Infections in this cluster are transmitted by animals (zoonotic) or from agents in water and soil (environmental). Shipping is associated with the potential threat of dispersal of microbes and their vectors, such as rodents and arthropods including cockroaches, mites or mosquitoes.  The International Health Regulations 2005 of the World Health Organization regulates surveillance of disease, disinfection, deratting and disinsection of ships and port areas as well as transported goods and health measures of travellers including yellow fever vaccination. While the convention aims at the protection of the public health the seafarer is at risk from infected vectors present at the ports of destinations or on board ships. Also, seafarers are affected by protective measures such as vaccinations and disinfection.
Malaria - Human-infective Plasmodium species
Malaria is transmitted by various species of Anopheles mosquitoes. For centuries seafarers have known to be at risk when sailing to malarious coasts.
Most malaria is transmitted by the bite of an infected female Anopheles mosquito. This species occurs in many tropical and subtropical countries (see map at www.who.int/ith/en).
For up-to date information about the risk of acquiring malaria in a given port, see also www.cdc.gov/travelregionalmalaria/index.htm.
The period between the infective bite and the appearance of clinical symptoms is typically 9-14 days for Plasmodium falciparum, 12-18 days for plasmodium vivax and plasmodium ovale and 18-40 days for plasmodium malariae. Some strains of plasmodium vivax may have an incubation period of up to 12 months.
Seafarers and international travellers are at risk of developing severe malaria once infected because they are non-immune and are frequently diagnosed late or are misdiagnosed when returning home. Clinical manifestations of disease may be evident on board when no medical doctor is available for diagnosis and treatment or in ports where the reliability of diagnosis is unknown to the seafarer. Seafarers may develop symptoms when they have ended their contract and returned to their home countries, sometimes to places were malaria is not endemic and thus physicians may not consider malaria when a sailor presents with symptoms of fever, chills, diarrhoea, headache, fatigue or anorexia. Often, specialist tropical and diagnostic tools will not be easily available in the home areas of sailors.
Numerous studies have investigated malaria among seafarers. Mouchtouri et al. concluded from these studies a varied incidence rate from 3 to 12/1000 seafarers.
Tomaszunas estimated the total number of malaria in international seafarers to be between 500 and 1000 each year. The disease was found to be contracted onboard or in ports.
Hansen et al showed in a longitudinal study from Denmark of 24.132 seafarers employed between 1986 and 1993 that the majority of the 25 malaria cases occurred in connection with trade to West Africa. Irregularity of malaria prophylaxis and chloroquin resistance was assessed to be of importance for risk of infection.
Port health authorities in Croatia reported 23 malaria cases in 19 sailors and 4 tourists on merchant ships arriving in Croatia between 1990 and 1993 (attack rate 0.3% (23/ 8379).
Over 100 cases of malaria were reported to authorities in Japan between 1990 and 1997. It was estimated that approximately 5% of imported cases to Japan concerned seafarers.
In Klaipeda, Lithuania, malaria cases were registered from1973 to 1998. 99 of 113 cases occurred in seafarers and fishermen. In Italy, seafarers and airline personnel represented 21% all registered malaria cases.
Though, by the nature of their job, seafarers cannot avoid exposure to malaria there are well studied preventative measures that greatly reduces the risks of severe disease and death in sailors. The mainstay of prevention in ships sailing to malarious areas is chemoprevention (of note: there is by now no vaccination against Malaria).
The International Medical Guide for Ships requires ships to carry the appropriate drugs as recommended by the World Health Organization or national guidelines for that specific region.
Before travel updated recommendations on the appropriate prophylaxis must be reviewed:
It will be in the responsibility of the ship owner to supply the appropriate drugs to their ships in sufficient amounts. However sailors often fail to use chemoprevention even if available on board, the ship master needs to to promote and facilitate the use of chemoprevention. . It is well known that many seafarers avoid chemoprophylaxis due to unjustified fears of side-effects, thus necessitating appropriate medical counselling and written information.
All ships deploying to malarious areas must carry effective treatment. Provision of methods to confirm diagnosis by microscope, where staff have the skills to use it, or by using a rapid diagnostic test, is recommended.
Use of Malaria Rapid Diagnostic Test in the Ship Environment
Rapid tests are not currently listed as a component of the ship´s medicine chest in the International Medical Guide for Ships but are increasingly carried on board facilitating decision making in situations when a doctor ashore is not available. The advantage of the Malaria Rapid Diagnostic Tests is that they provide a quick result and their use is readily taught. However, quality and performance of the many commercially available tests vary substantially and procurement must take into account product specifications.
Rapid detection tests have variable ability to detect specific malaria parasite densities and species by their target antigens. Thus, not all rapid detection tests are be appropriate for use in seafarers: Some tests will detect P. falciparum or non-P. falciparum only, some detect both antigens. In some areas of South America P. falciparum parasites do not express a certain antigen. If tests are based on this antigen, their sensitivity to detect p. falciparum from this region will be low (only tests that test pLDH will be effective in detecting P. falciparum in these areas of South America). Also it must be understood that tests are designed to detect infections in populations with different epidemiological situations concerning malaria (endemic versus countries that move towards elimination). Therefore, some tests are designed to detect low – density infections (> 100 to 200 parasites /µl), others are designed for endemic countries and will detect high density infections only (> 2000 or 5000 parasites /µl).
If purchasing a test for the ship environment, care must be taken to choose the appropriate test. Generally spoken, appropriate tests for the shipping environment must be heat resistant if storage in a refrigerator in the ship hospital is not possible at all times, the test must detect parasites at a threshold of 100 to 200 parasites /µl with a high sensitivity and low false-positive rate, detect P. falciparum and non-falciparum and –if used for South-America travel – pLDH Antigen, should be easy to use and have an appropriate shelf-life. WHO entertains a product testing program for commercially available Malaria rapid detection tests that are published on the WHO website, that may guide in the procurement process.
Other limitations of the rapid test are, that they continue to be positive in patients who have recently (within 2 weeks*) been treated with effective ant-malarial medicines. The reason is, that the test detects the antigen and not the parasites itself. Thus in a patient with recurrent or persistent signs and symptoms of malaria within 3 to 14 days* after completing a recommend first line treatment, the rapid test may still be positive even after successful treatment and another cause of symptoms must be considered. But it may also be that the patient is in treatment failure and second line therapy for Malaria must be considered (if patient was compliant with therapy). In a patient who is not recovering on first line therapy for Malaria, only a blood film for malaria parasites will allow to establish the diagnosis of treatment failure. However, if a patient develops symptoms and has a positive rapid test or blood smear for malaria parasites 14* or days or more after initiation of therapy where there has been prior clearance of symptoms, this should be considered a new infection and the patient be treated with the first line drug.
(* remark: HRP2 detecting rapid detection tests will stay positive up to 14 days after anti-malarial treatment, pLDH or Aldolase detecting rapid detection tests for 5 days).
In summary, in a patient traveling to a malarious region who develops typical symptoms of Malaria (not earlier than 6 days, typically 10-14 days or later after entering in a risk area), a positive malaria rapid detection tests establishes the diagnoses. However, due the above named limitations and caveats, empiric full dosage treatment without delay s necessary even if the rapid test is negative or if there are diagnostic facilities available on board at all. Treatment must be started immediately and then the rapid test repeated after 24 hours. If symptoms persist after 3 days or patient deteriorates, further medical care is necessary.
Also, the rapid diagnostic test is not suitable for documentation of claims of a work related disease. Depending on the test system the test must be read 15 to 60 min after the buffer was added. After this time discoloration of the system appears and may result in false positive or false negative readings. Therefore it is recommended to produce a blood slide for documentation as described in the WHO International Medical Guide for Ships (page 269). This is a rather simple procedure that can be performed by a seafarer with minimal training. The air-dried slide then must be labelled and placed in an envelope that preferably must be taped to the patient´s record.
No antimalarial chemo-prophylaxis can provide complete protection, so measures to reduce the risk of mosquito bites are of paramount importance. There are specific measures that must be observed in malarious areas:
- Avoid being outdoors between dusk and dawn
- Wear long-sleeved shirts and trousers when going out at night
- Systematic availability of insect repellent on board
- Air condition should be functioning and used
- Window and door screens should be used, if not available, living quarter doors and windows should be kept closed
- Use a insecticide treated bednet when ashore
- Make anti-mosquito sprays or insecticide dispensers that contain tablets impregnated with pyrethroids available to all cabins at night.
- Indoor residual spraying is recommended only after consultation with a public health/tropical medicine expert who can judge on the epidemiological and entomological data. It should be performed by a professional pest management company
WHO promotes82 the ABCD for Malaria protection. It also applies to seafaring:
Be Aware of the risk, the incubation period, the possibility of delayed onset and main symptoms.
Avoid being Bitten by mosquitoes, especially between dusk and dawn.
Chemoprophylaxis, when appropriate.
Immediately seek Diagnosis and treatment if fever develops one week or more after entering an area where there is a malaria risk. Fever may be delayed for up to 3 months, or occasionally longer.
Dengue Fever and Dengue Haemorrhagic Fever
Dengue fever is an acute febrile viral disease characterized by sudden onset fever for 2-7 days, intense headache, myalgia, arthralgia, retro-orbital pain, anorexia, nausea, vomiting and generalized rash (often not seen in dark-skinned patients). Dengue haemorrhagic fever and Dengue Shock Syndrome is a serious course of the infection characterized by acute febrile illness, haemorrhagic diathesis with abnormal blood clotting and increased vascular permeability causing petechia, echymosis or purpura with a tendency to develop hypovolemic shock. Immediate intravenous fluid therapy and further medical treatment is needed. Dengue Type -1, -2, -3 and -4 viruses are transmitted by infected Aedes mosquitoes in areas where the winter temperature is above10°C.
Incubation time is commonly 4-7 days only. No direct person-to-person transmission occurs.
The infective mosquitoes, Aedes aegypti, are day-biting species, with increased biting activity for 2 hours after sunrise. The past 20 years have seen geographic expansion of epidemic dengue fever and dengue haemorrhagic fever from South East Asia to South Pacific Islands, the Carribean and the Americans. Recent epidemics have occurred in Asia (Cambodia, China, India, Indonesia, Laos, Malaysia, Maldives, Myanmar, New Caledonia, Pakistan, Philippines, Singapore, Sri Lanka, Tahiti, Thailand and Vietnam) and in the Americas (Brazil, Colombia, Cuba, Ecuador, El Salvador, French Guyana, Guatamala, Honduras, Nicaragua, Puerto Rico, Surinam and Venezuela).64 It is rare in African countries. Susceptibility in humans is universal; asymptomatic infection can occur. Recovery with infection from one serotype provides lifelong immunity to that serotype only, but infection with another serotype increases the risk of dengue haemorrhagic fever. Studies have been done on the occurrence of dengue among ill returned travellers. The proportion of febrile returning travellers with Dengue has risen from 2% in 1990 to 16% in 2005. 
No studies or reports were identified on the occurrence of dengue and dengue haemorrhagic fever in seafarers. However medical doctors caring for them must be aware that seafarers -as other frequent travellers are at risk to acquire dengue fever and are at higher risk for more severe disease (dengue haemorrhagic fever and/or dengue shock syndrome), though in the individual seafarer it may be difficult to predict outcome of disease in early stages. Seafarers must be educated on the importance of using insect repellents and protective clothing in affected areas and seek medical care if typical clinical signs occur. Living quarters on ships must be provided with screening. Vaccines are under development but not available as of now.
Chikungunya is a virus which is transmitted to humans by the bite of infected Aedes mosquitoes. It is endemic in many South East Asian countries. It causes febrile diseases with symptoms of chills, headache, nausea, vomiting, joint pain, low back pain and rash. Despite the disease being increasingly recognized as a cause of fever in ill travellers, no reports have been published up till now on seafarers.
Yellow fever is a mosquito-borne disease transmitted by infected Aedes mosquitoes. The flavivirus causes a viral disease. Most cases occur in tropical Africa, Central and South America. Lethality of hospitalized cases is high.A vaccine is available. The yellow fever vaccine is the only vaccination which may be made mandatory by a country under the World Health Organization´s International Health Regulations 2005. Under the regulation a country may designate yellow fever vaccination centres. Many countries require immunization to yellow fever in travellers to, or through, their territory. The vaccine provides immunity after 10 days, There is evidence that it produces lifelong immunity in most immunocompetent persons, however most countries will require revaccination after 10 years. No reports have been published on cases of yellow fever in seafarers since 1990.
West Nile Virus
This virus causes West Nile Fever in humans. In a small proportion (1 in 150) the disease can take a severe course, particularly in the elderly. Birds serve as the primary reservoir for the virus. Transmission of the virus occurs via mosquitoes. Since 1999 the virus has re-emerged in North America and temperate European regions. There is no specific treatment and a vaccine is not available.
One report on an outbreak affecting the crew of a Romanian cargo ship on passing the Suez Canal from Romania to Yokohama, Japan from 1977 exists. No reports of disease in seafarers on or after 1990 were identified.
No reports were identified on other diseases from the zoonotic-environmental cluster known to occur in travellers including Leptospirae, Schistosoma, Sand flies or Helminths.