Navigating malaria at sea: Why prevention requires a rethink

The most dangerous animal in the world is not what most would expect. It isn’t the shark, the snake, or any of the creatures typically associated with risk—it’s the mosquito. Responsible for over 600,000 deaths annually from malaria alone, it remains the most lethal creature on the planet [1]. For those working at sea, particularly in tropical regions, this threat is a very real occupational hazard.

Each year, World Malaria Day reminds us that while malaria is preventable, it continues to affect vulnerable populations.

A persistent risk in maritime operations

Seafarers often operate in regions where malaria is endemic. Although vessels spend much of their time offshore, risk arises during port calls or anchorages where mosquitoes can come aboard and transmit infection [2].

In 2014, the Republic of the Marshall Islands (RMI) issued a Marine Safety Advisory after reporting five onboard malaria cases—four of them fatal. Symptoms were misread as flu-like, delaying treatment until it was too late [3]. The advisory urged improved crew training, better access to antimalarial medication, and clinical guidance tailored to maritime operations. These recommendations reflect an evolving need for structured, ship-specific medical support—well beyond basic first aid.

When prevention causes issues: A real-world case

On board a vessel preparing for arrival in Ivory Coast, a group of healthy male seafarers—ages 25 to 42—began malaria chemoprophylaxis using Eloquine (mefloquine 250mg). None had significant medical history.  Shortly after initiating the weekly prophylaxis, four of them reported significant mental and physical side effects.

Symptoms included severe fatigue, insomnia (with sleep limited to 2–3 hours per night), abdominal and leg pain, vomiting, headaches, shortness of breath, and in one case, increased nervousness in a seafarer with a history of thyroid surgery. Another experienced transient facial swelling. These symptoms quickly raised concerns, and the ship’s master contacted shore-based medical support to seek advice.

Given the nature and severity of the complaints, all affected seafarers were advised to immediately discontinue Eloquine. Since no alternative prophylactic medication (such as Malarone) was available on board at the time, the seafarers continued without malaria protection for the remainder of the voyage through the risk zone. They were provided with supportive medication from the vessel’s pharmacy to manage symptoms such as insomnia, anxiety, and gastrointestinal discomfort.

Although the crew was monitored closely, the symptoms persisted for over a month. Eventually, once Malarone became available, all affected seafarers were started on the new regimen. The transition was well tolerated, and no further adverse effects were reported.

This case was managed in close coordination with Health4Crew’s maritime medical team, who provided real-time clinical advice. It demonstrates how quickly a preventive measure can become a health risk—especially without access to diversified pharmaceutical options or expert oversight at sea.

Understanding the risks of Mefloquine

Mefloquine is used for its weekly dosing and effectiveness, but carries well-documented risks: neuropsychiatric side effects such as anxiety, depression, agitation, sleep disruption, and—rarely—psychosis or lasting neurological changes [4][5].

Physical side effects are less discussed but equally impactful: abdominal pain, muscle aches, dizziness, headaches, nausea, and shortness of breath [6]. These symptoms, while not life-threatening, can compromise a seafarer’s ability to focus, rest, and operate safely.

Safer alternatives to consider

Two common alternatives include:

1. Doxycycline: a daily antibiotic with good tolerability, though it may cause sun sensitivity and mild stomach upset [7].
2. Atovaquone-proguanil (Malarone): a once-daily pill with few side effects, ideal for short-to-mid duration voyages [8].

Medical guidelines now prioritize individual risk assessments, particularly for those in high-stress or safety-critical roles. In such cases, medications with known psychiatric side effects should be used with caution—or avoided entirely.

Health at sea is not one-dimensional

Maritime health strategies have traditionally focused on disease prevention as a physical challenge. But the reality is more complex. A seafarer who is exhausted, nauseated, or anxious is not functioning at full capacity—even if technically disease-free.

Health decisions must reflect the interconnected nature of physical and mental wellbeing. When prophylactic medications impair alertness, cognitive function, or emotional balance, they risk undermining both safety and morale on board.

Malaria itself and some antimalarial drugs can—rarely—trigger psychosis. By understanding the risks, watching for early symptoms, and knowing exactly how to act onboard, you can keep both your body and mind healthy while sailing through malaria zones.

Recognizing warning signs

Mental health changes often begin subtly. Warning signs include:

Spotting these signs early in yourself or a crewmate is essential to prevent escalation.

Practical steps for seafarers managing mental health symptoms

Beyond company protocols, individual seafarers can take active measures to maintain mental wellbeing:

• Self-monitor daily : note sleep patterns, energy levels, and any unusual thoughts or emotions.
• Practice quick relief techniques: practice 2-3 breathing cycles  or  use of grounding techniques when feeling overwhelmed
• Maintain routine: stick to regular sleep and meal schedules, even in busy port calls. Engage in short physical activities on deck to boost mood.
• Stay connected:  reach out to your assigned buddy at least once daily for an honest check-in.  Share concerns or odd experiences immediately; don’t wait for morning briefings.
• Plan for rest periods: coordinate with colleagues to ensure you can take breaks when needed. Use rest times to practice relaxation exercises away from high‑noise areas.
• Use your resources: keep psychoeducation materials and  toolkits at hand (e.g., stress ball, guided imagery scripts).

By integrating these personal steps with shipboard support systems, you’ll be better equipped to protect your mental health—even when malaria and its treatments challenge your resilience.

Building better prevention policies

The lessons from this case and others point to a need for more comprehensive malaria prevention protocols that include:

• Individual risk assessment: Review each crew member’s medical and mental health history prior to prescribing chemoprophylaxis.
• Clear education: Educate crews about potential drug potential side effects, warning signs, and when to report them.
• Psychoeducation briefings: Hold short group sessions explaining how malaria and its treatments can affect thoughts and feelings. Use simple handouts or posters in common areas listing potential symptoms and coping tips.
• Availability of alternative antimalarials on board: Stock multiple antimalarial medications and supportive treatments to allow individualized regimens.
• Protocols for symptom management and reporting: Train crew members to self-monitor and use daily mood logs to flag any warning signs.  Assign a trained buddy or officer to monitor and initiate medical consultation protocols, in cases of moderate to severe.
• Immediate supportive measures: Adjust the environment; ensure a quiet space, hydration, light snacks, and provide relaxation tools.
• Telemedical support to guide decision-making in real time to evaluate and adjust medication, dose timing, compliance or combination with other medication. If severe psychosis persists coordinate with telemedical provider to determine urgency and destination port facilities.

By shifting from a one-size-fits-all approach to a more nuanced model of care, ship operators and clinicians can help ensure malaria prevention doesn’t come at the expense of crew wellbeing.

Looking ahead

Effective prevention is more than distributing tablets. It requires foresight, flexibility, and above all, a commitment to the total health of the seafarer.

As the global maritime community marks World Malaria Day, it’s time to expand our understanding of risk—not just from the disease, but from the interventions we use to fight it. In doing so, we can ensure that no crew member must choose between protection and wellbeing while navigating the world’s oceans.

The views presented are only those of the authors and do not necessarily reflect those of SAFETY4SEA and are for information sharing and discussion purposes only.

References

1. World Health Organization (2023). World Malaria Report. https://www.who.int/news-room/fact-sheets/detail/malaria
2. Amenta, F. et al. (2019). First surveillance of malaria among seafarers: evaluation of incidence and identification of risk areas. Acta Biomed, 90(S12), 25–30.
3. Republic of the Marshall Islands. (2014). Marine Safety Advisory No. 35-14: Malaria Prevention Advisory.
4. VA Public Health (2021). Mefloquine (Lariam) – Drug Safety Information for Veterans.
5. U.S. FDA (2013). Drug Safety Communication: Mefloquine and Neurologic Side Effects. https://www.fda.gov
6. Lariam (mefloquine hydrochloride) – Summary of Product Characteristics, EMA.
7. Centers for Disease Control and Prevention (CDC). Doxycycline: Malaria Prophylaxis and Treatment.
8. Idnani, R., & Kotlowski, A. (2011). Malaria prevention strategy for seafarers. International Maritime Health, 62(4), 236–242.