Parasitic wasps Essay

This essay has a total of 5670 words and 29 pages.

Parasitic wasps



Introduction

Malaria is one of the most prevalent and dangerous diseases known to man. It has existed
for centuries and affects a myriad of people in the tropical region. Even today, with our
newly discovered treatments for many of the tropical diseases, over 10% of the people that
are infected with malaria each year and do not receive proper treatment die. In Africa
alone, over 1 million children die each year because of malaria and new cases are reported
frequently. Malaria is very dangerous and harmful to man.



However, the protozoan that causes malaria has existed since man came into being. Fossils
of mosquitoes that are 30 million years old contain the vector for malaria. After written
history, many civilisations have known about malaria. The Greek physician Hippocrates
described the symptoms of malaria in the 5th Century BC The name malaria is derived from
the Italian words, mal and aria, meaning "bad air", because people of earlier times
believed that the disease was caused by polluted air near swaps and wetlands in Europe.
The scientific identification of malaria was not found until 1880. The French army
physician, Charles Laveran, while stationed in Algeria, noticed strange shapes of red
blood cells in certain patients and identified the disease scientifically and linked to a
certain protozoan. Although the disease had been identified, it was not until 1897, when
British army physician, Ronald Ross studied birds and discovered that the malarial
protozoan was transmitted through mosquitoes. Soon after, two Italian scientists noted
that mosquitoes spread malaria to humans as well. Many attempts have been made to try to
eradicate the disease. As early as 7 AD, in Rome, swamps were drained to try to prevent
the "bad air" from reaching nearby cities. Recently, in the 1950's and 1960's, about 25
years after the development of DDT, the United Nations World Health Organisation tried to
wipe out the disease through the use of DDT. Although, the number of cases was reduces in
many areas, they started again. Scientists today believe that malaria can never be
eradicated due to the fact that the protozoan can manipulate easily and become resistant
to a drug that is overused. The mosquitoes that spread malaria are also becoming resistant
to insecticides. Malaria can be treated on an individual basis and treatments and
medicines can be used.

To understand these treatments however, one must understand what happens to a malarial
protozoan. The disease, malaria, is cause by the protozoan, Plasmodium, which lives in
tropical regions all around the world. There are only four species of this protozoan that
cause malaria in humans, Plasmodium ovale, Plasmodium vivax, Plasmodium malariae, and
Plasmodium falciparum. These protozoans are spread from infected to healthy people through
the bite of the Anopheles mosquito, blood transfusions, or through hypodermic injections.
This makes malaria one of the most easily communicable diseases in the world.



1.Sporozoites in salivary gland.
2.O÷cysts in stomach wall.
3.Male and female gametocytes.
4.Liver phase.
5.Release of merozoites from liver.
These enter red cells where both sexual and asexual cycles continue.


Malaria is spread only through the females of the 60 different types of the Anopheles
mosquito, as the males do not feed on blood. The symptoms of this disease are many,
however a physician must be consulted to avoid risk to a person.

To treat malaria, many drugs are used today. Forms of these drugs date back to the 1500's
and 1600's. Physicians diagnose malaria by identifying Plasmodia in a patient's body. Once
identified, malaria can be treated with chloroquine and primaquine. Since some forms of
Plasmodia falciparum have become resistant to these, quinine, mefloquine, or halofautrine
are used. Almost all of the cases of malaria can be treated if done in the proper way.
However, to suffer the pain and illness of malaria, people can use many preventive
measures. All swampy areas must be avoided as well as tropical water that may be
contaminated or local food. People should just protect themselves from mosquitoes and risk
of infection will be tremendously lowered. This can be done by impregnated bednets. These
involve surrounding the bed with a curtain that is sprayed with certain compounds. These
are normally pyrethroids or organophosphates, which create an effective barrier between
the mosquito and its blood meal. Alternative 'barrier' methods are insect repellents.
These are certain chemicals that that when applied to the skin as a spray or lotion is
quite effective at deterring the mosquito from landing on a person in order to feed.

Other methods of controlling malaria are the use of insecticides and vaccines.
Insecticides are chemicals such as pyrethrum, which are sprayed within persons living
quarters. This was thought to kill the female mosquito preventing it from spreading
malaria and laying further eggs as long as it had no means from escaping the room before
spraying. Vaccines work by stimulating antibody production to destroy a foreign organism
in the body. As the foreign organism has the same surface antigens as the pathogenic
organism, the antibody that the body produces to destroy the antigenic material in the
vaccination will be equally as effective against the pathogenic organism. The lymphocytes
that produce the antibody will remain in the blood stream. When the pathogenic organism
enters the body the lymphocytes will be triggered to produce the antibody in order to
destroy the invading organism. At the moment this is where a lot of malaria research is
centred - in trying to produce a malaria vaccine.

Man evolved as a hunter-gatherer, with populations of low densities compared with other
primates. At these low densities man would not have been the preferred host of many
parasites, but would have experienced malaria as a zoonosis. It is postulated that the
development of agriculture around 10,000 to 7000 years ago resulted in man made changes in
nutrition, the environment and population density. These changes are so recent in genetic
terms that the species has not adapted. The success of our species, expressed as
population expansion, has been at the cost of widespread disease, of which malaria related
diseases are common manifestations. The burden is heaviest on pregnant women and children
under five years old.

Over 8 million of the 13 million under-five deaths in the world each year can be put down
to diarrhoea, pneumonia, malaria, and vaccine-preventable diseases. But this simple way of
classifying hides the fact that death is not usually an event with one cause but a process
with many causes. In particular, it is the conspiracy between malnutrition and infection,
which pulls many people into the downward spiral of an early death and poor growth in
children. Now, a new study has attempted to quantify the role of malnutrition in child
deaths. Using data from 53 developing countries, researchers from Cornell University have
concluded that over half of those 13 million child deaths each year are associated with
malnutrition. Further, they show that more than three-quarters of all these
malnutrition-assisted deaths are linked not to severe malnutrition but to mild and
moderate forms.

This suggests that nutrition programmes focusing only on the severely malnourished will
have far less impact than programmes to improve nutrition among the much larger number of
mildly and moderately malnourished children. As discussed in the 1994 edition of The
Progress of Nations, low-cost methods of reducing all forms of malnutrition are available
and have been shown to work. And action on both fronts - to improve nutrition and to
protect against disease - could save many more lives (and be far more cost-effective) than
action on either front alone.

Malnutrition receives few banner headlines, like the AIDS crisis does. There is no excuse
for starvation, with technology and science making food as plentiful as it is. Yet famine
and malnutrition are not the same thing. Many of these children may be getting food. But
what are missing are the nutrients they need to grow into healthy and productive adults. A
report by UNICEF indicates that at least 100 million young children and several million
pregnant women have damaged immune systems not because of HIV or AIDS, but because of
malnutrition

It is thought that malaria can be prevented and risk of infection lowered with varies
nutritional aspects. These include minerals such as Iron, zinc and Vitamins A, C, D, E,
antioxidants, fatty acids and carbohydrates. Over the years, as the control of diseases
such as malaria has improved, the significance of malnutrition has emerged more clearly.
There is a need to understand its cause to ensure secure foundations for schemes of
prevention, and thus preventing disease. Nutrition and many tropical infections such as
malaria interact, not just because of extensive geographical overlap between areas where
malaria occur or nutrient deficiencies are common. The clinical and public health
implications and the range of such interactions are becoming increasingly appreciated. It
is evident that in many countries malnutrition is responsible for the high mortality in
children along with disease. It is with children and pregnant women particularly that most
of the research with nutrition and malaria has been done.

Malaria is truly a grave problem and could affect any ignorant person. However, if a
person takes certain precautions and does not get involved with insects, they might just
be safe from being one of the 300,000,000 people who are infected each year, or even
worse, one of the 1,500,000 people that die of malaria annually.



Recommended Daily Allowances

Most people are familiar with the Recommended Daily Allowances (RDA) for vitamins and
minerals that have been established by the Food and Nutrition Board of the National
Research Council. The RDA is defined as the level of intake of an essential nutrient that
is judged to be adequate to meet the known needs of healthy people. At these levels, in
other words, people should not develop the deficiency illness associated with a lack of
that nutrient.

The RDA does not apply to people with special nutritional needs, nor does it suggest that
these are the optimal dietary levels for these nutrients for normal people. We now know
that mild to moderate deficiency of basic nutrients, while not causing the classic
deficiency illnesses, may contribute to a host of other illnesses, especially in today's
world, where stress and poor lifestyle habits may tax the body's nutritional resources.
Scientific data suggest that the consumption of many nutrients above the RDAs may prevent
or combat many common illnesses.









Nutrient RDA Sources
Vitamin A 10,000 IU
Vitamin B1 (Thiamine) 1.5 mg
Vitamin B2 (Riboflavin) 1.7 mg
Vitamin B3 (Niacin) 20 mg
Vitamin B6 (Pyridoxine) 2 mg
Vitamin C 60 mg citrus fruits, strawberries, tomatoes, cantaloupe, broccoli, asparagus, peppers, spinach, potatoes
Vitamin D 400 IU
Vitamin E 30 IU vegetable oils (soy, corn, olive, cottonseed, safflower, and sunflower),
nuts, sunflower seeds, wheat germ.

Beta Carotene 15-50 mg dark green, yellow, and orange vegetables including spinach,
collard greens, broccoli, carrots, peppers, and sweet potatoes; yellow fruits such as
apricots and peaches.


Folic Acid 0.2 mg
Iron 15 mg
Zinc 15 mg

(IU = international units; mg = milligrams)
Micronutrients

Investigations into interactions between nutrient status and infectious disease are
seriously complicated by the difficulties of assessing status of many nutrients during the
acute phase response to infection. Many nutrients are acute phase reactants for example,
plasma retinol, zinc and iron and the degree of transferrin saturation all decrease, and
plasma copper and ferritin and erythrocyte protoporphyrin increase, in response to
infection or trauma (Filteau, S M, and Tomkins, A M, 1994). There is an urgent need for
research into nutritional assessment of infected individuals and populations since these
are frequently the people whose nutritional status is of most concern. The consistent
alterations of micronutrient metabolism suggests that these may have advantages in the
fight against infection, the alterations in iron metabolism have been suggested as a means
of pathogen replication (Thurnham, 1990). The redistribution of zinc to liver and bone
marrow after infection of inflammatory cytokines may serve to support acute phase protein
synthesis and haematopoesis. Patients with chronic inflammatory conditions have increased
concentrations of zinc in mononuclear leukocytes, which may indicate that cells of the
immune system are also favoured for zinc during inflammatory responses. The potential
benefits of retinol fluxes during infection have not been explored. Although it is clear
that a decreased plasma concentration of a nutrient during infection may be a beneficial
adaptation rather than a harmful deficiency (Filteau, S M, and Tomkins, A M, 1994). The
problems of assessing nutrient status during infection have made it difficult to determine
whether infections decrease status itself over the long term. Several factors could
contribute to impaired status, including decreased appetite, decreased absorption due to
diarrhoea, or increased requirement for nutrients for immune functions or tissue repair.




Vitamin E

Neither the American Heart Association nor professional medical societies endorse vitamin
E supplements, though, mainly because most of the published research is observational. To
date, there have only been two controlled clinical trials evaluating vitamin E.

There is some evidence that vitamin E (a-tocopherol) plays a role in the development of
malaria infection. The malaria parasite is sensitive to oxidant stress and antioxidant
agents such as Vitamin E may potentiate the infection in vivo (Skinner-Adams, T, et al
1998). Addition of vitamin E to cultures in vivo has been found to improve the growth of
Plasmodium falciparum in old, normal red blood cells. In addition vitamin E deficient mice
are resistant to Plasmodium Yoelii infection, while low serum vitamin E levels in humans
with falciparum malaria are associated with a relatively short parasite clearance time.
Vitamin E like any other antioxidant vitamins also behave as a pro-oxidant under certain
conditions and may therefore paradoxically inhibit the growth and development of malaria
parasites at high blood concentrations.

In a study results showed that vitamin E has limited ability to influence the growth of
P. falciparum in vivo at medium concentrations, which span and exceed those present in
normal blood serum (Skinner-Adams, T, et al 1998). Some inhibitory activity was seen at
concentrations equivalent to the upper limit of normal human plasma concentrations.
Subphysiological vitamin E concentrations may, through increasing oxidant stress and
perhaps membrane effects which impair merozoite invasion, inhibit the development of P.
falciparum in humans. At supraphsiological concentrations, vitamin E behaves as a
pro-oxidant and inhibition is seen. As malaria infection is associated with depressed
serum vitamin E concentrations in humans, the maintenance of relatively high oxidant
stress environment should aid in the treatment of malaria. Although treatment with vitamin
E may have an unpredictable effect on parasite burden, reflecting factors such as dose,
pre-treatment plasma concentrations, and liver stores. Due to this, supplementation with
vitamin E may not be appropriate in the acute phase of the illness.



Vitamin A (Beta-carotene, Retinol)

Beta-carotene is a previtamin-A compound found in plants. The body converts beta-carotene
to vitamin-A. Vitamin A can be found in fresh apricots, asparagus, broccoli, cantaloupe,
carrots, endive, kale, leaf lettuce, liver, mustard greens, pumpkin, spinach, squash,
winter, sweet potatoes and watermelon. Vitamin A has many beneficial uses it; 1) Aids in
treatment of many eye disorders, including prevention of night blindness and formation of
visual purple in the eye; 2) Promotes bone growth, teeth development, reproduction; 3)
Helps form and maintain healthy skin, hair, mucous membranes; 4) Builds body's resistance
to respiratory infections; 5) Helps treat acne, impetigo, boils, carbuncles, open ulcers
when applied externally.

It is thought that the vitamin helps in shorting the duration of illnesses and helps in
fighting infection. Vitamin A deficiencies may also lead to diarrhoea a malaria related
diseases.


Clinical vitamin A deficiency in children, although still of public health significance in
many countries, currently are rare in the United States and other industrially developed
countries. Whereas clinical vitamin A deficiency is becoming less common in less
industrialised countries, subclinical deficiency, also termed marginal vitamin A status,
is still prevalent. In this regard, the incidence of mortality among pre-school children
in many less industrialised countries is reduced by approximately 30% when vitamin A
supplements are provided.


Each year, vitamin A deficiency contributes to the deaths of between 2 and 3 million
children, to approximately 500,000 cases of permanent blindness, and to increased
morbidity for many adults, especially among pregnant women. Vitamin A deficiency in
children is common in countries where rice is a primary food staple.

With support from The Micronutrient Initiative, PATH completed a feasibility study on the
introduction of vitamin A-fortified Ultra Rice in the rural province of East Nusa Tenggara
Timur in Indonesia. The project was implemented by PATH, several local national government
officers (NGOs), and Bon Dente Nutrition, a private company involved in the development of
food products and fortificants. The trial verified the stability of vitamin A under field
conditions, validated a mixing procedure for small rice millers, demonstrated consumer
acceptability of the product, and confirmed the feasibility of selling vitamin A-fortified
rice in local outlets. Furthermore, the trial attracted national, provincial, and local
government interest in fortification of rice.


Malaria Morbidity in Young Children
Vitamin A is often deficient in individuals living in malaria endemic areas, is essential
for normal immune function, and several studies show it could play a part in potentiating
resistance to malaria. Studies have shown that vitamin A deficient rats and mice are more
susceptible to malaria than normal animals, and this susceptibility is readily reversed by
vitamin A supplementation. Also, a genetic locus, which includes cellular retinol-binding
protein, influences malaria mortality and parasitemia in mice. In vitro, addition of free
retinol to P.falciparum cultures reduced parasite replication in one study but not in
another (Shankar A H, et al 1999). In humans there has been evidence for the role of
protective vitamin A but it has not been proven. Although cross sectional studies with
children and adults have shown that low plasma vitamin A concentrations are associated
with increased blood parasite counts. However increased parasite counts can trigger an
acute phase response, which transiently depresses the circulating vitamin A concentration.
The number of episodes of falciparum malaria among children in Papua New Guinea was 30%
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