Scientific Method – Case Study

How Malaria is Transmitted

1897 – Ronald Ross – English Physician

Observations:

- Doctors knew malaria was caused by microscopic parasite Plasmodium (Protist) because it was found in the blood of victims

-They did NOT know HOW the parasite was transmitted.

-Dr. Ross observed that patients in field hospitals without malaria were more likely to develop malaria in open wards than in wards with closed windows or screens

parasite Plasmodium falciparum

Hypothesis:

Ross proposed that mosquitos (Anopheles) in open wards might spread disease from patients with malaria to those without

(basis for further testing)

Sir Ronald Ross, Mrs. Ross, Mahomed Bux and laboratory assistants at the laboratory in Calcutta where the life history of the malaria parasite in birds was fully worked out in 1898.(Courtesy: London School of Hygiene and Tropical Medicine)

Predictions: Ross knew that if his hypothesis was correct, he could expect several consequences. Ross predicted that if Anopheles mosquitos were spreading malaria, then:

Mosquitoes that bit malaria patients and sucked up some of their blood, would have the living Plasmodium parasite in them. Parasites would be alive within the mosquitoes

Controlled Experiment:Control setup: mosquitoes feed on

blood from uninfected individuals (raised newly hatched mosquitoes and fed blood from uninfected person)

Experimental setup: mosquitoes feed on blood from malaria patients

Ross looked for living parasites in the mosquitoes – dissected each mosquito stomach

Results:Control group:

Experimental group:

Conclusions: Experiment confirmed hypothesis

Ross reconfirmed and extended his hypothesis with further experiments:

Ross suspected that parasites make their way from mosquito stomach to the salivary glands to be transferred to next person bit.

He waited longer than 1st experiment and careful dissection showed the parasites were present in the salivary glands

Common symptoms of malaria In the early stages, malaria symptoms are sometimes similar to those of many other infections caused by bacteria, viruses, or parasites. Symptoms may include:

Fever. Chills. Headache. Sweats. Fatigue. Nausea and vomiting.

Symptoms may appear in cycles and may come and go at different intensities and for different lengths of time. However, especially at the beginning of the illness, the symptoms may not follow this typical pattern.

The cyclic pattern of malaria symptoms is due to the life cycle of malaria parasites as they develop, reproduce, and are released from the red blood cells and liver cells in the human body. This cycle of symptoms is also one of the major indicators that you are infected with malaria.

Other common symptoms of malaria include:Dry (nonproductive) cough. Muscle and/or back pain. Enlarged spleen.

Rarely, malaria can lead to impaired function of the brain or spinal cord, seizures, or loss of consciousness.

Infection with the P. falciparum parasite is usually more serious and may become life-threatening.

Severe malariaDefinition of severe falciparum malaria13 A patient with severe falciparum malaria may present with confusion, or drowsiness with extreme weakness (prostration). In addition, the following may develop:cerebral malaria, defined as unrousable coma not attributable to any other cause in a patient with falciparum malaria generalized convulsions severe normocytic anaemia hypoglycaemia metabolic acidosis with respiratory distress fluid and electrolyte disturbances acute renal failure acute pulmonary oedema and adult respiratory distress syndrome (ARDS) circulatory collapse, shock, septicaemia (‘algid malaria’) abnormal bleeding jaundice haemoglobinuria high fever

Cerebral malaria is the most serious manifestation of severe falciparum malaria and is caused by the adherence of parasitised red blood cells to the walls of small blood vessels. In non-immune patients, cerebral malaria can develop rapidly from uncomplicated disease, and is associated with high parasitaemia. Cerebral malaria is characterised by bleeding, acute neurological symptoms, disturbance of consciousness, coma, and rapid death.