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Alarming spike in dengue cases

Dengue is a viral disease transmitted by infected mosquitoes and can be life-threatening. It causes flu-like symptoms and can develop into a potentially lethal complication called ‘severe dengue’. Dengue flourishes in poor urban areas, suburbs and the countryside but can also affect more affluent neighbourhoods in tropical and subtropical countries. The infection rates are higher outdoors and during daytime.

There is no vaccination for dengue, and the best way to prevent it is to protect against mosquito bites. Shipowners and operators with vessels trading to countries with ongoing dengue transmission should therefore ensure that crews are aware of the risks and are able to deal with the various challenges that this disease can bring.

Dengue distribution trends

According to the World Health Organization (WHO), the incidence of dengue has increased 30-fold over the last 50 years. Before 1970, only nine countries had seen severe dengue epidemics. Now, up to 50-100 million infections are estimated to occur annually in over 100 endemic countries, putting almost half of the world’s population at risk.

Not only is the number of cases increasing as the disease spreads to new areas, but explosive outbreaks are also occurring. According to a report issued by the European Centre for Disease Prevention and Control (ECDC) on 20 September 2019, countries such as Brazil, Thailand, the Philippines, Cambodia and Vietnam have experienced substantial increases in the number dengue cases compared to the same time period in 2018. The WHO also reports of dengue outbreaks in Congo, Côte d’Ivoire and Tanzania and emphasizes that the threat of a possible outbreak of dengue fever now exists in Europe as well. As at 1 October 2019, three locally acquired (autochthonous) cases of dengue have been reported in France and Spain. However, the ECDC considers the likelihood of further local sustained transmission to be very low in both countries as environmental conditions will become progressively less suitable for transmission during autumn.

Symptoms to look out for

A seafarer infected by dengue may initially experience fever with mild non-specific symptoms like those of influenza and other febrile illnesses. However, according to the WHO, dengue can be suspected when a high fever (40°C/ 104°F) is accompanied by at least two of the following symptoms:

Symptoms usually last for 2-7 days, following an incubation period of 4-10 days after a bite from an infected mosquito.

Severe dengue is a potentially fatal complication due to plasma leaking, fluid accumulation, respiratory distress, severe bleeding, or organ impairment. The warning signs to look out for occur 3-7 days after the first symptoms in conjunction with a decrease in temperature (below 38°C/ 100°F) include severe abdominal pain, persistent vomiting, rapid breathing, bleeding gums, blood in vomit, fatigue and restlessness. The next 24-48 hours of the critical stage can be fatal and proper medical care is needed to avoid complications and the risk of death.

Precautions for ships trading within mosquito zones

Prior to visiting affected areas:

• Monitor the WHO website and similar sources for official advice regarding any ongoing outbreaks. Contact a medical practitioner if in doubt.
• Review all the ports to be visited in that area and evaluate the risk. Consider the length of stay in an affected area, time spent at sea, in port, on rivers, etc., as well as planned shore leave by the crew.
• Inform the crew about the risks present and the precautions to be taken as well as actions to be taken if illness occurs at sea. Stress that a headache, fever and flu-like symptoms are always grounds for contacting the medical officer.
• Ensure sufficient supplies onboard of effective insect repellents (e.g. those containing DEET, picaridin or IR3535), light coloured boiler suits, porthole/door mesh screens and bed-nets.

During a visit to affected areas:

• Implement measures to prevent mosquito bites, including:
o keep all openings closed and operate air conditioning at all times;
o stay indoors, in accommodation and engine room areas, as much as possible;
o wear loose-fitting light-coloured clothes when proceeding onto the deck and other open areas;
o use effective insect repellents on exposed skin and/or clothing as directed on the product label; and
o when using a sunscreen, apply sunscreen first, followed by repellent.
• Remove pools of stagnant water, dew or rain to prevent the vessel creating its own mosquito breeding grounds.
• Pay particular attention to wet areas of lifeboats, coiled mooring ropes, bilges, scuppers, awnings and gutters. “Even a bottle cap can contain enough water for a mosquito to breed!” says the WHO.
• Use an insecticide spray to eradicate mosquitos found inside accommodation or other areas.

After a visit to affected areas:

• Seek medical advice over the radio if dengue is suspected on board. Normally the vessel is in port only for a short time and will most probably be back at sea when symptoms are noticed due to an incubation period of several days.
• Place the patient under close observation and undertake the required onboard treatment, preferably in close co-operation with a medical doctor.
• The patient should rest and drink plenty of fluids. Paracetamol can be taken to bring down any fever and to reduce joint pains. Aspirin, ibuprofen, or other NSAIDs should not be taken since they can increase the risk of bleeding.
• Medical evacuation may be the only solution if the patient’s condition does not improve.

Depending on the area of trade, the risk of exposure related to other mosquito-borne diseases, such as malaria, yellow fever, chikungunya and zika, should also be taken into account when planning voyages.

Further information

Prevention requires vigilance so stay up to date! Here are some recommended sources of information:

• Detailed information about malaria and other mosquito-borne diseases – their characteristics, treatment, prevention, geographical distribution and recent outbreaks – are available via WHO’s “Health topics”.
• The United States Centers for Disease Control and Prevention (CDC) provides similar information via its “Disease & Conditions A-Z Index”.
• The CDC’s general “Destination List” is a good starting point for a voyage specific risk assessment related mosquito-borne diseases.
• The European Centre for Disease Prevention and Control (ECDC) regularly issues Communicable Disease Threat Reports.
National governments may also publish safety alerts concerning seasonal outbreaks of the diseases on their “safe travel” websites. Relevant information can also be obtained from medical doctors and local vaccination offices.
Source: Gard (http://www.gard.no/web/updates/content/28463011/alarming-spike-in-dengue-cases)

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