Semi-immunes are either not sick at all and run around playing football all day with chronic mild malaria, or get a mild attack every few months if they are either bitten more than usual or have another condition which pushes down their immunity, such as an infection or pregnancy. So malaria is a potentially fatal disease to expatriates, visitors, pregnant women and very young children. However, by the age of 5, someone who has lived in a malaria area all their life and been bitten by infected mosquitoes continually is
semi-immune. For them malaria is either a mild easily-treated disease or a self-limiting hardly noticed nuisance.

So how to diagnose malaria?
Recently we have seen far more malaria than usual, with many people talking about “new types” and “cerebral malaria” and how treatment doesn’t work. All complete nonsense, of course, but anyone who has been here 6 months thinks they are an expert in anything medical and malaria in particular. So that is the first thing to know about diagnosis. Where were you 8 to 10 days ago? If the answer is “lake side” then that is a big risk factor for malaria. If the answer is “India” or “Europe” then malaria is almost impossible. After being bitten by an infected mosquito, the parasites go into the liver. Most of them come out 5 and a half to 6 days later. The first wave of parasites
cannot mature and release the fever toxins until they are 2 days old so the first fever of malaria cannot come in less than 8 days. Most people will get their first severe symptoms 10 days after being bitten. I have often had patients who have been told they had malaria after being in the country only 4 or 5 days. That is impossible. The diagnosis has to be wrong. Is it ever possible? Well yes. In a semi-immune the disease could grumble on for a month or two, so it is possible to see malaria in a Malawian returning from a short trip abroad. “Plasmodium malariae” has been known to relapse 20 years after leaving a malaria area. So all these unlikely scenarios could mean that someone has visible parasites in the blood 6 days after arrival. But if you are new, never been to an endemic area before, and have been here less than 8 days, it cannot be malaria.

So that is the first point in diagnosis: where were you 10 days ago? Secondly, are you taking prophylaxis?
Almost all people with malaria that we see are taking nothing. I have not heard of a single reliable report of malaria in someone taking mephloquin or Malarone properly, and I have only ever seen 3 cases in someone taking doxycycline. I have had many patients who have been told they have malaria when they have been taking a good prophylactic. I doubt the diagnosis in almost all of them! I can remember one group of gap year volunteers who were all on mephloquin and all had acute diarrhoea with fever and vomiting after eating the same meal, so obviously an acute attack of gastroenteritis. They all went to the same doctor and were all given Halfan for “malaria”. Halfan and mephloquin is a well-known potentially fatal combination, and these students were lucky they all survived. Many people are given artemether drugs for “malaria” and, when they do not get better, are told artemether drugs do not work and given a quinine drip. They then get better because many diseases get better in 5 to 6 days anyway. Does it matter? Yes! I know many travellers who have stopped taking their prophylaxis because they kept getting “malaria”, thinking the prophylaxis didn’t work. This is dangerous and in travellers a possibly fatal mistake. These drugs do work! In most cases, perhaps all, it is the diagnosis that is wrong. So that is the next question about diagnosis: are you taking a prophylactic? If you are taking a recommended one, i.e. mephloquin, Malarone, primaquin or doxycycline, then it is possible but very unlikely you have malaria.

Next, what are the symptoms?
Someone with malaria can have any symptom, I agree. They can even have a rash, in-growing toenails or haemorrhoids. But malaria is not the only disease that makes you sick! Most people with a cough, a runny nose, or a sore throat or pus on their tonsils have a respiratory infection. Of course, someone with a cold may also have malaria but it is not very likely. Add up all the unlikelies, e.g. symptoms don’t fit, you’re taking mephloquin, you only left Malawi 7 days ago and really, what are the chances you have malaria? Most people with acute diarrhoea, fever and vomiting have an acute gastroenteritis, probably shigella or salmonella. This is in our experience by far is the commonest cause of a high fever in a visitor. Yes, someone with acute gastroenteritis may have malaria but, add up all the unlikeliest, and once again it is incredible how many people accept the diagnosis without question. These acute gastro’s can go on for a long time, which is why we hear the story “artemether doesn’t work”. A very dangerous untruth. Are there any specific symptoms or signs of malaria? No, not really. Most people with malaria will have sudden onset of fever, headache and joint pains, without much else. After 2 days the symptoms get very much worse, often with a sudden rigor, vomiting, high fever, headache and aching all over. An untold number of diseases can do this: dengue and a dozen other similar viruses, flu, Ebola, leptospirosis, all the different ricketsias, borellia, the list is quiete literally endless! There are NO specific signs or symptoms of malaria; hundreds of other diseases can be mistaken for malaria. This is why it is so dangerous to assume that every fever is malaria! We have seen TB meningitis treated as cerebral malaria for 3 days and the patient nearly died; also ordinary meningitis diagnosed as malaria, some have died. Pneumonia, a bleeding peptic ulcer, hepatitis, septiceamia, all have been diagnosed as malaria, when the patients didn’t get better (medivac’d as having “resistant malaria”), all potentially fatal diseases where the diagnosis was delayed because of the wrong diagnosis of malaria. So, YES
it is important! So where have you been, are you taking prophylaxis, and do the symptoms fit? All these play a role in diagnosis.

So how do you make the right diagnosis?
The official correct answer is a thick blood film, looked at by an expert and if negative, repeated after 24 hours. The “gold standard” is two independent experts agreeing on a blood slide. That is how we measure the success of other methods.

Sounds easy. What about reality? First of all, missing it. In the UK about 20 people die out of about 2,000 cases every year, almost all because of late diagnosis. Missing it in the first day or two is inevitable; you just cannot possibly find malaria in every early case as the parasites simply are not visible in the peripheral blood. If there are not enough to be seen in the blood slide, then there are not enough to cause trouble. The next day there may be the same number but bigger and easier to see, or there may be 10 times as many. Still not
anywhere near enough to cause trouble. So, if the very early malaria is missed, it doesn’t matter and you can find them without any danger the next day. Vivax is particularly difficult to find and you can miss them for a week and it still doesn’t matter, as it is never dangerous. So a good lesson: missing malaria is honest, normal, inevitable and if repeated the next day, is not dangerous. “Don’t treat it until you find it and keep looking until you do” is a good maxim to live by.

What about the other way, finding malaria where none exists?
This is very easy! The gold standard is an expert with a good microscope and a new slide with clean stains. Reality is quite different. A busy microscopist in a hurry, a scratched slide reused 20 times, stains that should have been changed hours ago and are now growing bacteria which look like parasites, with a microscope that hasn’t been cleaned for a week! Add to that thinking squashed platelets are parasites, and it is no wonder that all over the world finding malaria when none exist is extremely common. One research I read was in UN soldiers in Angola where, if I remember correctly, about 1,600
had been diagnosed with malaria over a 2-year period, and antibody tests showed that only 3 had ever had malaria. The diagnosis was wrong in 99.8% of cases!!

So what can the poor sick traveller do?
In the next Eye we will look at the self-test kits and come to a common sense answer.