In a statement of 18 November 2016, the WHO declared an end to the Public Health Emergency of International Concern (PHEIC) regarding Zika, when the causal link between the mosquito borne Zika virus and extraordinary clusters of microcephaly and other neurological disorders was established. At the same time, the statement also makes it clear that Zika remains a significant and enduring global health threat, see also the Director-General of WHO’s commentary “Zika: We must be ready for the long haul” on 1 February 2017.

Zika has joined the class of mosquito-borne diseases that have the potential to cause severe health implications for seafarers. Other mosquito-borne diseases in this class include malaria, dengue, yellow fever and chikungunya. It is important that shipowners and operators safeguard crew through awareness of recent areas of outbreak of these diseases as well as prevention measures including education of crew.

The global burden

Mosquitoes are one of the deadliest animals in the world, according to the WHO. Their ability to carry and spread disease leads to millions of deaths every year. Zika recently emerged as one of the most challenging threats to human health, but it is also worth noting malaria, dengue, which can develop into a potentially lethal complication known as Dengue Haemorrhagic Fever (DHF), yellow fever and chikungunya.

Locating the danger

Major trade routes pass through areas affected by mosquito-borne diseases putting seafarers at risk. Up to date official advice should be checked, every time a vessel is destined for areas, where there is a potential risk of mosquito-transmitted diseases.

Zika has now spread to a large number of countries in the Americas, as well as some Pacific Islands and countries in Southeast Asia. Malaria is found in tropical and subtropical areas of Africa, Asia, the Middle East and Central and South America. The spread of dengue has grown dramatically in recent decades and it is now found in tropical and sub-tropical climates worldwide, mostly in urban and semi-urban areas. Chikungunya is found mainly in Africa, Asia and the Indian subcontinent and has also spread to Europe and the Americas in recent decades. Yellow fever is found in tropical areas of Africa and Central and South America.

The nature of the diseases

The mosquito that transmits malaria, the Anopheles mosquito, is active mainly at night, between dusk and dawn. Zika, dengue, chikungunya and yellow fever, on the other hand, are primarily transmitted through the bites of an infected Aedes mosquito, which also bites during daylight hours. Zika can also be sexually transmitted from one person to another.

A seafarer infected by any of the common mosquito-borne diseases may initially experience fever with mild non-specific symptoms similar to those of influenza and other febrile illnesses. However, as severity and treatment varies between the diseases, immediate medical attention should be sought to ensure early diagnosis. Information that may assist in diagnosis has also been published by the WHO and is reproduced below.

Port control measures


Evidence suggests that mosquito-borne diseases spread internationally primarily through infected people. Disinsection of vessels is therefore considered not to be a very effective mechanism to prevent the importation of infected mosquitos. Nevertheless, some countries may still require proof of disinsection of vessels and/or cargo arriving from affected areas. Disinsection,, in this case, means eradicating live mosquitoes, their larva, and eggs and should not be confused with disinfection.

Both China and South Korea implemented such requirements in March 2016, in order to control Zika virus transmission in to their countries. However, as of March 2017, both countries have announced that disinsection of vessels arriving from Zika affected areas is no longer required. 

Changes to yellow fever vaccination certificates

The International Health Regulations (IHR) are an international legal instrument that is binding on 196 countries across the globe, including all the Member States of WHO. Yellow fever is the only disease listed in the IHR for which countries may require proof of vaccination from travellers, including seafarers, as a condition of entry.

Amendments to the IHR entered into force on11 July 2016, and from this date, the certificate of vaccination against yellow fever is valid for the life of the person vaccinated. Revaccination or a booster dose of yellow fever vaccine every 10 years will no longer be required for entry into an IHR State Party and valid IHR international certificates of vaccination are now automatically valid for life of the person indicated. According to the WHO, no modifications are necessary to an existing certificate. Indeed under the IHR, any changes, deletions, erasures or additions may cause a certificate to be rendered invalid. 

Recommended precautions

Shipowners and operators with vessels trading within mosquito zones should ensure that these vessels are able to deal with the various challenges that a mosquito-borne disease can bring. In addition to the duty of care for those onboard, shipowners and Masters also have a responsibility for taking measures to prevent such diseases from being passed on. Members and clients are therefore advised to, as far as practicable, tailor make their own strategies for dealing with risks associated with mosquito-borne diseases and the following should be considered:

Prior to visiting affected areas

  • Continuously 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 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 leaves by the crew.
  • Inform the crew about the risks 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 of effective insect repellents (e.g. hose containing DEET, picaridin or IR3535), light colored boiler suits, porthole/door mesh screens and bed-nets.
  • Evaluate, in close co-operation with a medical doctor and based on the vessel’s expected exposure time in an affected area, if the crew should take an anti-malarial drug.
  • Ensure that all crew members carry valid yellow fever certificates. As a precaution, check with the vessel’s agent that local port health inspectors are aware of their country's official position regarding yellow fever vaccination requirements and will recognise the amended IHR and yellow fever vaccinations with lifetime validity.

During a visit to affected areas

  • Implement measures to avoid mosquito bites, e.g. wear protective clothing, stay in air-conditioned screened accommodation areas, use bed-nets in sleeping areas. Use effective insect repellents on exposed skin and/or clothing as directed on the product label and when using a sunscreen, the recommendation is to apply sunscreen first, followed by repellent.
  • If crew members are taking anti-malarial drugs, implement a method of control to ensure they take the medication at the prescribed times, e.g. via a log book.
  • Remove pools of stagnant water, dew or rain in order for the vessel not to create its own mosquito breeding grounds. Pay particular attention to areas such as lifeboats, coiled mooring ropes, bilges, scuppers, awnings and gutters.
  • As some countries may require proof of disinsection (mosquito eradication) of vessels and/or cargo issued prior to leaving an affected area, contact the vessel’s agent in the next port of call to ascertain the local quarantine requirements in force and the documentation required.

After a visit to affected areas

  • Seek medical advice over the radio, particularly if malaria or 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. Avoid use of NSAIDs unless dengue can be ruled out. Evacuation may be the only solution if the patient’s condition does not improve.
  • As a Zika infection during pregnancy can cause microcephaly, i.e. babies born with small heads, all seafarers concerned about a pregnancy, males and females, are advised to consult a health care provider for counseling after possible exposure to Zika virus.

Source & Image credit: Gard P&I Club