattle are more susceptible to infection than sexually immature cattle of either sex.

Epidemiology

• In animals, B. abortus is usually transmitted by contact with the placenta, fetus, fetal fluids, and vaginal discharges from infected animals.
• The disease can be transmitted through ingestion and mucous membranes.
• Infection usually occurs by ingestion, and animals may become chronic carriers.
• The mammary gland can be infected by direct contact, leading to shedding of the organisms in milk.

Morbidity and Mortality

• In previously unexposed and unvaccinated cattle, B. abortus spreads rapidly, and abortion storms are common, with an abortion rate varying from 30% to 80%.
• In herds where the organism has become endemic, only sporadic symptoms occur, and cows may abort their first pregnancies.

Zoonotic Importance

• Brucellosis is an important zoonosis causing undulant fever in humans, mainly through the ingestion of unpasteurized dairy products.

Control and Prevention

• B. abortus can be eradicated from a herd by test-and-removal procedures or by depopulation.
• Eradication can be accomplished by quarantine of infected herds, vaccination, test-and-slaughter techniques, various forms of surveillance, and tracebacks.
• Infections in other species are generally prevented by controlling B. abortus in its maintenance hosts.

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Hemorrhagic Septicemia

• Hemorrhagic septicemia (HS) is a major disease of cattle and buffaloes characterized by acute, highly fatal septicemia with high morbidity and mortality.
• The disease is caused by certain serotypes of Pasteurella multocida, a Gram-negative coccobacillus residing in the upper respiratory tract of animals.

Epidemiology

• HS is an important disease of cattle and water buffalo in Asia, Africa, and the Middle East.
• The highest incidence is in Southeast Asia.
• Cattle and water buffalo are the principal hosts of HS, with buffaloes being more susceptible.

Transmission

• P. multocida is transmitted by ingestion or inhalation, either during direct contact or via fomites such as contaminated feed and water.

Morbidity and Mortality

• The morbidity rate depends on environmental conditions, herd management, the animals' immunity, and other factors.
• All ages are affected where HS is not endemic, and the morbidity rate can be high.
• In endemic regions, outbreaks often occur when healthy carriers are introduced into a herd.

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Foot-and-Mouth Disease

• Foot-and-mouth disease (FMD) is a highly contagious viral disease that primarily affects cloven-hooved livestock and wildlife.

Epidemiology

• FMD is endemic in parts of Asia, Africa, and the Middle East, and South America.
• In parts of Africa, virus persistence in wild African buffalo makes eradication unfeasible.
• North America, New Zealand, Australia, Greenland, Iceland, and most of Europe are free of FMD.

Host Range

• Cattle, pigs, sheep, goats, and buffalo are susceptible to FMD.
• Many species of cloven-hoofed wildlife may become infected, but they do not play a significant role in the epidemiology of FMD.

Transmission

• Transmission can occur by direct or indirect contact with infected animals and contaminated fomites.
• Routes of spread include inhalation of aerosolized virus, ingestion of contaminated feed, and entry of the virus through skin abrasions or mucous membranes.

Morbidity and Mortality

• In susceptible animal populations, morbidity can reach 100%, but mortality is generally less than 1% in adult livestock.
• Mortality can be higher in young animals and with highly virulent strains of the virus.

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Peste des Petits Ruminants

• Peste des petits ruminants (PPR) is a highly contagious viral disease of small ruminants characterized by fever, ocular and nasal discharges, stomatitis, diarrhea, and pneumonia.

Epidemiology

• PPR occurs south of the Sahara desert and north of the equator in Africa, in most of the Middle East, and in parts of Asia, including much of the Indian subcontinent.
• The four virus lineages are found in different geographic regions.

Host Range

• Among domesticated animals, PPR is primarily a disease of goats and sheep.
• Cattle and pigs are susceptible to infection with PPRV, but they do not exhibit clinical signs and do not play a role in the epizootiology of PPR.

Transmission

• Transmission of PPRV mainly occurs during close contact, inhalation, and through nasal and ocular secretions, saliva, urine, and feces.

Morbidity and Mortality

• The morbidity and mortality rates can reach 100%, particularly in naïve herds.
• During a countrywide outbreak among camels in Ethiopia, the morbidity rate was greater than 90%, and the mortality rate ranged from 5% to 70%.

Control and Prevention

• PPR can be eradicated with a combination of quarantines, movement controls, euthanasia of infected and exposed animals, and cleaning and disinfection of infected premises.
• PPR is controlled in endemic areas by vaccination.
• Animals that recover develop good immunity, which persists for at least four years and possibly lifelong.