tuberculosis

Tuberculosis

Imtiaz Ahmad

2009-VA-535

Student of Ph.D

(Medicine)

Implications

 Bovine tuberculosis is a human health

issue in many countries where the milk

is not pasteurized and there are high

rates of human infection

 Bovine TB in Pakistan is an economic

issue!!

What is Tuberculosis?

 Tuberculosis (TB) is a infectious disease

of both animals and humans

 It is caused by Mycobacterium

Mycobacterium

 Unique bacteria

 Cell walls contain a lot of waxy material (mycolic

acid)

– inhibits the uptake of nutrients into the bacterial cell

– causes the cell to clump

 these factors contribute to the slow growth rate

 Mycobacterium do not grow outside of a host

except in cultured media

– Slow growth rate

– Multiply approximately once every 20 hours

Cont…..



 Require oxygen for growth

 Very heat sensitive

 Can be killed by a weak solution of

common household bleach

– (1 part bleach to 9 parts water)

 Can remain viable for extended periods of

time in cold weather

Three Types of Tuberculosis



 Mycobacterium bovis (bovine)



 Mycobacterium avium (bird)



 Mycobacterium tuberculosis

Mycobacterium bovis

 Bovine TB can be

transmitted from

livestock to humans,

deer and other

animals

 No other organism

has as great a host

range as bovine TB

 Bovine TB can infect

all warm-blooded

vertebrates

Mycobacterium avium

 Can affect all species

of bird

 Can affect

cattle

Mycobacterium tuberculosis



 Primarily affects

humans

 Can be transmitted

 to cattle, and dogs

TB Transmission



 Can be transmitted from animals to

humans and vice versa

 Young animals and humans can contract

the disease by drinking raw milk from

infected dams

 Can be transmitted through saliva and

other discharges of infected animals

 Most common means of transmission

– RESPIRATION

Who is at risk?

 Animals kept in close

contact with other

infected animals in

enclosed areas like

barns are at greatest

risk for exposure to

bovine TB.

Animal Immune Response



 Immune system recognizes bacteria

 Inflammatory cells (macrophages) are

sent to dispose of it

 Mycobacterium is resistant to destruction

– once ingested by the macrophages it may

replicate and kill the macrophage

Cont…



 Immune system continues to send

macrophages to help destroy the bacteria

 Results in an accumulation of living and

dead macrophages at the site of the

bacteria

 Accumulation is called a tubercle

 Thick capsule may form around the

tubercle; called a granuloma









Pericardial granuloma

Diagnosing

Bovine TB

Steps in Diagnosis



 The result of each on farm test

determines if follow up tests are

necessary

 Cattle suspected of being infected after

CFT test and CCT test are submitted to an

animal diagnostic laboratory for necropsy

(animal autopsy)

– gross examination

– histological (microscopic) examination

 Upon submission animals are closely

examined for gross lesions suggestive of

bovine TB

 Lymph nodes are closely examined

 Multiple tissue samples are taken for

histopathological examination









Infected Mesenteric lymph node

Gross Lesions

– Characteristic gross lesion of an animal

infected with bovine TB is the presence of

“tubercles” within the body

– A tubercle is a white nodule usually 1mm-2cm

in diameter within a lymph node or organ

– Commonly found in the thoracic cavity

– May be found in the liver or other major

organs

Cont…..



 Finding gross lesions is not conclusive

evidence that the animal is infected with

the disease

 Further testing

is required



Lesions in the lungs of a 2 yr

old heifer

Histopathology



 The tissue samples collected

during the necropsy are

examined for histopathological

(microscopic) lesions

 Most common lesion associated

with bovine TB is the granuloma

Acid Fast Staining



 Unique properties of the cell wall

allow a special stain to be used

 This stain, called acid-fast stain,

allows for bacteria to be

visualized

Process

 Tissue is ground into small pieces

 Treated to destroy non-mycobacteria

 Concentrated by

centrifugations

 Applied to

microscope slide

 Slide is stained so

that mycobacteria can be seen

Culture

 Ifthe animal is suspected of

being infected with bovine TB,

attempts are made to grow

Mycobaterium bovis from tissue

samples collected during

necropsy

Process

 Culturing is performed under specific

conditions that favor growth of the

bacteria

 Culturing usually takes 8 to 16 weeks

Polymerase Chain Reaction (PCR)



 Used to detect the presence of DNA that is

specific to the organism of interest

 PCR amplifies the specific portion of DNA

 This product can be easily visualized using

standard laboratory procedures

 PCR is very sensitive

– Can detect an organism even when present at very low

levels

Cont…



 PCR is used only on tissues that have

histological evidence of bovine TB

 Results are available within seven days

 Positive results suggest that the animal is

infected with TB

 Culturing confirms if the strain is bovine

TB

The Human Disease



 Individuals can be infected without knowing it

 Due to the slow growth rate disease usually

takes months to develop

 Organism may lie dormant within a host’s body

for its lifetime without causing progressive

disease

 Infected humans who have not developed the

active disease can be treated to prevent the

disease from occurring

Initial Infection



 Causative bacteria (this can include

bovine TB) enter the body and settle in a

clump on the host tissue

 Bacteria multiply for several weeks

 Body’s immune system recognizes their

invasion and an immune response begins

Immune Response



 The immune response in humans is called

“cell mediated”

 Cells of the lung begin to multiply to form

a wall around the invading bacteria

 This takes on the shape of a small,

swollen tube

– known as a “tubercle”

Cont….



 At this stage of infection the tubercle is

commonly sealed off and transformed into scar

tissue

 Bacteria become dormant

 No longer affect the body

 Human host can continue to live normally with

one or several dormant tubercles

 As long as the immune system remains strong

the infection may be controlled and usually does

not spread

Weak Immune System



 Bacterial infection will grow and spread

 Tubercles break open, pus will flow out

and infect other regions of the lung and

body with bacilli

 When infection occurs again it begins to

make holes in the lung

 Forms many more tubercles which

develop into “cavities”, or pits in the

lungs

Cont…



 The pus from infected lungs is coughed

up

– often called “sputum”

 Anyone producing sputum from a

tuberculous lung is considered infectious

and may spread the disease to other

people or animals

Active Tuberculosis



 Consumes the lungs

– causes large lesions in the tissue which

prevents the lungs from working properly

 Can eventually lead to death in an

untreated individual

Bovine Tuberculosis Livestock Testing Procedures

Caudal Fold Tuberculin Test (CFT test)



 First screening step in theTB-testing process

Handling Equipment



 Veterinarian will use the on-farm

equipment or set up additional

equipment



 Animals are moved into handling

equipment for testing

Caudal Fold Tuberculin Test



The Purified Protein

Derivative (PPD)

tuberculin is

injected intrader-

mally of the caudal

tail fold, under the

animal’s tail

Cont….



 Some veterinarians will make a mark on

the animal’s hide to indicate which side of

the caudal tail fold was injected



 The animal is also given a unique,

permanent identification number, usually

an ear tag. Registration tattoos may be

used as official identification

cont….



 The injection site is examined 72 hours

later, plus or minus 6 hours



 The same veterinarian who injected the

caudal fold tuberculin must examine the

injection site



 The veterinarian will feel and observe the

injection site

Cont….



 Five to seven percent of the cattle,

goat, population will respond to the

CFT test

– This may happen because the animal

was exposed to another disease that

causes the response, for example

 Mycobacterium avium (Bird TB)

 Mycobacterium Paratuberculosis (Johne’s

Disease)

Cont…



 If there is any response at the injection

site

– swelling

– redness

– hardness

– etc.

 The animal is considered suspect

(responder) and further testing is required

Cont….



 The herd will be quarantined if even

one animal is suspect



 This means no animals can come

into the herd and no animals can

move out of the herd

Comparative Cervical Tuberculin

(CCT) Test



 This test is only done on animals

that respond to the caudal fold test

(CFT)



 The CCT test must be done within 10

days of the injection date of the CFT

Handling Equipment

 Veterinarian will use the on-farm equipment or

set up additional equipment

 Animals are moved into handling equipment for

testing

 Once the animal is secured a section of the neck

is shaved in two places before administering the

CCT test between (intradermally) the skin layers

on the animal’s neck

Skin thickness is

measured using

a special caliper

and then the

veterinarian will

inject avian (bird)

tuberculin and

bovine (cattle)

tuberculin into

two shaved sites

on the neck

The animal

is released

from the

handling

equipment

Injection

sites are

Examined

three days

later

Cont…



 The same veterinarian who

administered the CCT test must

examine the injection sites

approximately 72 hours (plus or

minus six hours) later

Cont…



 When observing the injection sites, the veterinarian looks

for differences in the two sites, and measures the skin

thickness with a special caliper

Cont…



 Swelling is often the reaction to the avian TB

injection.

– Producers should not be alarmed



 The veterinarian or an assistant records the tag

number and test results



 Test results are plotted on a scattergram. Based

on where the results fit on the graph, the animals

will be classified

Classifications



Negative



Suspect



Reactor

Negative

 These animals are considered TB

negative



 If the entire herd tests negative then

the quarantine is released

Suspect

 An animal whose response to the CCT

test is plotted midway on the graph is

classified as a suspect

 Herd owners must decide whether to:

– have the suspect animal removed for

euthanasia

– have the animal re-tested on the farm after 60

days

Re-Test

 If the owner chooses to wait and re-test the

animal:

 The herd remains under quarantine until the

second CCT test results are available

 Animals that respond to two CCT test are

reclassified as reactors and arrangements are

made for removal from the farm

 Classification as a suspect does not mean the

animal has bovine TB

Reactor

 An animal is classified as a reactor if

– its response to the CCT test falls into

the reactor range on the scattergram

– it plots as a suspect on the graph on

two separate CCT tests

 Classification as a reactor does not

mean the animal has bovine TB

Cont…



 The animal is removed from the farm

for necropsy and further laboratory

tests

 The herd remains quarantined until

test results are available.

 If laboratory results show definitive

signs of bovine TB, the animal is

classified as a reactor

Cont…



 Milk from reactor animals cannot be put

into the milk bulk tank or consumed by

humans or animals



 Livestock producers are advised to keep

reactor animals confined and separated

from the rest of the herd until they can be

removed from the farm

Necropsy and Laboratory Testing



 Animals removed from the farm go to the

Animal Health Diagnostic Lab for

necropsy and histopathology



 Scientists look for:

– internal lesions

– swollen lymph nodes

– other signs of disease

Mesenteric lymph node

Cont…



 Tissue samples are collected and

sent to the lab for culturing and

further diagnostic testing



 The herd remains under quarantine

until laboratory test results are

available

Tuberculosis lesions in the lungs of a

two-year-old heifer

cont…

Cont….

Cont….

Cont…

 Thank you