Biology Reference
In-Depth Information
ingestion of contaminated food, often unpasteurized milk, and products
made from unpasteurized milk. Human-to-human transmission mostly
occurs through aerosol droplets that are expelled into the air by coughing,
sneezing, laughing, or talking. According to the World Health Organization
(WHO), an untreated person with an active TB infection will infect an aver-
age of 10 to 15 people. Cases can be treated with approved antimicrobials.
However, the course of treatment can take 6 to 12 months, and the emer-
gence of extensively drug-resistant TB (XDR-TB) threatens the ability to treat
the infection. The global mortality rate for TB is 1,577 per 100,000 persons.
It is the most common bacterial cause of human death in the world (Colville
and Berryhill 2007).
TB can cause asymptomatic infections in humans and animals if their
immune systems are able to suppress bacterial replication. This is referred to
as latent TB because the host remains colonized and symptoms can occur later
if the immune system is no longer able to prevent replication. Approximately,
5% to 10% of people with latent TB will develop an active infection at some
point in their lives. In people with active TB, symptoms often involve the pul-
monary system and may include a productive cough, fever, bloody sputum,
and chest pain. Some infections in humans are extrapulmonary, involving
the central nervous system, vascular system, or other organs.
In cattle, TB can either be chronic or acute, depending on the host immune
system and the dose of bacteria. Active infections are characterized by low
fever, decreased milk production, weakness, anorexia, and progressive ema-
ciation. There may also be respiratory symptoms and enlarged lymph nodes.
Just as with humans, latently infected animals may become symptomatic if
their immune system fails to control bacterial replication.
TB is a concern for zoological institutions primarily because it can cause
morbidity and mortality in the animals in their collections, many of which
represent endangered or threatened species (Lacasse et al. 2007). Additionally,
the zoonotic nature of the disease presents a risk to zoo employees han-
dling potentially infected animals. There is also concern among zoological
institutions that strict regulatory measures for TB could be imposed. In the
agricultural system, animals testing positive for TB are culled. This is not a
favorable option for zoos. Further, restrictions may be placed on the transfer
of animals across states lines due to concerns of introducing the disease to
the agricultural industry. These apprehensions call for a reliable method of
diagnosing TB in zoo species, which requires more information about the
tests currently being used and their results.
5.2.2 Creation of the System
In 1996, several zoo elephants were diagnosed with active Mycobacterium
tuberculosis infections (Michalak et al. 1998, Mikota et al. 2001). This led the
Tuberculosis Committee of the United States Animal Health Association
(USAHA) to recommend the creation of a working group to address the
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