Learning Outcomes:
Diseases caused by these major pathogen groups include:
- tuberculosis, tetanus, crown gall of plants
- chytridiomycosis (amphibian chytrid fungus disease)
- malaria, Phytophthora dieback (jarrah dieback is now considered a Protist)
- influenza, Ross River virus, viral diseases of honeybees, Australian bat lyssavirus (SU)
Malaria (pp.446-447)
What is it?
12 . After 10-18 days, the parasites are “sporozoites” again in the mosquito’s saliva
- Malaria is a mosquito-borne infectious disease affecting humans and other animals
- It is caused by the protozoan parasite Plasmodium.
- Human malaria is caused by four different species of Plasmodium
- P. falciparum
- P. malariae
- P. ovale
- P. vivax
- Malaria, is alone responsible for 6.4% of infectious disease mortality.
- Nearly half of the world's population is at risk of malaria.
- In 2016, malaria caused an estimated 216 million clinical episodes, and 445,000 deaths
- Increased prevention and control measures have led to a 29% reduction in malaria mortality rates globally since 2010.
- Mosquito vectors prefer warm and wet conditions - thus climatic changes, tsunamis, tropical cyclones, or any other cause for a more wet and warm environment can result in a Malaria outbreak.
- The life cycle involves the infection of two hosts:
- a human
- the female anopheles mosquito.
- A mosquito vector takes a blood meal and injects Plasmodium "sporocytes"
- In humans, the parasites grow and multiply first in the liver cells
- Sporocytes mature into schizonts.
- The Schizonts rupture and release merozites
- Merozites infect red blood cells (RBC).
- In the blood, successive broods of parasites grow inside RBC this releases daughter parasites “merozoites”, that continue the cycle by invading other RBC.
- Some merozites mature into "gametocytes" cause the symptoms of malaria. Gametocytes are picked up by a female Anopheles mosquito during a blood meal.
12 . After 10-18 days, the parasites are “sporozoites” again in the mosquito’s saliva
Modes of transmission:
Drugs
- Mosquito-Borne Malaria (most common).
- Congenital Malaria: infected mothers transmit parasites to their child during pregnancy before or during delivery.
- Blood Transfusion-Transmitted Malaria: a rare but severe complication in blood recipients.
- The incubation period in most cases varies from 7 to 30 days
- The classical (but rarely observed) malaria attack lasts 6–10 hours.
- Malaria attacks take place every 2 to 3 days.
- Symptoms of Malaria attacks consists of
- A cold stage (sensation of cold, shivering)
- A hot stage (fever, headaches, vomiting; seizures in young children)
- A sweating stage (sweats, return to normal temperature, tiredness)
- Elevated temperatures
- Perspiration
- Weakness
- Enlarged spleen
- Mild jaundice
- Enlargement of the liver
- Increased respiratory rate
- Cerebral malaria: abnormal behavior, impairment of consciousness, seizures, coma
- Severe anemia due to hemolysis
- Hemoglobinuria (hemoglobin in the urine) due to hemolysis
- Acute respiratory distress syndrome in the lungs that inhibits oxygen exchange
- Abnormalities in blood coagulation
- Low blood pressure caused by cardiovascular collapse
- Acute kidney injury
- Hyperparasitemia, where more than 5% of the red blood cells are infected by malaria parasites
- Metabolic acidosis (excessive acidity in the blood and tissue fluids)
- Hypoglycemia (low blood glucose)
- Drugs that kill the parasite are used, called antimalarials.
- If you contract malaria while taking one type of antimalarial drug, the same drug cannot be used to treat the infection due to resistance.
- Different drugs target different features of the parasite’s biology and life cycle.
- Thus, drugs are combined to make sure the malaria parasite is removed from all areas of the body.
- Combinations of drugs are also used to try to prevent the parasite from developing resistance to an individual drug.
- If any parasites are left in the body after treatment, the disease may return months or even years later.
- Partial immunity can be developed over years of exposure to the disease reducing the severity.
- Most malaria deaths occur in young children under five years whose bodies developed any immunity to the parasite.
Drugs
- Antimalarial drugs can also be used to prevent malaria. This is known as chemoprophylaxis.
- Mosquirix for use against Plasmodium falciparum malaria in Africa.
- The vaccine works by preventing the malaria parasite from entering the liver
- A booster dose was found to be crucial as the effectiveness of the vaccine reduced over time.
- The vaccine is a ‘magic bullet’ against malaria but a step towards the development of future malaria vaccines.
- Indoor residual spraying involves spraying insecticide once or twice a year on all indoor surfaces
- Long-lasting insecticidal nets are mosquito nets that are also sprayed with an insecticide. The nets also result in large-scale killing of mosquitoes when used by entire communities.
- Larviciding involves treating the breeding sites of the mosquito with substances that kill the larval stages of the insect. It is effective, but only in areas where mosquito breeding sites are fixed in one place and easy to find.
Jarrah Dieback (Phytophthora) (pp. 448-450)
What is it?
https://medium.com/@grdninfoonline/phytophthora-root-rot-symptoms-treatment-prevention-8755d34e4a1c
https://www.dpaw.wa.gov.au/management/pests-diseases/129-phytophthora-dieback
- Phytophthora dieback is caused by the plant pathogen, Phytophthora cinnamomi.
- NOTE: Phytophthora was orginally believed to be a fungus but is now believed to be a protist - some information sources may still refer to it as a fungus.
- It lives in the roots of plants
- It kills susceptible plants, such as banksias, jarrah and grass trees, by attacking their root systems.
- Dieback is the symptom of a Phytophthora infection
- It affects more than 40 per cent of the native plant species and half of the endangered ones in the south-west of Western Australia.
- The plants die because they cannot take up the water and nutrients they need.
- It's is not easy to detect as infected plants often appear to be dying from drought.
- Phytophthora disease also affects many agricultural crops and garden plants.
- The protist is spread through the movement of soil (indirect transmission) and mud, typically by vehicles and footwear.
- Thrives in soils in wet and warm conditions (15 to 30 degrees celcius)
- It also moves in free water and via root-to root contact (direct trnasmission) between plants.
- Often spreads down slopes with the flow of water in the soil
- If infected plants are planted in an uninfected area this will introduce the disease to the new area.
- There is no known cure for the disease.
- Remove infected plants
- Improve Soil Drainage (Phytophthora thrives in moist soils)
- Soil Testing and plant care The healthier your plants and trees are, the less susceptible to infections.
- Hydrogen Peroxide application to the soil is effective in killing pathogens and diseases like Phytophthora in a small area.
- No Composting or Mulching of infected specimens
- Plant Disease Resistant Species in areas that in the past have been affected by Phytophthora
- Control Weed Growth (weeds are renowned for harboring pathogens)
- Equipment Care (pruning, cutting, and digging equipment must always be cleaned after use).
- Planning around wet and muddy conditions. Avoiding entering areas when conditions are particularly muddy.
- Shoe and vehicle wash-down stations
- Boardwalks to keep people up off of the soil.
- Parking facilities to prevent vehicles parking randomly on soil in bush areas
- Closure of infected areas to public during warm wet periods
- Public education so that people are able to take responsibility for cleanliness
- Controlling water flow from infected to uninfected areas.
https://medium.com/@grdninfoonline/phytophthora-root-rot-symptoms-treatment-prevention-8755d34e4a1c
https://www.dpaw.wa.gov.au/management/pests-diseases/129-phytophthora-dieback