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Article: The threat of Malaria

06 February 2020

Nigel Griffiths heads the Marine Advisory Medical Service and has administered the Standard Club PEME Scheme for two years. Here he shares information about Malaria, measures of prevention and how it can be treated. 

Malaria

Malaria is a mosquito-borne infectious disease that affects humans and other animals. Malaria causes symptoms that typically include fever, tiredness, vomiting, and headaches. In severe cases it can cause yellow skin, seizures, coma, or death. According to the latest World Malaria Report by WHO, released in November 2018, there were 219 million cases of malaria in 2017, up from 217 million cases in 2016. The estimated number of malaria deaths stood at 435 000 in 2017, a similar number to the previous year.

Malaria is transmitted through the bites of female Anopheles mosquitoes. There are more than 400 different species of Anopheles mosquito; around 30 are malaria vectors of major importance. All of the important vector species bite between dusk and dawn. The intensity of transmission depends on factors related to the parasite, the vector, the human host, and the environment. The mosquitoes lay their eggs in water, which hatch into larvae, eventually emerging as adult mosquitoes. The female mosquitoes seek a blood meal to nurture their eggs. Each species of Anopheles mosquito has its own preferred aquatic habitat; for example, some prefer small, shallow collections of fresh water, such as puddles and hoof prints, which are abundant during the rainy season in tropical countries.

Transmission is more intense in places where the mosquito lifespan is longer (so that the parasite has time to complete its development inside the mosquito) and where it prefers to bite humans rather than other animals. It also depends on climatic conditions that may affect the number and survival of mosquitoes, such as rainfall patterns, temperature and humidity. In many places, transmission is seasonal, with the peak during and just after the rainy season. Malaria epidemics can occur when climate and other conditions suddenly favour transmission in areas where people have little or no immunity to malaria. Seafarers coming from countries in which the disease is non prevalent, are especially susceptible to infection.

After being bitten by an infected mosquito, with only one bite required for the parasite to be passed from mosquito to human, malaria symptoms can appear after seven days, but more usually after 10 to 15 days. In some cases, however, it may take up to 12 months or longer for malaria to manifest itself, especially when anti-malaria medications have been taken; therefore seafarers who experience any of the following symptoms after leaving a malaria affected area should seek immediate medical assistance.

Malaria symptoms may initially be mild and flu-like including headache, a high temperature of 38˚C (100.4˚F), muscle pains, sweats and chills in cycles, vomiting and diarrhoea. Often the symptoms may not be attributed to Malaria, however, in some cases the patient’s condition may deteriorate quite rapidly and complications can develop within hours of a severe attack of malaria, therefore prompt medical attention or advice is essential to determine if malaria is the cause so that treatment can be started immediately.

The global burden of mortality is dominated by countries in sub-Saharan Africa, with Nigeria and the Democratic Republic of the Congo together accounting for more than 35% of the global total of estimated malaria deaths, although it should be noted that India ranks third for the number of malaria cases and number of deaths.

Prevention

Vector control is the main way to prevent and reduce malaria transmission. Two forms of vector control – insecticide-treated mosquito nets and indoor residual spraying – are effective in a wide range of circumstances.

Antimalarial medicines can also be used to prevent malaria. For seafarers, malaria can be prevented through chemoprophylaxis (medication), which suppresses the blood stage of malaria infections, thereby preventing malaria disease.

Prior to proceeding to a Malaria affected area, it is recommended that a risk assessment be conducted as, even in areas where malaria exists, the risk may be very low and the taking of prophylactic anti-malaria drugs may not be deemed necessary, and expert advice should be sought in this regard.

Chemoprophylaxis

Anti-malaria drugs can help prevent as well as treat malaria. The recommended anti-malaria prescription may consist of one of more different drugs and its composition will depend on the area visited. Advice should therefore be sought from medical professionals to determine the most effective course of tablets which should be taken by crewmembers travelling to a affected area.

A course of anti-malaria tablets should be taken in accordance with the manufacturers’ instructions. Usually the course of tables will start prior to travelling, be taken for the duration of the visit to a malaria affected area, and then taken for one or more weeks after leaving. It is important that the treatment periods prior to and after being in a malaria affected area and the recommended dosages are strictly adhered to. Often people will forget to take their tablets after leaving an affected area, or they will consider that as they have not fallen ill while in a malaria zone, that it is safe to stop taking their tablets early. This is not the case.

The areas visited will dictate the recommended anti-malaria treatment as the P. falciparum parasite is resistant to chloroquine in many areas, and resistance to artemisinin is found in a number of South East Asian countries. Common anti-malaria treatments involve Mefloquine (Larium), Doxycycline and / or Atovaquone / Proguanil (Malarone). However, a number of these drugs may cause side effects which should also be considered when evaluating the most suitable therapy for a given area:

• Mefloquine (Larium) – dizziness, headache, insomnia, nightmares, anxiety, depression, panic attacks and hallucinations. Although an effective drug, due to the various side effects it is deemed by medical experts to be an inappropriate drug for seafarers.
• Doxycycline – sunburn due to light sensitivity, upset stomach, heartburn and thrush.
• Atovaquone / Proguanil (Malarone) – upset stomach, headaches, rashes and mouth ulcers.
When considering the foregoing anti-malaria treatments, medical professionals recommend that Atovaquone / Proguanil (Malarone) should be the primary drug to be considered for use by seafarers.

Some anti-malaria drugs may also affect a person’s ability to operate machinery. Therefore when selecting the anti-malaria regime it should be ensured that these will not affect the crew’s ability to carry out their work safely.

As a general guide, crewmembers should note the WHO five principles of Malaria management  – the ABCDE – of malaria protection:

• Be Aware of the risk, the incubation period, the possibility of delayed onset, and the main symptoms.
• Avoid being Bitten by mosquitoes, especially between dusk and dawn.
• Take antimalarial drugs (Chemoprophylaxis) when appropriate, at regular intervals to prevent malaria attacks.
• Immediately seek Diagnosis and treatment if a fever develops one week or more after entering an area where there is a malaria risk and up to three months (or, rarely, later) after departure from a risk area.
• Avoid outdoor activities in Environments that are mosquito breeding places, such as where there is standing water, especially in late evening and at night.

Nigel Griffiths heads the Marine Advisory Medical Service and has administered the Standard Club PEME Scheme for two years. Nigel is a graduate of the Law School of the University of Glasgow, holding a specialist Masters Degree in Medical Law. Nigel is also a nurse, holding registrations in both general and psychiatric nursing and the diploma aeromedical nursing from the royal college of nursing in the UK.