Malaria transmission begins when a female mosquito bites a human already infected with the malaria parasite. The mosquito ingests blood containing immature male and female gametes (sex cells) of the malaria parasite. Inside the mosquito’s stomach, the gametes quickly mature. A male gamete fuses with a female gamete to produce a cell known as a zygote. The zygote enters the wall of the mosquito’s gut and develops into an oocyst. The oocyst multiplies to produce thousands of cells known as sporozoites. The sporozoites leave the wall of the gut and migrate to the mosquito’s salivary glands. The mosquito phase of the malaria parasite’s life cycle is normally completed in 10 to 14 days. This development process occurs more slowly in areas with cooler temperatures. Sporozoite development of Plasmodium falciparum is slowed particularly by low temperatures, preventing transmission of this parasite in temperate climates except during summer.
When the infected mosquito bites another human, sporozoites in the mosquito’s saliva transfer to the blood of the human. Sporozoites travel in the blood to the liver. In liver cells over the course of one to two weeks, the sporozoites divide repeatedly to form 30,000 to 40,000 merozoites. The merozoites leave the liver to enter the bloodstream, where they invade red blood cells. Inside these blood cells, the merozoites multiply rapidly until they force the red cells to burst, releasing into the bloodstream a new generation of merozoites that go on to infect other red blood cells. Some merozoites divide to form gametocytes, immature male and female gametes. If another mosquito bites the human and ingests these gametocytes, the life cycle of the malaria parasite begins again.
Symptoms
The fever that characterizes malaria develops when merozoites invade and destroy red blood cells. The destruction of red blood cells spills wastes, toxins, and other debris into the blood. The body responds by producing fever, an immune response that speeds up other immune defences to fight the foreign invaders in the blood. The fever usually occurs in intermittent episodes. An episode begins with sudden, violent chills,
soon followed by an intense fever and then profuse sweating that brings the patient’s temperature down again. Upon initial infection with the malaria parasite, the episodes of fever frequently last 12 hours and usually leave an individual exhausted and bedridden. Repeated infections with the malaria parasite can lead to severe anaemia, a decrease in the concentration of red blood cells in the bloodstream. The malaria parasite consumes or renders unusable the proteins and other vital components of the patient’s red cells.
The pattern of intermittent fever and other symptoms in malaria varies depending on which species of Plasmodium is responsible for the infection. Infections caused by Plasmodium falciparum, Plasmodium vivax, and Plasmodium ovale typically produce fever approximately every 48 hours, or every first and third day. Infections caused by Plasmodium malariae produce fever every 72 hours, or every fourth day.
Infections caused by Plasmodium falciparum are marked by their severity and high fatality rate. This type of malaria can also cause severe headaches, convulsions, and delirium. The infection sometimes develops into cerebral malaria, in which red blood cells infected with parasites attach to tiny blood vessels in the brain, causing inflammation and blocking the flow of blood and oxygen. In Plasmodium vivax and Plasmodium ovale infections, some merozoites can remain dormant in the liver for three months to five years. These merozoites periodically enter the bloodstream, triggering malaria relapses.
Aphids
Aphids feed by sucking sap from the plant, distorting its growth. This may mean that new shoots are stunted, leaves cannot photosynthesise very effectively, or fruit is disfigured and fails to mature properly.
They also excrete shiny, sticky honeydew as a waste product which can cover leaves, encouraging the growth of black sooty mould. This is unsightly and may further damage the plant's health by blocking out the light it needs. Aphids are also responsible for spreading many virus diseases.
Butterflies
Butterflies and most moths feed through a tube-like tongue called a proboscis so their food must be liquid. Many feed on nectar from various flowers while others feed on a variety of moist rotting matter including, fruit, sap, animals, and animal droppings. Some butterflies will also visit mud puddle to sip nutrients from soil.
Houseflies
Houseflies can only ingest liquid food. The mouth parts of a house fly are adapted for sponging up liquids; they cannot bite. They feed on solid food by regurgitating saliva on it. This liquefies the solid material which is then sponged up.
(B) FEEDING IN MAMMALS
(1) Teeth.
Teeth, hard, bony structures in the mouths of humans and animals used primarily to chew food, but also for gnawing, digging, fighting, and catching and killing prey. Teeth are the body’s hardest, most durable organ—long after bones and flesh have dissolved; archaeologists find well-preserved teeth from humans and other animals that lived thousands of years ago.
Humans use teeth to tear, grind, and chew food in the first step of digestion, enabling enzymes and lubricants released in the mouth to further break down food.
Teeth also play a role in human speech—the teeth, lips, and tongue are used to form words by controlling airflow through the mouth. Additionally, teeth provide structural support to muscles in the face and form the human smile.
Like humans, most animals use their teeth to chew food, although many animals have evolved teeth that perform other specialized tasks. For example, many carnivorous (meat-eating) animals, such as tigers, have developed long, sharp teeth for clamping down on and killing prey. Beavers have chisel-like front teeth that they use to cut down large trees for building dams.
Dogs have teeth and jaws that are adapted for a carnivorous diet: the incisors are small and can be used to pull meat apart;
- the canines are sharp and pointed and may be used to grip prey, as
- well as for tearing meat;
- the premolars and molars include special large carnassials teeth
- which can be used to shear meat and crush bones;
- The jaws move only up and down in order to provide a firm scissor action.
(2).
The digestive systems of mammals are adapted to the diet consumed in various ways such as the type of food that is being digested, bacteria and enzymes. Below is information on different mammals and their digestion.
a). Mammals.
Do mammals have enzymes for cellulose digestion?
Mammals cannot digest cellulose because a mammal does not contain the necessary enzyme in the body which will break down the cellulose. This means that a mammal cannot get energy from the cellulose. However, it still has a useful function: it is the main source of dietary fibre (roughage) this keeps food moving along the Oesophagus and helps to prevent constipation.
Fibre, a form of dietary carbohydrate, contains cellulose. Cellulose is a structural component of plant structure and is resistant to human digestive enzymes. Cellulose can be excreted in the faeces; however some of it is fermented by the bacteria present in the large intestine. Much like yeast are used to ferment the sugars in grape juice to produce wine, the bacteria in our large intestine ferment cellulose to produce hydrogen and carbon dioxide gases, volatile fatty acids and in many instances, methane gas (which has an unpleasant odour). Changes in the diet or in the type of micro organisms can influence the amount of gas produced.
b). Sheep and Cows
What is rumen and does it contain bacteria?
Sheep and cows have a rumen between the oesophagus and stomach which contains these bacteria. To enhance digestion, part-digested material from the rumen is re-chewed in the mouth. Ruminant digestion is a way of protecting cattle, deer, sheep, and goats. The digestion in the rumen actually provides warmth for the animal. The rumen is basically a huge fermenting vat. A microbial population (bacteria and protozoa) digests (or more correctly ferments) the feeds eaten by the animal. The inside of the rumen wall has millions of tiny "finger like" projections called papillae. These papillae act to increase the surface area of the rumen, thus giving the rumen maximum contact with its contents. Rumen development results from Volatile Fatty Acids (VFA) in the rumen. For good digestion a good blood supply to the rumen papillae is needed.
Bacteria start "arriving" in the rumen shortly birth. Useful bacteria however occur as the result of the calf eating dry feed. True ruminant bacteria can be found about 14 days after calves start eating "early wean", or "starter" pellets, or meal. The rumen micro organism's change ingested carbohydrates into Volatile Fatty Acids (VFA), acetate, propionate, and butyrate. Propionate and butyrate are the two Volatile Fatty Acids responsible for the rumens development. Rumen Volatile Fatty Acids are absorbed from the rumen. The food eaten affects the types of rumen micro organisms
active in the rumen. E.g. calves fed early wean pellets will establish a different bacteria from those fed mainly hay. Rumen bacteria need a warm watery environment.
c). Rabbits
Rabbits have cellulose-digesting bacteria in a large appendix /caecum which opens into the junction between the small and large intestines. Because the food that is digested here has already passed through the small intestine, rabbits eat their own faeces.
d). Carnivores
Strict carnivores
For most purposes, we are talking about the cat family, some aquatic mammals, fish, and some birds here. As discussed before, strict carnivores rely on the direct conversion of meats and fish into living tissue and have little need for complicated interplay involving diet and the gut micro flora. Strict carnivores also have lost the ability to produce other metabolic compounds that are commonly synthesized by herbivores and omnivores. This may complicate things when it comes to formulating an artificial diet for these animals. For example, a sulphur-containing amino acid known as taurine is "essential" (meaning it must be supplied in the diet) for cats. This amino acid is not available in plants and thus herbivores have developed metabolic pathways to produce it when needed. However, cats have not needed to synthesize taurine since it is readily available in herbivore meat. If taurine is absent from the diet, cats will become ill and eventually succumb to nutrition-related disorders. Thus, although we may be able to meet some needs of strict carnivores through plant or cereal-based diets, a certain amount of meat material remains essential, and at least for the time being, herbivores will be "asked" to give up their taurine and other essential compounds for carnivore diets. Additionally, many other animals, including herbivores and omnivores cannot produce taurine when very young, depending instead on the taurine available in their mother's milk.
Carnivores have no need for cellulose-digesting bacteria, and their digestive system does not have special sections to contain them.
e). Herbivores
The relationship between cellulose-digesting bacteria and herbivores is an example of mutualism as both organisms benefit from living together. The herbivores obtain sugar from the cellulose, and the bacteria get a supply of cellulose and other nutrients.
Foregut fermenters
These animals include deer, sheep, and bovines (true ruminants), camels, peccaries, hippos, kangaroos, leaf-eating monkeys, languor’s, some rodents, leaf-eating sloth’s and others. Foregut fermenters posses one or more large holding organs ahead of the gastric organ (true stomach). They consume diets that contain vast quantities of cellulose and other fibrous materials that are much more limited in readily-useable carbohydrates and protein than food consumed by carnivores. While energy can be derived from cellulose, animals do not produce the enzymes necessary for the breakdown of these materials. Fermenters therefore rely on bacteria residing in the special fermentation organs to break down the cellulose. In this anaerobic environment, the bacteria consume the plant material for their own metabolic needs and, as a result, produce end-products of fermentation called volatile fatty acids (VFA). VFA, including acetate, propionate, and butyrate are readily absorbed by the tissues of the fore- and hindgut and are used as an energy source by the herbivore.
