Define Disease

- The term disease denotes any condition or disorder that disrupts the steady state of well being of the body.
- Health is a state of physical, mental and emotional well being in the internal environment of the body.
- Some of the causes of diseases are due to entry of pathogens and parasites.
- Pathogens include bacteria, viruses, protozoa and fungi.
- Parasites are organisms which live on or in the body of another organisms.
- Vectors are animals that carry the pathogen from are person to another.
- Most are ectoparasites that transmit the disease as they feed.

Bacterial Diseases in Humans

Cholera

- Causative agent is a bacterium called Vibrio cholerae.
- It is spread through water and food contaminated by human faeces containing the bacteria.
- The bacteria produce a powerful toxin, enterotoxin, that causes inflammation of the wall of the intestine leading to:

Signs and Symptoms of Cholera

• Severe diarrhoea that leads to excessive water loss from body.
• Abdominal pain
• Vomiting
• Dehydration which may lead to death.

Prevention and Control of Cholera

- Adequate sanitation such as water purification sewage treatment and proper disposal of human faeces.
- Public and personal hygiene e.g washing hands before meals and washing fruits and vegetables, boiling drinking water.
- Carriers should be identified, isolated and treated during outbreaks.

Treatment of Cholera

- Use of appropriate antibiotics.
- Correcting fluid loss by injecting fluids or by administration of oral rehydration solutions.

Typhoid

Causative agent of Typhoid

- The disease is caused by Salmonella typhi.
- Transmission is through contaminated water and food.
- It is also transmitted by certain 'e.g foods, e.g. oysters, mussels and shell fish.

Symptoms of Typhoid

• Fever
• Muscle pains
• Headache
• Spots on the trunk of the body
• Diarrhoea
• In severe cases mental confusion may result and death.

Prevention of Typhoid

• Boil drinking water.
• Proper sewage treatment.
• Proper disposal of faeces, if not flushed use deep pit latrines.
• Observe personal hygiene e.g. washing hands before meals.
• Washing fruits and vegetables.

Treatment of Typhoid

- Use of appropriate antibiotics.

Protozoan Diseases in Humans

Malaria

- Malaria is caused by the protozoan plasmodium.
- The most common species of plasmodium are P. falciparum, P. vivax, P. rnalariae and P. ovale with varying degree of severity.

Transmission of Malaria

- Is by female anopheles mosquito as it gets a blood meal.

Symptoms of Malaria

- Headache, sweating, shivering, high temperature (40-41 0C) chills and joint pains.
- The abdomen becomes tender due to destruction of red blood cells by the parasites.

Prevention of Malaria

- Destroy breeding grounds for mosquitoes by clearing bushes and draining stagnant water.
- Kill mosquito larvae by spraying water surfaces with oil.
- Use insecticides to kill adult mosquitoes.
- Sleeping under a mosquito net.
- Take preventive drugs.

Treatment of Malaria

- Use appropriate anti-malarial drugs.

Amoebic Dysentery (Amoebiasis)

Cause of Amoebic Dysentery

- This disease is caused by Entamoeba histolytica.
- The parasites live in the intestinal tract but may occasionally spread to the liver.
- Transmission - They are transmitted through contaminated water and food especially salads.

Symptoms of Amoebic Dysentery

- Abdominal pain, nausea and diarrhoea.
- The parasites cause ulceration of the intestinal tract, which results in diarrhoea.

Prevention and Control of Amoebic Dysentery

- Proper disposal of human faeces.
- Boiling water before drinking.
- Personal hygiene e.g. washing hands before meals.
- Washing vegetables and steaming particularly salads and fruits before eating.

Treatment of Amoebic Dysentery

- Treatment of infected people with appropriate drugs.

Parasitic Diseases in Humans

Ascariasis

- It is caused by Ascaris lumbricoides.
- Ascaris lumbricoides is a large parasitic worm that lives in the intestines of a man or pig, feeding on the digested food of the host.
- The body of the worm is tapered at both ends.
- The female is longer than the male.

Transmission of Ascariasis

- The host eats food contaminated with the eggs, the embryo worms hatch out in the intestine.
- The embryo worms then bore into the blood vessels of the intestine.
- They are carried in the bloodstream to the heart and then into the lungs.
- As they travel through the bloodstream, they grow in size.
- After sometime, the worms are coughed out from the air passages and into the oesophagus.
- They are then swallowed, eventually finding their way into the intestines where they grow into mature worms.

Effects of Ascaris lumbricoides on the Host

- The parasites feed on the host's digested food.
- This results in malnutrition especially in children.
- If the worms are too many, they may block the intestine and interfere with digestion.
- The worms sometimes wander along the alimentary canal and may pass through the nose or mouth.
- In this way, they interfere with breathing and may cause serious illness.
- The larvae may cause severe internal bleeding as they penetrate the wall of the intestine.

Adaptive Characteristics of Ascaris lumbricoides

- The female lays as many as 25 million eggs.
- This ensures the continuation of the species.
- Eggs are covered by a protective cuticle that prevents them from dehydration.
- The adult worms tolerate low oxygen concentration.
- Have mouth parts for sucking food and other fluids in the intestines.
- Has a thick cuticle or pellicle to protect it from digestive enzymes produced by the host.

Control and Prevention of Ascariasis

- Personal hygiene e.g. washing hands before eating.
- Proper disposal of faeces.
- Washing of fruits and vegetables.

Treatment of Ascariasis

- Deworm using appropriate drugs anthelmintics.

Schistosoma

- Schistosoma or bilharzia worm is a flat worm, parasitic on human beings and fresh water snails. (Biomphalaria and Bulinus.)
- The snail act as intermediate host.

Transmission of Schistosoma

• Schistosomiasis also known as a bilharsiasis is caused by several species of the genus schistosoma.
• Schistosoma haematobium infects the urinary system mainly the bladder.
• S. japonicum and S. mansoni both infect the intestines.
• Schistosoma haemotobium is common in East Africa where irrigation is practised and where slow moving fresh water streams harbour snails.
• It is spread through contamination of water by faeces and urine from infected persons.
• The embryo (miracidium) that hatch in water penetrates into snails of the species Biompharahia and Bulinus.
• Inside the snail's body, the miracidium undergoes development and multiple fission to produce rediae.
• The rediae are released into the water and develop to form cercariae which infect human through:
  • Drinking the water
  • Wading in water;
  • Bathing in snail-infested water.
• The cercaria burrows through the skin and enters blood vessel.

Effects of Schistosoma on the Host

- Inflammation of tissues where egg lodge.
- Ulceration where eggs calcify.
- Egg block small arteries in lungs leading to less aeration of blood.
- The body turns blue - a condition known as cyanosis.
- If eggs lodge in heart or brain, lesions formed can lead to death.
- Bleeding occurs as the worms burrow into blood vessels (faeces or urine has blood).
- Pain and difficulty in passing out urine.
- Nausea and vomiting.
- When eggs lodge in liver ulceration results in liver cirrhosis.
- Death eventually occurs.

Adaptive Characteristics of Schistosoma

• The female has a thin body and fits into small blood vessels to lay eggs.
• Eggs are able to burrow out of blood vessel into intestine lumen.
• Many eggs are laid to ensure the survival of the parasite.
• Large numbers of cercariae are released by snail.
• The miracidia and cercariae larvae have glands that secrete lytic enzymes which soften the tissue to allow for penetration into host.
• The male has a gynecophoric canal that carries the female to ensure that eggs are fertilised before being shed.
• Has suckers for attachment.

Prevention and Control of Bilharzia

• Drain all stagnant water.
• Boil drinking water.
• Do not wade bare feet in water.
• Wear long rubber boots and gloves (for those who work in rice fields).
• Eliminate snails, by spraying with molluscides.
• Reporting to doctor early when symptoms appear for early treatment.