Malaria

Notification requirement for malaria

Malaria is a ‘routine’ notifiable condition and must be notified by medical practitioners and pathology services in writing within 5 days of diagnosis.

This is a Victorian statutory requirement.

Primary school and children’s services centres exclusion for malaria

Exclusion is not required.

Infectious agent of malaria

Malaria is caused by parasites of the Plasmodium genus. Four species of Plasmodium can infect humans: P. vivax, P. ovale, P. malariae and P. falciparum. Infection is most commonly caused by P. vivax or P. falciparum, the latter causing the most severe form of malaria. A fifth species, the simian parasite P. knowlesi, has recently been found to be a major cause of human malaria in Malaysian Borneo, and the disease has also been reported from southern and eastern Asia. Mixed infections may occur.

Identification of malaria

Clinical features

The most prominent feature of malaria is fever. The classic symptoms of fever with a regular recurring pattern every 2 to 3 days is not usually present when the disease begins. Irregular fever also may occur due to mixed infections, ineffective use of prophylactic drugs and partial treatment. Patients commonly feel well on the days when fever is absent. A presumptive diagnosis of malaria should be made for any person with a high fever who has been to a malarious area, particularly when that travel was recent.

Early diagnosis with prompt appropriate treatment is essential, as malaria can be a fatal disease. If the initial blood film is negative for malarial parasites, the test should be repeated within 12 to 24 hours and preferably when the person’s temperature is rising. One negative test does not exclude the diagnosis, particularly if the patient has taken antimalarials, which may result in partial treatment of the infection.

Rapidly rising temperature is commonly associated with rigors (shaking chills), muscle pains, back pain, nausea and headache. The episode frequently ends with profuse sweating. Other symptoms may include confusion or other neurological signs, diarrhoea, dark urine, jaundice, cough and respiratory distress.

Severe complications, usually with P. falciparum infections, can include coma, acute encephalopathy, cerebral oedema, vomiting, renal failure, severe anaemia, thrombocytopenia, pulmonary oedema, shock, acidosis, coagulation defects, respiratory failure, liver failure and death. Case-fatality rates in non-immune people may be 10 to 40 per cent without treatment.

Atypical presentations that can occur predominantly involve a diarrhoeal illness and have resulted in delayed diagnosis and death. Other infections, such as the bacterial infection, typhoid fever, may occur concurrently. Such infections should be looked for, especially if the patient fails to respond well to appropriate treatment.

Individuals who are partially immune or who have been taking antimalarial chemoprophylaxis may show an atypical clinical picture with wide variations in the incubation period.

Malaria due to species other than P. falciparum is generally not life-threatening except in the very young, the very old and those with immunodeficiency or other concurrent disease.

Malaria poses a serious threat to pregnant women, as it can compromise foetal development, possibly resulting in premature labour or miscarriage. Pregnant women should be advised to avoid travel to malarious areas if possible. Similarly, malaria presents considerable risks for children, particularly the very young, and the choice of suitable drugs is limited. Mosquito avoidance measures should be emphasised.

Diagnosis

Malaria can be diagnosed by demonstration of malaria parasites in blood films. Blood samples should be sent to a laboratory with experience in the diagnosis of malaria by the use of thick and thin films. Repeated examination may be necessary due to variations in the density of the parasites. Confirmation of the species should be sought from a reference laboratory.

Incubation period of Plasmodium

The time between an infectious mosquito bite and the first detection of parasites in a blood smear is generally 6 to 16 days. Symptoms may not occur at that time, and the first presentation of the infection may be delayed for weeks or months. Commonly, clinical symptoms occur after 7 to 14 days for P. falciparum, 7–30 days for P. malariae and 8 to 14 days for P. vivax and P. ovale.

Suboptimal suppression with prophylactic drugs may delay the clinical presentation, and transmission by blood transfusion usually results in a shorter incubation period.

Public health significance and occurrence of malaria

Malaria has historically been endemic in Australia but was declared eradicated from the country in 1981. Although it is no longer endemic, approximately 700–800 cases occur each year in Australia in travellers infected elsewhere. The region of northern Australia north of 19°S latitude is the receptive zone for malaria transmission. Occasional cases of local transmission occur in the Torres Strait islands and rarely in northern Queensland, and vigilance is required to prevent re-establishment of the infection in some northern localities. Recently, the countries most commonly associated with malaria imported to Australia have been Papua New Guinea, East Timor and Indonesia.

Incidence in Victoria is a function of the number of travellers to or arrivals from endemic areas and the extent to which preventive measures are undertaken. All notified cases of malaria in Victoria have been acquired overseas. They have included returned travellers, people visiting friends and relatives and humanitarian arrivals. Between 2004 and 2008, an average of 100 confirmed cases of malaria (range: 63 to 117 cases) were notified annually in Victoria.

Globally, the disease is endemic in areas of Asia, Africa and Central and South America, with the highest transmission in sub-Saharan Africa. Generally, in warmer regions closer to the equator, transmission is more intense, malaria is transmitted year-round, and P. falciparum predominates. The global distribution of per capita gross domestic product (GDP) shows a striking correlation between malaria and poverty, and malaria-endemic countries also have lower rates of economic growth. Malaria costs Africa an estimated $12 billion in lost GDP every year.

An estimated 216 million new infections occurred in 2010; there were an estimated 655,000 deaths, mostly of children under 5 years and in sub-Saharan Africa.

Reservoir for Plasmodium

Humans.

Mode of transmission of Plasmodium

A female Anopheles mosquito ingests gametocytes from an infected human. The parasite must undergo 8–35 days of development within the mosquito before infective sporozoites are formed. The sporozoites are transmitted to another person via the bite of an infected mosquito. In rare cases, malaria parasites can be transmitted blood-to-blood from one person to another without requiring passage through a mosquito (from mother to child in ‘congenital malaria’ or through transfusion, organ transplantation or shared needles).

Period of communicability of malaria

Infected cases may remain infectious if untreated or inadequately treated so that gametocytes persist. Relapse can occur in the case of infection with P. ovale and P. vivax, involving the re-emergence of blood-stage parasites from latent parasites (hypnozoites) in the liver. The infected mosquito remains infected for life.

Susceptibility and resistance to malaria

People travelling to malarious areas are at risk.

Control measures for malaria

Preventive measures

Travellers should be advised of the four principles of malaria protection:

• Be aware of the risk, the incubation period and the main symptoms.
• Avoid being bitten by mosquitoes, especially between dusk and dawn.
• Take antimalarial drugs (chemoprophylaxis) to reduce the risk of infection, where appropriate.
• Immediately seek diagnosis and treatment if a fever develops 1 week or more after entering an area where there is a malaria risk.

Personal protection against mosquito bites remains the first line of defence against malaria. Measures to recommend include:

• avoiding mosquito-prone areas, particularly at dusk and dawn
• ensuring that accommodation is mosquito-proof (using mosquito nets, flying insect spray, mosquito coils or plug-in insecticide mats in rooms)
• using personal repellents containing diethyl toluamide (DEET) or picaridin
• wearing long, loose-fitting, light-coloured protective clothing.
• prevalence and type of resistance of the malarial parasite to the available drugs
• level of malaria transmission
• duration and place of stay, particularly in rural areas
• intensity of vector mosquito contact
• availability of adequate healthcare
• age
• traveller’s current health and medical history
• risk of traveller not complying with recommendations.

There is no drug that is completely safe and completely effective for prophylaxis against malaria. The decision to recommend chemoprophylaxis and the choice of drug(s) must involve an analysis of the risks and benefits based on the following considerations:

Almost all prophylactic drugs should be taken with unfailing regularity for the duration of the stay in the malaria risk area and be continued for four weeks after the last possible exposure to infection, as parasites may still emerge from the liver and cause disease during this period. The single exception is atovaquone/proguanil, which can be stopped one week after return. Over-reliance on chemoprophylaxis (above other preventive measures) is ill-advised, as the malaria parasite’s drug resistance continues to change.

There is no scientific proof that homoeopathic or ‘natural’ remedies are effective in either preventing or treating malaria; therefore, they should not be recommended for travellers to malarious areas.

Malaria poses a serious threat to pregnant women, as it can compromise foetal development, possibly resulting in premature labour or miscarriage. Pregnant women should be advised to avoid travel to malarious areas if possible. Similarly, malaria presents considerable risks for children, particularly the very young, and the choice of suitable drugs is limited. Mosquito avoidance measures should be emphasised.

There is no vaccine available, although vaccines are currently under development and show some promise in reducing severe cases of malaria in endemic regions.

Control of case

Isolation of the case is not required. Mosquito contact with the patient should be prevented, especially in tropical areas of Australia where mosquitoes capable of transmitting the disease are present. The country of acquisition of the disease should be determined. It is important to exclude acquisition within Australia or from an unusual source, such as a blood transfusion, that would need further investigation.

Treatment is complex, and advice should be sought from an infectious disease physician. Artemisinin-based combination therapy (ACT) is now recommended by the World Health Organization as first-line treatment in most countries with malaria transmission. Most strains of P. falciparum today are resistant to chloroquine but are almost universally sensitive to ACT, although ACT-resistant P. falciparum has been identified on the Thailand–Cambodia border. Only P. falciparum contracted in some parts of China, Central America and the Middle East is still sensitive to chloroquine. P. vivax, P. ovale and P. malariae are sensitive to chloroquine, but P. vivax resistant to chloroquine has been found in Irian Jaya, Myanmar, Papua New Guinea and Vanuatu. P. knowlesi responds rapidly to ACT.

If the species cannot be identified with confidence, the patient should be treated as for the most serious infection with P. falciparum. Although primaquine reduces the risk of relapses of disease, relapses can occur.

Control of contacts

Travelling companions or recipients of any blood transfusion from the case should be warned that they may also be at risk of developing the disease and should seek help promptly if suggestive symptoms develop.

Control of environment

Not applicable, as Victoria’s ecology is unlikely to sustain endemic malaria, although this is possible in northern areas of Australia.

Outbreak measures for malaria

Any outbreaks of malaria in Australia require immediate public health interventions.