Ships carry not only passengers and their luggage, vehicles and their loads, but may carry unwanted organisms such as flies, cockroaches, mosquitoes, fleas, and even other pests. These injurious organisms may enter a ship either directly from the ship's open spaces including ramps, portholes, or hawsers, they may be carried in food supplies, cargos, luggage, and vehicles, or may be carried on humans or animals as ectoparasites.

Vectors on board ships can cause harm in different ways. They may cause illness on board ships, and this may happen through the consumption of food containing human enteropathogens, mechanically transmitted by flies or cockroaches. Stored food products aboard ships may be damaged or contaminated by live or dead insects, faeces, odours, webbing or cast skins. Furthermore, vectors such as mosquitoes may be introduced, and established in areas in which they have not previously been found [1, 2] and where vector borne diseases can spread. There are at least five reported cases of port malaria among people who had no recent travels or blood transfusions, but worked or lived close to harbours in Italy, France, Belgium and Israel [3–6]

Ferries serve as a means of transport on regular itineraries from one place to another and are becoming an increasingly popular form of travel in Greece. Among the EU ports, Piraeus registered an increase (+3.4%) of the number of passengers traveled in 2005 comparing with the previous year.{Amerini, 2007 312/id}. About 30 million passengers and 7 million vehicles are carried by ferries in Greece annually.

Ferries provide conditions suitable for the survival and growth of insect populations. Even though they are not the natural habitat conditions for many arthropod species, there are a variety of harborage areas and when sanitation measures are not adequately taken food sources are available for many synanthropic insects such as flies, cockroaches and ants. Inaccessible spaces including behind and below equipment, in voids and ducting, and even between bulkheads and deckheads, are difficult in treatment once infested. In addition, standing water at different areas of the ship open spaces like lifeboat covers, bilges, scuppers, awnings, gutters, and air treatment plants can hold insect larvae.

Closed living accommodation favour the spread of ectoparasites from one person to another. Historically, typhus fever was one of the diseases responsible for the high death rate among the crowded prison ships in the New York harbour during the American Revolution. Overcrowding, bad hygiene and lack of ventilation made a ship an ideal environment for typhus, which was passed on by lice [8]. In recent years, scabies outbreaks, a disease caused by mites, have been reported on board cruise ships (personal communication, EU SHIPSAN project Partnership, September 2007).

Various itineraries in ports of different countries, where no vector control measures are applied may increase the possibility of ship infestations. To our knowledge no studies exist on the examination of port itineraries in relation to ship infestation. Port areas are of high risk for infestations as, a large number of different types of ships arrive, load or unload cargoes originating from all over the world. In addition, great quantities of food are transferred and stored in storage areas of ports, while containers stacked in docks provide harbourage places for pests.

Although there are many published studies describing pest infestations of land-based establishments such as hospitals and restaurants [9–12], few data exist for the presence of arthropods and rodents on board passenger ships in resent years. The aim of this study was: a) to survey ferries for the presence of rodents and arthropods of public health importance, b) to identify ship locations which facilitate pest infestations, and c) to evaluate the implemented pest control programs.

Our study confirms the presence of different pests of public health importance on board ferries. The house fly was the most commonly found insect on board (85.7% of the ships), even though ferry galleys are mechanically ventilated and the open spaces where flies can enter a ship are limited. The second most frequently noted pest was the cockroach. Both synanthropic insects can significantly contribute to the spread of food-born protozoan diseases [13]. Cockroaches have been recognized as a major cause of asthma morbidity and several cockroach-produced allergens have been identified and characterized [14]. A study carried out in Hamburg, Germany, indicated that cockroach sensitized seamen often showed the symptoms of obstructive lung function impairment, which is evidence for an occupational respiratory risk due to the shipboard exposure to cockroaches {Oldenburg, 2006 616/id}. Inspection reports posted on the US Centers for Disease Control and Prevention, Vessel Sanitation Program website often include violations concerning the presence of cockroaches, drain flies, house flies and fruit flies aboard cruse ships [16].

Our study suggests that about 50% of the 21 ferries surveyed were infested with Blattella germanica and the majority of them had not great infestation. One ship was found to be highly infested; another 4 ships were moderately infested, while 6 ships had low infestation. The majority of the cockroaches collected were nymphs. This probably indicates that the adult population was eradicated through the application of pesticides, but nymphs were able to survive in their harbourage areas, where pesticides are difficult to apply.

The absence of Salmonella spp. from the cockroaches tested does not exclude the presence of other enteropathogens. Other studies carried out in different land based establishments have shown that various pathogenic organisms have been isolated from cockroaches' cuticle or gut [17, 18].

In order to collect information on pest species which can be found on board ships generally, we used complaints data from the archives of Public Health Authorities. This was used to have an indication of the pest species and not to make any conclusions about the nuisance caused by them or the frequency of their presence and the size of their population on board. Very few people will complain about mosquitoes or other biting insects, but they may be on board and a public health threat to passengers and new areas.

No rodents were captured aboard the 21 ferries during the survey. It is possible that one old ferry was rodent-infested during the study, due to the presence of a trap which was placed in the galley by the crew members. According to the information collected through the interviews and the review of the Port Health Authorities archives, it seems that rodents can be found only occasionally on board, since over the past 10 years, only one complaint was reported by passengers and one sighting by a crew member.

There are few studies that report the extent of rodent infestations still occurring on ships. These studies that have been published, report upon merchant ships. Findings of surveys carried out by the Government of China Import and Export Inspection and Quarantine Department Bureau indicated that from 1990 to 1998, 24.7% of the 1093 incoming ships examined were infested with rodents [19]. Another study carried out in the Shimizu port, Japan reported that 47 rats captured aboard vessels. Genetic studies of the ship rats showed that they were different from the rat populations in the harbor [19].

Three ferries were infested with bedbugs. It is possible that bedbugs were transported in luggage or in bedding that were carried onto ships by passengers. The ferry environment provides areas suitable for bedbug harbourage: in cracks and crevices in furniture and walls, in upholstered furniture, and in mattress seams. The presence of bedbugs has increased dramatically in hotels and motels and on cruise ships, as well as in college dorms and nursing homes, over the last five to 10 years [20]. Furthermore, the incidence of skin disease secondary to infestation with the human bedbug, Cimex lectularius, has increased dramatically in the United States and in the United Kingdom [21]. Extermination of bedbugs using cleaning techniques and pesticides is necessary to prevent recurrence [22].

We report an isolated incidence of flea infestation in one ferry. Flea control is justified by the direct and indirect pathogenic roles of fleas (transmission of plague, tularaemia, myxomatosis, Dipylidium caninum) [23]. Since fleas are ectoparasites of dogs and cats, it is important to point out that those pets should be transported in specific ship locations especially designed for that purpose, while health certificates should be held.

Unfortunately, we were not able to study possible invasions of species found aboard ships to the destinations. This required knowing the species that are native or not in many different regions in Greece, but there are not enough data available for all these regions. It is possible that most of the species found such as German cockroaches, house flies, fleas and bedbugs are just being transported between regions where they are native already.

Ship itineraries did not show any association with ship infestations. This would be unlikely to happen because many ferries had the same destinations and similar itineraries, while the frequency of travel did not differ among them.

Our findings suggest that pest control programs should focus on different ship locations depending on the pest species. Cockroach and fly control measures should focus on galleys, especially refrigerators and other electrical appliances, and places where food is stored or handled including dining rooms, bars, pantries, garbage rooms and food storage rooms. Both cabins and lounges can be infested with bedbugs. The presence of other pests such as ants, beetles, butterflies, and spiders in the garage of the ferries indicates that different pests can have access to ships when in ports, through open ramps. Control measures should be taken on a regular basis, in order to prevent rats entering the ships. Examples of such measures include placement of rat guards in hawsers, closure of ramps when they are not in use, lighting of the ships' open spaces during the night, and installation of self-closing doors.

Our study indicates that older ships had increased cockroach infestations, and therefore pest control programs should be more persistent and should be applied on older ships more frequently. The application of an integrated pest control program is more effective when including record monitoring. Ferries implemented hazard analysis within their operations to ensure food safety presented less cockroach infestations. The legislation of HACCP and its application in ship galleys may contribute to the reduction of cockroach infestations. The occasional application of pesticide sprays for domestic use by crew members is not effective for cockroach control.

Even thought two pesticides were positively associated with cockroach infestations, we cannot draw any conclusions on their effectiveness. We were not able to evaluate the method of application of these pesticides (locations and frequency of application etc), or to examine other factors such as pesticide resistance.

The revised International Health Regulations (2005) is the global community's new legal framework against acute public health risks that can spread internationally. The importance of vector borne diseases transmission through ships on international voyages has been recognized under these Regulations, and provisions for vector borne diseases control have been included regarding competent port authorities, ship operators, and designated national authorities. Countries should establish programmes to control vectors at ports where ships on an international voyage arrive of depart [24]. The 2004 draft of the Guide to ship sanitation of the World Health Organization includes aspects regarding design, construction and operational control measures for insects and rodents, as well as rat proof construction. It is intended to be used as a base for the development of national approaches to controlling the hazards on ships, as well as providing a framework for policy making and local decision making. Adherence to the requirements of the revised International Health Regulations (2005) and to guidelines of the WHO Guide to Ship Sanitation is expected to contribute in eliminating the presence of vectors at ports and on board ships.

Different pests of public health importance can be found on board ferries. Integrated pest control programs should involve control measures for a variety of pest species including flies, cockroaches, fleas, bedbugs, ants, and rodents. Early identification of their presence is important to avoid large infestations. Measures for cockroach control should be more persistent in older ships, while different ship locations should be monitored and treated depending on the pest species. HACCP system aids in the prevention of cockroach infestations on board.