Giardia - PowerPoint Presentation

Slide1

GiardiaSlide2

Hazard Identification

What is

Giardia

?

Giardia

is a

single-celled flagellate protozoan

parasite belonging to the

order

Diplomonadida

.

The cells

are unusual in having

two nuclei

.

The

species important

in human illness is

Giardia

intestinalis

(previously referred to as G.

lamblia

, or G.

duodenalis

). Slide3
Slide4

G.

intestinalis

is also

found in a number of animals

, including cattle, cats and dogs.

G.

intestinalis

is

an obligate parasite

and requires a host in order to multiply.Slide5

It is a cause of

gastrointestinal infection

(

giardiasis

) in humans and some other animals, and is found worldwide.

G.

intestinalis

has a

two-stage life cycle

, and

exists in two forms

.

1)

Trophozoite

:

Pear-shaped flagellated

multiplies within the gastrointestinal tract of the host.

excreted in the host’s

faeces

but die quickly.

Is

not

transmissible stage in the cycle

2) Cyst

:

Spore-like resistant cysts within the small intestine.

excreted in the host’s

faeces

.

transmissible stage in the cycle Slide6
Slide7
Slide8

Occurrence in Foods

G.

intestinalis

is

mainly

associated with

surface water

that has been

polluted by human or animal

faeces

But cysts have also been found in a number of

unprocessed foods

, including:

Root crops

Lettuce

Strawberries

G.

intestinalis

:

does not

grow

in foods or in water

does not

multiply

in the environment outside of a suitable hostSlide9

Cysts are

destroyed by heat

and G.

intestinalis

is not normally associated with cooked and processed foods.

Any food that may come into contact with

contaminated water during production

, and where there is no subsequent process that will destroy cysts, may be at risk from G.

intestinalis

contamination.

However,

food

is not

a major vehicle

for the transmission of the parasite.

The

waterborne

and

person-to-person

transmission routes are thought to be much more common that

foodborn

rout.Slide10

Hazard

Characterisation

Effects on Health

G.

intestinalis

can cause an acute

gastrointestinal infection

in humans.

Children

are especially

vulnerable

to infection.

The

mechanism

by which it causes disease is

unclear

.

The

trophozoites

probably

attach to the epithelial cells lining the gut

, but

do not

invade

the cells.

They

may produce a toxin

in the small intestine, but this has not been confirmed.

The

incubation time

for the infection is usually between

1–3 weeks

from ingestion of cysts. Slide11

The main symptom are:

Diarrhoea

Abdominal pain.

Fever

In healthy adults,

symptoms

typically

last

for

1–2 weeks.

The infection is generally

self-limiting

in

most case

s, but

drug treatment is sometimes required.

However, in

immunocompromised

individuals

, infection can be more serious and long lasting, requiring hospital treatment, and occasional

deaths

have been recorded.

The

infective dose

is thought to be

very low

and ingestion of as few as

10 cysts

. Slide12

Incidence and Outbreaks

G.

intestinalis

is probably the

most commonly

reported intestinal parasite in the

developed world

.

The

European countries with the highest reported incidence:

Estonia (24.28 cases per 100 000 people)

Iceland (14.65 cases per 100 000 people)

The results also show that c

hildren aged 0–4 years were most commonly infected.

There are seasonal

peaks of infection

in

spring

and

autumn

.

There were 20075 reported cases of

giardiasis

in the USA in 2005.Slide13
Slide14
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Slide16

Sources

G.

intestinalis

is an

obligate parasite

and thus

originates from the host.

The primary source

of G.

intestinalis

is the

faeces

of infected humans and animals

, which may contain up to

10

9

cysts in a single day.

The cysts are extremely infectious and may be transferred to food via an infected

food handler

, or

through polluted water used for crop irrigation or processing

.

G.

intestinalis

cysts are larger

than those of Cryptosporidium (

9–12

µ

m

diameter) and are

relatively easy to remove

from water using modern

water treatment

methods.

They are also

less

resistant to chlorine

, but

are

not inactivated by the concentrations normally

used to treat water.Slide17

They are much

less

likely to pass through water-treatment

plants into the public water supply system.Slide18

Stability in Foods

G.

intestinalis

cysts

are generally resistant to environmental factors.

Cysts can

persist for months

in

cool

and

moist

conditions.

However, there is little information on their survival and inactivation in foods.

The cysts are

relatively

resistant

to some

sanitisers

and disinfectants

, notably

chlorine

and

ozone

.

G.

intestinalis

cysts

are not heat resistant

and are

destroyed

by conventional

milk

pasteurisation

.

A temperature of

60–70

0

C for 10 min

is reported to

inactivate

cysts completely. Slide19

Therefore, most controlled

cooking processes

used in food production should

destroy

any viable cysts in the product.

Oocysts

can

survive

for significant periods at temperatures

below 0

0

C

, especially in water

But

frozen

storage is reported to cause

inactivation

.Slide20

Control Options

Control measures

for G.

intestinalis

in food processing

focus

largely on the

control of contamination in water

and the management of infected

food handlers

.

Processing

Care should be taken to ensure that

raw-food ingredients

and products that

do not undergo further processing

do not come into contact with contaminated surface water.

Fresh produce should be obtained from suppliers practicing good agricultural practice.

Fresh produce

and other raw foods should only be washed/processed

using potable quality water

.Slide21

Heat processing is an effective

control against G.

intestinalis

cysts in food.

Normal milk-

pasteurisation

processes are effective

, as are recommended ‘‘

Listeria

cook’’ processes for meat products (70

0

C for at least 2 min).

Reheating cooked foods

to at least

74

0

C

will

destroy

cysts immediately.

Freezing

foods for at least

7 days

is also an

effective

control.Slide22

Hygiene

Infected

food handlers

are also a major G.

intestinalis

contamination risk for foods that do not undergo any further processing, such as sandwiches and salads.

Good personal hygiene practice, especially

hand washing

, is an essential control .

Any

staff suffering from gastroenteritis should be excluded from processing areas.Slide23

Legislation

It is not usually mentioned specifically in food safety and hygiene law.