In this study session you will learn about two different methods used to identify malaria parasites in patients (parasite-based tests). But first you will need to make a clinical or ‘presumptive’ diagnosis of malaria, based on recognising the most common signs and symptoms of the disease, including severe malaria.
The most important malaria diagnostic method used at the community level is the rapid diagnostic test (RDT) for malaria. RDTs provide a quick way to tell whether a person with malaria-like symptoms actually has malaria, as the test takes only 15–20 minutes. The RDT detects certain chemicals in the blood that are produced by malaria parasites if they are present. In this study session you will learn how to use the RDT kit for malaria, including the precautions you must take when performing an RDT, and how to interpret the results.
Finally, we will briefly describe how malaria can be diagnosed using microscopic techniques to detect the presence of parasites in blood smears. You are not expected to use a microscope for diagnosis, but it is useful for you to know what is involved in microscopic diagnosis, which is done at health centres and hospitals.
When you have studied this session, you should be able to:
7.1 Define and use correctly all of the key words printed in bold. (SAQ 7.1)
7.2 Describe how to diagnose malaria and assess the severity of cases, based on clinical signs and symptoms. (SAQs 7.2 and 7.3)
7.3 List the advantages and limitations of rapid diagnostic tests (RDTs) for malaria. (SAQ 7.4)
7.4 Explain how to perform RDTs for malaria safely and effectively, and record the results accurately. (SAQs 7.5 and 7.6)
7.5 Explain how microscopic examination is used to diagnose malaria and state its advantages over RDTs. (SAQ 7.7)
In Study Session 2, you learned how to classify and diagnose communicable diseases according to their clinical symptoms. In this section, you will be able to apply those principles to the clinical diagnosis of malaria. In Study Session 5 you learned that some members of the population, such as children under the age of five years and pregnant women, are at a higher risk of getting malaria due to their weaker immunity. By learning how to identify malaria with clinical diagnosis (and confirm it with RDTs) you will be able to provide effective and prompt treatment of malaria to patients at the community level. By identifying signs and symptoms of severe malaria, you will also be able to refer patients that need higher medical care to the health centre or hospital. In this way your knowledge and actions could save many lives, as poorly diagnosed and managed malaria could kill many people in your community.
The clinical symptoms of malaria vary from very mild to very severe, depending on several factors. In areas where malaria is very common, adults with the disease may show just a slight increase in body temperature. However, pregnant women, and in particular, young children, often have a severe illness with many symptoms. The most important symptom of malaria is fever (or a history of fever within the last two to three days). An attack often begins with shivering (body shaking). This is followed by a period of fever, and finally there is profuse sweating. During an attack the patient often complains of headache and pains in the back, joints, and all over the body (Figure 7.1).
There may also be loss of appetite, vomiting, and diarrhoea. The patient may feel better the next day, but may have another attack the day after that, and so on. If untreated (or inadequately treated), malaria can cause several weeks or months of poor health because of repeated attacks of fever, anaemia (see Box 7.1) and general weakness. Some patients rapidly become very ill and may die within a few days.
Anaemia means not enough haemoglobin in the blood. Haemoglobin is the red substance in the red blood cells which carries oxygen. Malaria parasites destroy the red blood cells and so malaria may cause anaemia. Anaemia may also have other causes (for example, not enough iron in the food). You can recognise anaemia by looking at the patient’s hands: the palms of a person with anaemia do not have the redness of a healthy person’s palms. If the red colour of the inner eyelid or mouth is paler than in a healthy person, the patient has anaemia. Breathlessness and a fast pulse may also be present, because the person’s blood cannot carry enough oxygen for their needs.
A critical feature that may help you to recognise if a fever is due to malaria or not is that malarial fever occurs in cycles – periods of fever alternate with periods in which the patient shows normal body temperature (below 37.5°C) and no symptoms. The stages of malarial fever attacks are shown in Table 7.1. (You will learn more about how to identify malaria cases in Section 7.2.3).
|Stage of malarial fever attack|
|Stage name||Cold stage||Hot stage||Sweating stage|
Main clinical symptoms
|How long symptoms last||15–60 minutes||2–6 hours||2–4 hours|
A four-year-old patient is presented to you with fever of 38°C. The child also has poor appetite, is weak and has yellowish eyes. What other questions should you ask his mother or guardian to try and find out if the child is suffering from malaria? Give reasons for your answer.
You should try to find out how long the child has had fever. You should also find out whether the fever has alternated with a stage of sweating, followed by a cold, shivering stage. A child with a fever could have malaria, but fever can also be a symptom of other diseases. However, a child who has gone through stages of fever, sweating and shivering is much more likely to be suffering from malaria, as this is the typical pattern of malarial fever attacks.
Malarial fever attacks usually repeat every 48 hours, for patients infected with the two most common species of plasmodium in Ethiopia, P. vivax and P. falciparum.
Symptoms of malaria usually start to appear 7 to 21 days after the bite of an infected mosquito. However, the normal incubation period is different for different species of Plasmodium, as described in Study Session 5. Remember that the incubation period is the time between the parasite getting into the blood of a person and the onset of symptoms.
Can you recall, from what you learned in Study Session 5, which of the following malaria parasites has the shortest incubation period? Which has the longest?
P. falciparum has the shortest and P. malariae has the longest incubation period.
A patient who is not treated may develop severe complications and may die, or may continue to have cycles of fever alternating with symptom-free periods. In general, the more Plasmodium parasites there are in the blood, the more severe the disease will be.
Disease progression varies according to the species of Plasmodium that has infected the patient. Patients infected with P. vivax, especially for the first time, can be quite ill. However, P. vivax rarely causes complications or results in death. Relapses (return of malaria symptoms due to activation of an old infection) due to P. vivax can occur for several years.
Patients with serious complications are generally referred to a health centre; you will learn how to refer such patients in Study Session 8.
By contrast, P. falciparum is the most lethal form of malaria infection. It causes the most serious complications, which are anaemia (Box 7.1 above) and cerebral malaria. In cerebral malaria, red blood cells infected by the parasite stick to small blood vessels in the brain. This reduces the flow of blood and the supply of oxygen and nutrients to the brain. If untreated, cerebral malaria can kill the patient in 24–48 hours. It most commonly affects young children (Figure 7.2).
The most important element in the clinical diagnosis of malaria is for you to be alert and to suspect malaria in all patients with fever, whether your catchment area is located in a malarious area or not. Because the distribution of malaria in Ethiopia is patchy, it is also very important for you to find out the geographical and travel history of a patient who shows signs and symptoms of malaria, most importantly fever.
In non-malarious areas, you should suspect malaria in a patient who has high fever, or has had fever in the last 48 hours, if the person has travelled to a malarious area or country in the previous two weeks. In malarious areas, fever, or a history of fever in the last 48 hours, should be enough for you to suspect malaria in a patient. You should pay particular attention to children under the age of five years and pregnant mothers, as these groups are at a higher risk than others.
Why do you think children are at higher risk of getting severely ill or dying of malaria than adults?
Children have a much weaker immunity against malaria. Immunity develops after repeated exposures to the malaria parasite and this takes time.
You can recognise malaria by asking the right questions and looking for the important signs (see Box 7.2):
If the patient has had fever during the past 2–3 days, first ask about and then look for danger signs:
If the answer to any of these questions is yes, the patient has severe malaria. The patient’s life is in danger. Urgent treatment is needed to save the patient’s life so refer immediately to the nearest health centre.
If you suspect that a patient may have malaria, you will need to confirm the clinical diagnosis using specific tests to identify the presence of the malaria parasite or its products in the blood. This process is called parasitological or parasite-based diagnosis. In areas with a risk of malaria, or in patients who have travelled back from malaria-endemic areas, fever should be enough to make you suspect malaria and do a confirmatory test. The parasitological diagnosis of malaria can be divided into microscopic and non-microscopic tests. Microscopic tests involve the use of a microscope to see the parasite in the blood of a patient. At health post level you will not be able to carry out microscope tests, but they will be discussed briefly in Section 7.2.3. First we describe the non-microscopic tests, also known as rapid diagnostic tests (RDTs).
The national malaria diagnosis policy in Ethiopia is that Health Extension Workers and Practitioners must test anyone suspected of having malaria by using the RDT for malaria. RDTs are now available in all health posts in areas where malaria is a risk and you will receive some practical training in how to use them.
The Ethiopian national guidelines state that malaria treatment at health post level, or referral from the health post to the health centre, should be based on RDT test results, so knowing how to use the RDT properly is a very important part of your job. In this section you will learn how to use the RDTs more effectively. You will also learn about the precautions you have to take to protect yourself and other patients when working with blood.
RDTs test whether a person with malaria-like symptoms actually has malaria by testing the blood of the patient for chemical substances produced by malaria parasites. Malaria parasites produce proteins called antigens. RDTs detect malaria antigens, so if they are present, the person will test positive. If malaria antigens are not present, the person will test negative.
RDTs enable you to find out if a fever is really caused by malaria rather than by other illnesses. You can also get information about which malaria parasites may be causing the infection. The information provided by RDTs is important for three main reasons:
Can you remember which malaria parasite causes the most serious malaria in Ethiopia?
P. falciparum can kill a person in 24–48 hours, for example by causing cerebral malaria. P. vivax is less likely to cause complications and is rarely fatal.
You will learn about malaria case management with these drugs in Study Session 8.
By using the RDT you will be able to test for malaria parasites in a patient’s blood, and in this way to provide a more accurate diagnosis than a clinical or presumptive diagnosis. RDTs give results in about 15–20 minutes, so a patient with malaria can begin treatment right away. RDTs do not require any expensive or complicated equipment and can be used by you in the patient’s home. You should be able to learn to use RDTs in just a few hours in your practical training programme.
RDTs are very effective for diagnosing malaria, but there are some things they cannot do.
First, RDTs cannot test how many malaria parasites there are in the blood – they can only test whether parasites are present or absent. In fact, RDTs do not detect actual parasites; they detect parasite antigens, as mentioned above. Some parasite antigens can remain in the blood for at least two weeks after the parasites have been killed by drugs.
What will be the result if an RDT is used on a person within two weeks of taking anti-malarial drugs, and should you trust the result? Explain your answer.
An RDT used within two weeks of drug treatment may still detect parasite antigens and so give a positive result for malaria infection, even if the person no longer has parasites, because the parasites have been killed by the drugs. This is why this positive result cannot be trusted.
Second, RDTs can be damaged by heat and humidity, so the RDT should not be removed from its sealed package before you are ready to use it. If a package has been open for some time before the RDT is used, the RDT may be damaged and can give an invalid (false) result. You should discard this package and use another, unopened, package.
The national malaria treatment guidelines now recommend the use of parasite-based diagnosis using RDTs for malaria by community health workers for all age groups, except when the RDT is not available due to logistics problems.
We now explain how to use an RDT, and how to interpret the results.
Here is the checklist that you must follow when you are using an RDT for malaria diagnosis.
(i) Check the expiry date on the package. Do not use RDTs that have expired.
(ii) Put on gloves before beginning (Figure 7.3). Use a new pair of gloves for each patient. Do not re-use gloves.
Figures 7.3 to 7.10 are from WHO, 2006, How to Use a Malaria Rapid Diagnostic Test (RDT): A Guide for Training CHWs and Other Health Workers.
(iii) Open the RDT package and remove the contents. The blood-transfer device — it could be a capillary tube, straw, loop, pipette or other device — is used to collect blood and transfer it to the test cassette. (Once the packet is opened, the ‘desiccant’ sachet which absorbs moisture from the atmosphere in the package should be discarded.) The test cassette (shown later, in Figure 7.8) is used to conduct the test. The square hole labeled ‘A’ is where you add the blood. The round hole labeled ‘B’ is where you add the buffer.
(iv) Write the patient’s name on the cassette (Figure 7.4).
(v) Open the alcohol swab and clean the patient’s third or fourth finger with alcohol (Figure 7.5). This is to prevent infection. Other fingers may be used if necessary. Ask the patient: ‘Are you right-handed or left-handed?’ If the patient is right-handed, choose a finger on their left hand. If the patient is left-handed, choose a finger on their right hand.
(vi) After cleaning the finger with the alcohol swab, the finger must be allowed to air dry. After using the alcohol swab, place it on its wrapper and set it aside on the table. You will use it again to stop the bleeding after you collect the patient’s blood.
(vii) Once the patient’s finger is dry, open the lancet. Prick the patient’s finger, preferably towards the side of the pulp (ball) of the finger. Discard the lancet in a sharps-only container immediately after using it (Figure 7.6).
Never put the lancet down before discarding it. Never discard the lancet in a non-sharps container. Never use a lancet on more than one person.
(viii) Turn the ‘patient’s’ arm so their palm is facing downward. Squeeze the pricked finger and allow a drop to well up below the finger tip as in Figure 7.7. Use the loop or capillary tube or straw or the pipette to collect the drop from underneath. Once you have collected a sufficient amount of blood, you may hand the alcohol swab back to the patient and show him or her how to use it to stop the bleeding.
(ix) Use the device (capillary tube, straw, loop, pipette or other) to add the drop of blood to the sample window (square hole labeled with the letter A, see Figure 7.8). The blood needs to reach and be absorbed by the pad at the base of the square hole. If the blood is mostly deposited on the plastic edges of the well, but does not reach the pad, the test will not work correctly. Deposit the blood in the correct place using the capillary tube, straw, loop, pipette or other. Adding too much or too little blood can cause the test to give an invalid result or be difficult to read.
(x) Add the buffer solution to the round hole labeled B. Hold the bottle vertically when adding the buffer solution, as in Figure 7.9. This ensures the correct drop size.
(xi) Wait for the correct duration of time (15 or 20 minutes) after adding buffer before reading the test results.
(xii) Discard the blood-collection device (e.g. capillary tube) safely after use.
(xiii) Remove and discard your gloves at this time. To avoid possible contamination, the used gloves should be discarded in the non-sharps container before you do anything else.
The different possible results and what they mean are illustrated in Figure 7.10 and summarised in Table 7.2.
Table 7.2 Malaria RDT interpretation chart.
As you can see from Figure 7.10 and Table 7.2, sometimes the result can be invalid, that is, it could be incorrect.
What should you do if the test result is invalid?
Discard the RDT cassette. Open a new cassette and repeat the test using the new cassette.
Microscopic diagnosis of malaria is done by a trained laboratory technician at health centre or hospital level. It is not your responsibility to do a microscope test, but this section will briefly explain it so you understand the technique.
Microscopic diagnosis involves taking a small amount of blood from the patient, staining it and looking at it under a microscope to check for malaria parasites. In most cases of malaria, microscopic examination of thick and thin films of finger-prick blood will reveal malaria parasites. Thick films are 20–40 times more sensitive than thin films for detecting Plasmodium parasites, and are particularly useful if the number of parasites is low. Thin smears are also useful as they can allow identification of particular Plasmodium species (Figure 7.11). The diagnostic accuracy relies on the quality of the blood smear and the experience of laboratory personnel.
In Study Session 7, you have learned that:
Now that you have completed this study session, you can assess how well you have achieved its Learning Outcomes by answering these questions. Write your answers in your Study Diary and discuss them with your Tutor at the next Study Support Meeting. You can check your answers with the Notes on the Self-Assessment Questions at the end of this Module.
What method is available to you at health post level to allow you to make a parasite-based diagnosis of malaria?
The RDT or Rapid Diagnostic Test for malaria is available at health post level.
Malaria is rare in your village. However, a 25 year-old male comes to your health post complaining of loss of appetite and muscle aches. You suspect malaria, but you don’t have an RDT kit to confirm your diagnosis. What questions should you ask him to either exclude malaria as a possible diagnosis, or decide that you should treat him for malaria?
You would ask him about his travel history to malaria-endemic areas in the last two weeks. You would also ask him if he has had fever in the last two to three days.
A five-year-old child comes to your health post with fever. He was tested with an RDT and the result was positive for falciparum malaria. Before treating and sending him home, you have to check for signs of severe malaria in case he needs a referral. What are the signs and symptoms you would look for?
The danger signs of severe malaria are anaemia, convulsions, repeated vomiting, high fever (>39˚C), shivering, sweating, severe dehydration, drowsiness or confusion, and reduced urine output.
You have learned that RDT and microscopy are two simple and useful methods to diagnose malaria. List two important advantages of RDT over microscopy.
You are confronted with more than 20 fever cases in the community around your health post at the same time. You will test all patients with RDTs for malaria. What do you do to avoid any mix-up of results?
Write each patient’s name on the RDT cassette to avoid mixing-up the results if you have to do several tests at the same time.
List the precautions you need to take to avoid contaminating yourself and your patients with another person’s blood, when performing an RDT for malaria.
You treated the five-year-old child positive for falciparum malaria in SAQ 7.3, according to the national guideline. The child comes back after three days with fever and you again test him with an RDT. The patient was again positive for falciparum malaria.