Transmission of Transmission of pathogens and prevention pathogens and prevention

of infectionof infection

By Tracy Wong

Yuki Kong

What is pathogen?

Microorganisms that cause disease and are considered a nuisance( 損害 ). These may either be a virus, bacterium or fungus.

The routes of transmission of pathogens:

-air ( e.g. common cold, influenza 流行性感冒 )

- water or food ( e.g. cholera 霍亂 )

- vector (e.g. malaria 瘧疾 )

- body fluids ( e.g. hepatitis B B 型肝炎 , AIDs)

Air common cold

A common cold is an illness caused by a virus infection located in the nose

Transmission of Disease

Contact– Direct Requires close association betwee

n infected and susceptible host

– Indirect Spread by fomites– Droplet Transmission via airborne

droplets

Transmission of Disease

Transmission of Disease

Vehicle Transmission by an inanimate( 無生命的 , reservoir (food, water)

Vectors Arthropods 節足動物 , especially fleas 蚤 , ticks 寄生蠅 , and mosquitoes

Mechanical Arthropod carries pathogen on feet

Biological Pathogen reproduces in vector

Transmission of Disease

The appearance of the virions, Virions are 42nm in diameter and p

ossess an isometric nucleocapsid or "core" of 27nm in diameter, surrounded by an outer coat approximately 4nm thick. The protein of the virion coat is termed "surface antigen" or HBsAg. It is sometimes extended as a tubular tail on one side of the virus particle. The surface antigen is generally produced in vast excess, and is found in the blood of infected individuals in the form of filamentous and spherical particles. Filamentous particles are identical to the virion "tails" - they vary in length and have a mean diameter of about 22nm. They sometimes display regular, non-helical transverse striations.

How does a baby get hepatitis B from his or her mother?

They will get the disease only if the mother has hepatitis B and a tiny bit of their mothers’ blood gets inside the baby at birth.

Can the mother breast-feeds her baby if she has hepatitis B?YES! If the mother’s baby gets a shot called H-BIG and a shot of hepatitis B vaccine within 12 hours of birth, it is okay for the mother to start breast-feeding her baby right away. Be sure to take good care of her nipple areas to prevent cracking and bleeding.

Transmission by food and water

CryptosporidiumCryptosporidium (crip-toe-spor-ID-ee-um) is a protozoan, a single-celled parasite, that lives in the intestines of animals and people. This microscopic pathogen causes a disease called cryptosporidiosis (crip-toe-spor-id-ee-O-sis.The dormant (inactive) form of Cryptosporidium, called an oocyst (O-o-sist), is excreted in the feces (stool) of infected humans and animals. The tough-walled oocysts survive under a wide range of environmental conditions.

The appearance of the pathogen: Cryptosporidium parvum is a small,

crude and potentially deadly pathogen.cryptosporidium sickened more than 13,000 people in Carrolton, Ga. Scientists traced the outbreak back to the municipal water supply – surprising, considering that the water met all state and federal safety standards."It can exist outside its host in a tough egg-type structure called an oocyst, which can cause infection once it’s been ingested by humans and host species," he adds.Equally disturbing, Hairston says, is the fact that scientists are not sure how long these oocysts can survive under a wide range of environmental conditions.

How is the pathogen spread?You can get infected with Cryptosporidium when you put anything in your mouth that has been in contact with feces from an infected animal or person. When large numbers of people get cryptosporidiosis, the source of infection can sometimes be tracked down, but it is impossible to determine the origin of many individual cases of this disease. Your hands may be contaminated with Cryptosporidium through person-to-person contact, perhaps while changing a child's diaper, caring for someone with diarrhea or engaging in any activity that involves touching areas of the body contaminated with feces. Cryptosporidiosis can be easily spread among people in close social groups such as families, day care centers, and nursing homes. People who work with animals, especially young animals or animals with diarrhea, have greater chance of exposure to the parasite. You may pick up oocysts while handling soil, or any object contaminated with even a small amount of feces.

You can also get cryptosporidiosis by drinking water or eating food that has been contaminated with oocysts. Drinking untreated surface water (such as streams, rivers, and lakes) or swallowing a small amount of water when swimming, even in a chlorinated pool, can cause cryptosporidiosis. The parasite may also be spread in uncooked foods, beverages, or ice prepared with contaminated water. Unwashed fresh fruits or vegetables may carry oocysts if manure was used or animals grazed where the crop was grown. People who are infected (or whose hands become contaminated) with Cryptosporidium can spread the disease to other people or pets if they are not careful about their hygiene. Frequent handwashing is the single most important thing people can do to avoid spreading cryptosporidiosis and other illnesses. It is especially important to wash thoroughly before preparing food, as well as after using the toilet.

How can we prevent the disease?We can protect our water supplies from Cryptosporidium. Multiple barriers are needed to protect our water supplies from Cryptosporidium. Water treatment methods alone cannot solve the problem; watershed protection and monitoring of water quality are critical.

The life cycle of cryptosporidi