Malaria

Victorian statutory requirement

Malaria (Group B disease) must be notified in writing within five days of diagnosis.

School exclusion is not required.

Infectious agent

Malaria is caused by parasites of the Plasmodium spp. Four species of Plasmodium (P.) 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. Mixed infections may occur.

Identification

Clinical features
The most prominent feature of malaria is fever. Classic descriptions of fever with a regular recurring pattern every two or three 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 until proved otherwise, particularly with recent travel.

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 it should be repeated within12–24 hours and preferably when the temperature is rising. One negative test does not exclude the diagnosis, particularly if the patient has taken antibiotics which may result in partial treatment of the infection.

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

The following severe complications may occur, usually with P. falciparum infections: 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 10–40%.

Atypical presentations can occur which 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. These should be looked for, especially if the patient fails to respond well to appropriate treatment.

Individuals who are partially immune or have been taking anti-malarial 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, very old and those with immunodeficiency or other concurrent disease.

Method of 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 density of parasites. Confirmation of the species should be sought from a reference laboratory.

Incubation period

The time between an infectious mosquito bite and the first detection of parasites in a blood smear is generally 6–16 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 7–14 days for P. falciparum, 7–30 days for P. malariae and 8–14 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 & occurrence

The malaria situation worldwide is deteriorating. There are increasing levels of transmission and it has returned to areas where it had previously been eradicated. Drug resistance has increased and there has been a spread of vector resistance to insecticides.

An estimated 220 million new infections a year occur worldwide. The disease is endemic in areas of Asia, Africa and Central and South America.

The World Health Organization certified Australia free of endemic malaria in 1981 but several hundred imported cases are recorded each year. However the region lying north of a line joining Townsville on the east coast and Port Hedland on the west coast remains receptive and vulnerable to the re-establishment of the disease. This is due to the presence of known or suspected vectors, suitable environmental conditions and the continual arrival of malaria-infected travellers.

Many cases occur among migrants who become infected after re-visiting their native country after a delay of many years when they may have lost their immunity. In Victoria, all malarial patients in recent times have provided travel histories which include countries with endemic malaria. Recently, the countries most commonly associated with imported malaria have been Papua New Guinea, East Timor and Indonesia.

Reservoir

Humans.

Mode of transmission

A female Anopheles mosquito ingests gametocytes from an infected human. The parasite must undergo 8–35 days of development within the mosquito before the infective sporozoites are formed. The sporozoites are transmitted to another person via the bite of an infected mosquito.

The disease may also be transmitted by blood or congenitally in untreated or inadequately treated cases.

Period of communicability

Infected cases may remain infectious for years if untreated or inadequately treated so that gametocytes persist. The infected mosquito remains infected for life.

Susceptibility & resistance

People traveling to malarious areas are at risk.

Control measures

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 suppress infection where appropriate
immediately seek diagnosis and treatment if a fever develops one 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 outdoor exposure between dusk and dawn
wearing long, loose clothing after dusk, preferably in light colours
avoiding perfumes and colognes
using effective insect repellents, for example products containing up to 20% DEET
using knock-down sprays, mosquito coils, or plug-in vaporising devices indoors
using mosquito nets, preferably pre-treated with an appropriate insect repellent.
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:

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 health care
age
traveller’s current health and medical history
risk of traveller not complying with recommendations.

All prophylactic drugs should be taken with unfailing regularity for the duration of the stay in the malaria risk area and should 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 is ill-advised as drug resistance by the malaria parasite continues to change.

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.

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. Most strains of P. falciparum today are resistant to chloroquine. Only P. falciparum contracted in some parts of China, Central America and the Middle East are 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.

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

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

Infectious diseasesepidemiology and surveillance

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