Introduction
Rodents are mammals which are characterized by a single pair of continuously growing incisors teeth in each of the upper and lower jaws (Olaseha & Obiako, 2014). They live in a variety of terrestrial habitats, including man-made environments. Rodents are constantly associated with unsanitary habitats, such as sewers and pit latrines and thrive in overcrowded apartments. It has been reported that nearly 4 million rodents are born every day (Mbanong, Nock & Ezealor, 2012).
This high abundance leads to more contact between humans and rodents resulting more than ever to debilitating rodent-borne diseases with the increased density of human population. Rodents are carriers of viral, bacteria and parasitic diseases which they transmit through their ectoparasites, food and water contaminated by rodent or through direct contact with rodent excreta and their bites (Davis, Calvet & Leirs, 2015).
Rodent-borne diseases are currently on the rise and many that have been extinct before are now re-emerging. These include Lassa fever, leptospirosis, Hantavirus , Typhus, plague, among others (Centre for Disease Prevention and Control [CDC], 2015). Rodents have also been linked to spread of emerging diseases like severe acute respiratory syndrome (SARS) in Asia (Lin, Duan, Yi, Ying & Lu, 2014).
Cases of re-emerging rodent-borne diseases are worsening for a greater proportion of people in the world today as a result of the increasing population of rodents in the community through urbanisation and difficulties in providing basic standards for infrastructures (sewage, water, rubbish collection, rat-proof housing) which is fundamentally encouraging conditions for the spread of rodent-borne diseases (Olaseha & Obiako, 2014)
In developing countries such as Nigeria, there is a growing proportion of cases of “Fevers of Unknown Origin”. These are diseases that then can spread from human to human after they have been initially picked up from animals. Plague and Lassa Fever fall into this category.
The involvement of rodents in the transmission of babesiosis, cestodes, trematodes and nematodes has exacerbated the transmission of these parasites. Pathogens transmitted by rodent bite or bites by their ectoparasites are listed among the serious emerging infectious diseases worldwide. These diseases causes serious pains, injuries, loss of appetite, swollen joints, weakness of the body and lastly death (Randolph, Miklisova, Lysy, Roger & Labuda, 2010).
Conceptual framework
According to Mustapha (2015), rodents are an important vector for zoonosis (diseases transmitted from animals to humans), and can act as reservoirs for different diseases which can affect people. Erutase (2016) described rodents as vectors/rodents and are small mammals which live at the expense of man, invade his home, eat his food and damage his properties or commodities. She also added that rodents transmit disease to man. There is growing global concern about communicable diseases, particularly as climate change, urbanisation, and agricultural intensification may cause some zoonoses to spread – emerging in new areas or re-emerging in areas thought to be free of the disease. As the world saw with Lassa fever, new rodent-borne diseases can emerge, and improved transport linkages from rural to urban settlements and international travel can lead to large zoonotic outbreaks when the disease is transmitted from person to person.
The re-emergence of rodent-borne diseases can be as attributed to poor awareness among the general public, health care staff and clinicians. Awareness levels are complicated by the fact that the symptoms of some rodent diseases are similar to other better-known diseases, and through the difficulty in appropriately diagnosing the disease causing agents (Sherwin, 2012).
Holmes and Mateo (2014) classified the re-emergence of rodent-borne diseases occurs in two categories. The first category is contagious diseases; which involves the spread of the disease from human to human after they have been initially picked up from animals. Examples of this include Plague and Lassa Fever. The second category of re-emergence of rodent-borne diseases are those which are generally not contagious. This includes diseases picked up through contaminated food and water and often ultimately through rodent urine or faeces. In some circumstances these diseases can be spread from human to human (failing to wash hands), but they are generally of lower communicability status. These diseases can of course cause large scale outbreaks in communities which make use of common water and food sources which have become contaminated.
Common rodent-borne diseases
According to Harding, Paul and Mendl (2010), rodents carry a wide range of disease-causing organisms, including many species of bacteria, viruses, protozoa and helminths (worms). They also act as vectors or reservoirs for many diseases via their ectoparasites such as fleas, ticks, lice and mites. Some of the most common rodent-borne diseases are:
- Lassa fever
- Salmonellosis
- Leptospirosis
- Weil’s disease
- Rat-bite fever
- Plague
- Hantavirus
- Lassa fever
- Lassa fever
Lassa fever, also known as Lassa hemorrhagic fever (LHF), is a type of viral hemorrhagic fever caused by the Lassa virus. Many of those infected by the virus do not develop symptoms. When symptoms occur they typically include fever, weakness, headaches, vomiting, and muscle pains. Less commonly there may be bleeding from the mouth or gastrointestinal tract. The risk of death once infected is about one percent and frequently occurs within two weeks of the onset of symptoms. Among those who survive about a quarter have deafness which improves over time in about half. The disease is usually initially spread to people via contact with the urine or feces of an infected multimammate rat. Spread can then occur via direct contact between people (Ogbu, Ajuluchukwu & Uneke, 2012).
2. Salmonellosis
Rodents can carry Salmonella bacteria that cause illness in both humans and pets. Infection occurs by consumption of food or water contaminated with rodent faeces. The most common source of infection is by food contaminated with the faeces of farm animals. Symptoms such as diarrhea, fever, vomiting and abdominal cramps occur 12 to 72 hours after infection. Once a person is infected, the disease is easily transmitted to other people through poor hand hygiene and poor sanitation (Niemiee, 2011).
3. Leptospirosis
Leptospirosis is an infection caused by species of Leptospira bacteria. It is caught from the urine of infected animals, which include rodents. Humans can become infected by direct contact with urine or other body fluids (except saliva) of infected rodents or through contact with soil, water or food contaminated with the urine of infected rodents. The bacteria live inside the rodent’s kidneys and are passed out in urine. They can survive for weeks or months in soil or water. The bacteria do not only enter the body through the mouth, they can also enter through the skin, especially if broken by a scratch or cut, and the mucus membranes of the eyes, nose and mouth (Nowak, 2009).
4. Weil’s disease
Weil disease is a more serious form of Leptospirosis which can result in organ failure, internal bleeding and death. Common symptoms of Weil disease include jaundice, swollen ankles, feet or hands, chest pain, headaches, vomiting, seizures and coughing up blood (Dickman & McDonald, 2011).
5. Rat-bite fever
Rat-bite fever is caused by two bacteria Streptobacillus moniliformis and Spirillum minus. In infected rodents the bacteria are present in rat faeces and urine and secretions from the mouth, nose and eyes. It is usually caused by a bite or scratch from an infected rat or other rodents such as mice and squirrels. It can also be caught by handling infected animals and ingesting food or drink contaminated with rodent faeces or urine. Rat-bite fever lead to serious complications such as heart infections, meningitis (brain infection), pneumonia (lung infection) and abscesses in internal organs (Parshad, 2009).
6. Plague
The plague is the classic disease that is linked to rats in the human environment. The disease is caused by the bacteria Yersinia pestis, which cycles between rodents and fleas. Several species of rodents are long-term reservoirs of the plague bacteria. Plague is transmitted by bites from infected fleas, process of handling tissue or fluid of an infected animal and ingesting or breathing in of infected particles (Nowak, 2009).
7. Hantavirus
Many species of rodent carry hantaviruses, especially rats and mice. Different species carry different viruses whose virulence varies but which show similar symptoms of flu-like conditions. Humans can catch the disease through contact with rodent urine, saliva and faeces, by touch, contaminated food or drink, or from breathing in aerosolised particles (Barry, 2010).
Factors responsible for re-emergence of rodent-borne diseases
According to Galef and Laland (2011), the re-emergence of rodent-borne diseases is determined by the presence of rodents in a particular population; since they have the tendency of carrying diseases in their habitation. The presence of rodents in a given area is promoted by different factors which include inadequate standard of living, poor sanitation, overcrowding, and homelessness. This gives rise to pathogens which is most likely to be spread by rodents causing gastrointestinal illnesses such as Salmonella spp and Campylobacter spp.
Kay and Hoekstra (2008) stated that availability of food and harbourage is associated with increased rodents’ populations. Availability of food sources influences the abundance of rodents. Improperly stored or disposed food and organic waste, dishevelled gardens, and presence of domestic animals (e.g. dogs, cats, pets, livestock) in residences, gardens or city blocks are correlated with rodent infestations. Availability of harbourage determines whether a population becomes established. Structures that are easily accessible or abandoned may act as a source of infestation
In the opinion of Albert (2015), accessibility to shelter such as holes/cracks in roofs, walls, ceilings, building foundation, access points near utility lines and sewer systems, and particularly abandoned structures are associated with rodent infestations. This is particularly the case with older-aged housing and aging of community infrastructure such as defective drains. Defects in sewer systems and inadequate sewer baiting also contribute to surface infestations. Presence of soil is a strong predictor of Norway rat populations, since they can create their own harbourage by burrowing. In contrast, black rats are more common in areas with high building density since they are good at scaling vertical structures and creating nests out of artificial materials. Higher housing density is associated with urban rodent infestations likely because the dispersal and colonization of one home can affect surrounding dwellings. Rats are also more likely to disperse successfully over short distances
Harkness and Wagner (2015) also highlighted the factors which contribute to rodent infestations to include:
- Food: Rodents must have a food source to survive. When rodents find a food source, they are likely to build a nest nearby and reproduce. Food sources are found in yards and garages and can lead to a rodent problem. They include garbage, bird seed, peanuts, pet food, dog waste, and fruit and nuts that have fallen to the ground from trees. Eliminating food sources is the best way to prevent rodent activity.
- Hiding places: Rodents like to build their nests in hidden areas under structures and trash piles where they feel safe. A rat will look for a hiding place after it has found a food source nearby
- Water: Rodents need water to survive. Locations with standing water or property near bodies of water are more likely to support rodent’s activity.
Mode of transmission of rodent borne diseases
Myllymake (2007) stated that rodent infestation is always considered dangerous because, they can carry diseases; rats often inhabit sewers and can transmit disease to man who work where there is spirochete which causes a serious form of jaundice. Walker (2010) further noted some diseases associated with rodents as observed by the World Health Organisation [WHO] (2010) to include plaque, lassa fever, marine typhus, leptospirosis, rat bit fever, salmonellosis, trichinosis, tularaemia, etc.
Mulungu (2006) stated that rats are connected with the spread of plaque and other infectious diseases, therefore strict regulations should be enforced to reduce their population. In this regards, every ship from foreign port must hold a valid derating exemption certificate and this certificate is issued, but if rats are present, the ship is fumigated and derating certificate is issued.
The regulation further stressed that there are many types of rats, but only two are strongly connected with plaque. These are rattus rattus and rattus norvigicules. Rat should be prevented from coming into contact with man especially in ports as people cross and recross political boundaries.
Lurz (2010) stated that rodents are reservoir of infections for many diseases. These diseases are spread either through rat bites or man eating food that has been contaminated by rats. Fleas wound also inflicted on people which rat and mice bite when sleeping.
Implications of the re-emergence of rodent-borne diseases
The re-emergence of rodent-borne disease has led to several rodent-borne disease diseases which have caused varying degrees of morbidity and mortality. For example, the re-emergence of lassa fever in Nigeria have led to several deaths in the country (Health and Medical News, 2016).
In the United States, The Centers for Disease Control and Prevention [CDC] (2016) identified the re-emergence of Hantavirus Pulmonary Syndrome which is a deadly disease transmitted by rodents through urine, faeces, or saliva in Louisiana and the south-eastern United States. Humans contracted the disease after inhalation of dried, aerosolized secretions.
Also the re-emergence of Murine typhus, a rickettsial infection caused by
Rickettsia typhi, which is a disease occurring worldwide and is transmitted to humans by rat fleas. In some areas peridomestic cycles involving cats, dogs, opossums and their fleas may exist. Symptoms of the disease often include headache, myalgia and rash and seldom last longer than two weeks. The disease is often mild, but untreated severe cases can be fatal.
The re-emergence of rodent-borne diseases leads to poor health conditions which are manifested in the form of fever, chills, muscle pain, vomiting, headache, rash, organ abscesses, pneumonia, endocarditis, myocarditis, or meningitis occur. More severe cases may experience kidney damage, meningitis, liver failure, respiratory distress or death.
Prevention and control of rodents/ rodent-borne diseases
The economic losses resulting from rats and mice infestation are unquestionable and the numbers of deaths due to rodent-borne diseases are innumerable, therefore there is urgent need for it to be controlled. The focus of all rodent control programmes is to reduce their population and eliminate them from human habitation. These can be achieved through a number of ways.
Nicholas and Hines (2007) pointed out some of the ways by which good management of rodent could be achieved with the aim of attaining a high degree of physical, mental and social well-being of workers. The following prevention and control measures are discussed as follows:
- Rat guards: This is a circular usually used in vessels. Sheet metal shield mostly used in a vessel to control rodent by preventing them from boarding or leaving it.
- Environmental sanitation: This generally include all those measures that are chemically less or predictive. It include keeping of houses in good sanitary condition. It deprives rat/mice from sources of food harbour in the area. This can be achieved through maintenance of drains, wrapping garbage and storing in a rust roof dust with a tight fitting cover. Storing of food stuff 12 – 18 inches off the floor in a closed container, proper disposal of waste, storing of items in a manner that will not provide harbourage of rodent/mice, keeping animal feeds cleaned up and regular cutting of bushes around homes, offices, schools and market place.
- Rat proofing: Rat proofing is the eliminating of all holes to prevent rats from entering residential building and food establishment. A building can be rat proofed, eliminating all openings larger than ½ inch. For rat and ¼ for mice. All doors, windows that do not operate properly or shut securely should be repaired, repair air vents that may not be in sound working order, broken glasses or stones and get them properly cemented.
- Trapping: Another method of controlling rodents is by the use of traps to kill them. Wooden or metal or rat book type of trap are the commonly used in these connection. For success to be achieved, large number of traps must be used at a time. Rats usually avoid source of death if the trap is in one corner of the house. They will it at another site and many of them would be killed in the process, traps must be placed against the well behind bags of flour and already baked bread. Always use new bait daily and trap must be disinfected after each use. If this is not done, the smell of the trap will scare the rodents away.
- Fumigation: The control of rodents by fumigation can be very effective by the use of chemicals, but may be expensive and dangerous. Fumigation is a process of eliminating rodents of public health importance in the ship, store, warehouses, factories or regulated premises, homes by the use of chemical fumigants. Before fumigation is carried out, the fumigator must know the choice of chemical to be used as some of them are more dangerous and harmful to the health of users and some of them have been banned or severely restricted because of evidence harmful effects on human being and the fumigator must how the following.
- The type of infestation, infection and the object of infection.
- Must know the effective agent.
- Must know the rate of infection and the area coverage.
- The concentration of the chemicals.
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