Infectious diseases -Malaria

• malaria is caused by a single celled organism called
• the organism is transmitted from one person to another by female anopheles mosquito.
• a mosquito takes up the gametes of a malaria parasite when it feeds on the blood of an infected person.
• fertilisation occurs in the stomach of the mosquito and the immature parasites reproduce.
• infective stages of the malaria parasite migrate to the mosquito‘s salivary glands.
• a new person becomes infected when the mosquito takes another meal of the infected blood.
• the parasites enter the liver of the new victim where further reproduction takes place before migrating to the red blood cells.
• when an organism such as mosquito is involved in transmission, it is called a vector. –    the malarial parasite can also be transmitted by a vector

 

 

Transmission of malaria

Explain how an infected is likely to have acquired malaria

• bitten by mosquito carrying malarial parasite;
• genus Anopheles/female;
• injects parasites with saliva/anticoagulant;
• ref to vector;
• mosquito fed on/bit/took a blood meal from an infected person;
• transmission by needle;
• injected into blood;
• after use by someone with malaria;
• (needle) shared/reused/used but not sterile;
• Transmission across placenta;
• Blood transfusions;

 

Signs and symptoms of malaria

People with malaria have the following symptoms:

• abdominal pain.
• chills and sweats.
• diarrhea, nausea, and vomiting (these symptoms only appear sometimes) –
• high fevers.
• low blood pressure causing dizziness if moving from a lying or sitting position to a standing position (also called orthostatic hypotension)

 

Ways of preventing the spread of malaria

Explain the ways in which the transmission of the malaria life cycle can be disrupted

reduce mosquito numbers 

• stock ponds with fish (Gambusia) to eat larvae ; R kill mosquitoes
• oil on surface ;
• spray bacteria (Bacillus thuringiensis) to kill mosquito larvae ;
• DDT / pesticide spray ;
• release of sterile male mosquitoes ;
• draining, ponds / bodies of water ;

 

Avoid being bitten by mosquitoes

• wear insect repellant ;
• long sleeved clothes ;
• sleep under nets ;
• nets soaked in, insecticide / repellant ;
• sleep with, pigs / dogs ;

 

use drugs to prevent infection

• use, prophylactic drug / quinine / chloroquine / larium / artimesinin / vibrimycin/ tetracycline / antimalarial.
• use malaria vaccine ;

 

Social and biological factors in the prevention of malaria

Social

• poverty;
• no access to treatment/access to anti-malaria drugs;
• no access to mosquito nets/sleep under mosquito nets
• cultural beliefs

 

Biological

• Plasmodium strains resistant to some malaria drugs such as chloroquine
• development of resistance in Plasmodium/breaking life cycle of vector;
• development of resistance to pesticide;
• use of natural predators of vectors;
• some pesticides extend their effects to other innocent organisms;
• vaccination failing;
• Plasmodium an intracellular pathogen;
• an enormous reserve in monkeys;
• Plasmodium antigens change from time to time making vaccination difficulty;

 

Outline the problems associated with controlling the spread of malaria

• resistance of, Plasmodium / pathogen, to drugs;
• eukaryote / protoctist, has many genes;
• many surface antigens / antigenic variation; A ref to mutation
• inside red blood cells / in liver cells / antigen concealment;
• difficult for immune system to operate / idea;
• dormant / in body for a long time / symptomless carriers / long incubation;
• different stages in life cycle in the body;
• resistance of, vector / mosquito, to insecticides; A mutation / selection
• mosquito, breeds in small areas of water; A implications
• breeds quickly;
• mosquitoes, spread over large area / widely distributed / fly a long way;
• mosquito control programmes disrupted by war etc;
• lack of infrastructure (for control programmes);
• problems with sleeping nets, described;
• more effective when soaked in insecticide;
• – no vaccine;
• people lose immunity if, malaria eradicated / move to non-endemic area;
• poor primary health care / few doctors or other medical personnel;
• ref to poor housing / slums / shanties;
• ref to remote rural areas;
• ref to cost of control programmes;
• ref to travel / migration;
• ref to change in climate;
• ref to education;
• ref to problems of biological control;
• AVP; e.g. effects of insectides on, ecosystems / humans
• AVP; side effects of drugs
• impossible to isolate infected people
• ref to sterilising male mosquitoes
• opening new areas of tropics
• different, species / strains, of malaria
• cost to individual
• ref to detection in bloodstream
• blood transfusions
• mother to fetus across placenta

 

Outline the problems associated with the elimination of malaria

• resistance of mosquitoes to insecticides;
• such as DDT/dieldrin;
• difficulty in controlling the breeding places;
• resistance of some strains of Plasmodium/no effective vaccine against Plasmodium;
• migration of both people (infected and uninfected);
• expensive;
• attitude of society to elimination programme by WHO;
• environmental effects of insecticides;

 

Explain the link between malaria and sickle cell anaemia prevalence.

• possession of sickle cell trait has selective advantage in malaria areas;
• pathogens does not survive in red blood cells
• do not suffer from malaria

 

Causes of sickle cell anaemia

• a faulty occurs on the haemoglobin molecule;
• the 6^th amino acid of the beta chain (146 amino acids)
• glutamic acid is replaced by valine;
• glutamic acid carries a negative charge and its polar, valine is non-polar;
• deoxygenated become less soluble;
• haemoglobin crystalizes into a rigid rod-shaped fibre;
• it is a result of a base in substitution;
• thymine of a DNA triplet code CTC is replaced by adenine to make a CAC;
• the affected gene is on chromosome 11;
• the faulty gene is codominant;
• effect expressed only in homozygous condition