Tuesday, June 24, 2014

Parasites And Disease

Parasites And Disease
Parasite is any organism that lives at the expense of another (host) organism. Some

parasites carry or cause disease.



Parasites are a world-wide major health problem ranking amongst the greater threats to

the well being and survival of mankind. Parasites occur in all natural communities,

sometimes as benign infections, but they may also have massive economic impact by

seriously damaging populations of domestic animals, fish and crop plants. Continuous

effort by the world community of parasitologists is necessary to understand and further

the control of parasites and their vectors.



Parasitic infections are acquired by eating or drinking contaminated food or water,

through direct contact with soil or water containing parasites or their larva, or by

contact with biting insects.



The blood feeding mode evolved independently more than 150 million years ago in at

least 6 different groups of arthropods. These arthropods (insects and ticks), had to solve

independently the problem of how to deal with their hosts' defense against blood loss, the

hemostatic mechanism. Fifty million years ago, dinosaurs went extinct and mammals became

the main food source, bringing with it a new problem posed by blood platelets, which are

much more efficient then bird or reptile (or dinosaur) thrombocytes in preventing blood

loss. Blood feeding arthropods even in the same family had to discover new pharmacological

products to deal with this new feeding problem. Perhaps because of these evolutionary

reasons, a very large diversity of pharmacological products are being discovered in the

saliva of such arthropods, which comprise around 15,000 species in near 600 genera.



Despite decades of concerted international efforts, malaria remains the most

devastating insect-borne parasitic disease of man and until now no acceptable measures has

been devised that can eradicate this killer disease. Because malaria parasite's

development in the mosquito is obligatory, our goal is to disrupt the development of the

parasite in the vector to block the transmission to human.



During the complex development of malaria parasites in mosquitoes new sets of genes are

sequentially expressed in the parasite. Similarly, after blood feeding the biochemical

environments in the mosquito changes dramatically. For successful development and

tranmission to human, malaria parasites must interact with numerous biochemical and

physical factors in the mosquito .



Scientists today are working not only to develop new vaccines against diseases that

still make people sick, but they also are searching for unique ways to get vaccines into

people.



A new approach to malaria is to develop a vaccine that prevents transmission of the

malaria parasite from one infected person to another person. This type of vaccine would be

given to people already infected with the parasite--not to protect them from illness but

to prevent the parasite from infecting someone else.



After a mosquito bites a person whose blood contains the malaria parasite, the mosquito

normally transmits the parasite to someone else when it next feeds. But this vaccine would

block the sexual development of the parasite in the mosquito, so that the parasite could

not cause malaria in the next person bitten by the mosquito.



Other parasites include Giardia lamblia, which is a major cause of intestinal disease

worldwide and the most frequent non-bacterial cause of diarrhea in North America.

Nonetheless, the basic biology of this parasite--including how it ravages the digestive

tract--is poorly understood.



Giardiasis affects three times more children than adults, particularly diapered

children and toddlers being toilet-trained. Families with young children who attend

day-care centers are at greater risk of developing giardiasis than is the general

population.



The usual interval between infection and the onset of acute symptoms ranges from one to

two weeks. In most instances, the individual will experience sudden explosive, watery,

foul-smelling diarrhea; excessive gas; abdominal pain; bloating; nausea; tiredness; and

loss of appetite. Upper gastrointestinal symptoms such as vomiting may predominate. Fever

is unusual. Many infected people, however, have very mild symptoms or no symptoms at all.

Blood or mucus in the stool rarely occurs. Occasionally, the illness may last for months,

or even years, causing recurrent mild or moderate symptoms such as impaired digestion,

especially lactose intolerance; intermittent diarrhea; tiredness and weakness; and

significant weight loss.



Presently, there is no drug available to prevent giardiasis. The following precautions

should be taken if visiting an area where Giardia may exist: drink only boiled or filtered

water, or bottled carbonated drinks; avoid ice and beverages made from tap water; and do

not eat uncooked or unpeeled fruits and vegetables grown locally.



Parasites (in the larval stage) consumed in uncooked, or undercooked, unfrozen seafood

can present a human health hazard. Among parasites, the nematodes or roundworms (Anisakis

spp., Pseudoterranova spp., Eustrongylides spp. and Gnathostoma spp.), cestodes or

tapeworms (Diphyllobothrium spp.) and trematodes or flukes (Chlonorchis sinensis,

Opisthorchis spp., Heterophyes spp., Metagonimus spp., Nanophyetes salminicola and

Paragonimus spp.) are of most concern in seafood. Some products that have been implicated in human infection are:





  • ceviche (fish and spices marinated in lime juice)


  • lomi lomi (salmon marinated in lemon juice, onions and tomato)


  • poisson cru (fish marinated in citrus juice, onions, tomatoes

    and coconut milk)


  • salmon roe


  • sashimi (chunks of raw fish)


  • sushi (pieces of raw fish with rice and other ingredients)


  • green herring (lightly brined herring)


  • drunken crabs (crabs marinated in wine and peppers)


  • cold-smoked fish and,


  • undercooked grilled fish




The process of heating raw fish sufficiently to kill bacterial pathogens is sufficient

to kill parasites.



Freezing (-4F)(-20C) or below (internal or external) for 7 days or -31F

(-35C) or below (internal) for 15 hrs) of fish intended for raw consumption also

kills parasites. FDA's Food Code recommends these freezing conditions to retailers who

provide fish intended for raw consumption.



Brining and pickling may reduce the parasite hazard in a fish, but they do not

eliminate it, nor do they minimize it to an acceptable level. Nematode larvae have been

shown to survive 28 days in a 80 degree F salimeter brine (21% salt by weight).



Trimming away the belly flaps of fish or candling and physically removing parasites are

effective methods for reducing the numbers of parasites. However, they do not completely

eliminate the hazard, nor do they minimize it to an acceptable level.






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