1.12.1. Diagnosis and reporting system
Animal disease surveillance systems comprise passive and active surveillance. In the passive surveillance system, data are collected when the owner reports to the relevant authorities or the animals showing clinical signs of a disease present themselves in some manner, while the animals are sought, caught and tested in active surveillance. Active surveillance systems, although they provide better data, are more expensive (Dorrell, 2007). The risk-based surveillance concept is gaining importance and can provide a higher benefit-cost ratio with existing or reduced resources (Doherr et al., 2001; Stärk et al., 2006). Like any other diseases, it is expensive and logistically impractical to conduct nation-wide active rabies surveillance. But there is a wide difference in surveillance systems used in developed and developing countries. For example, in the USA, animal rabies surveillance is done based on laboratory diagnosis using standard direct FAT by the 126 state health, agriculture and the university laboratories (Blanton et al., 2010). A targeted enhanced rabies surveillance system is also carried out by the wildlife biologists engaged by the United States Department of Agriculture Wildlife Services to work with oral rabies vaccination programs, and focuses on the following types of samples: strange acting (extremely aggressive or docile) animals
where no human or domestic animal exposure has been reported, road kills, animals found dead in addition to road kills, animals with injuries or lesions indicative of highly aggressive behaviour, and euthanized animals from focal trapping at sites where rabid animals were recently confirmed (Slate et al., 2009). The laboratory-confirmed cases of animal rabies are reported to either the health or agricultural department in all states, which then notify the CDC on a regular (weekly) basis (Blanton et al., 2010). These rabies surveillance data are analysed and published in a summary report each year (Krebs et al., 2005; Blanton et al., 2006a; Blanton et al., 2007; Blanton et al., 2009; Blanton et al., 2010). However, it has been stated that the current surveillance systems are inadequate for the efficient management and evaluation of the large scale wildlife rabies vaccine baiting programs in the US (Blanton et al., 2006b). In order to improve the surveillance system, a GIS-based rabies surveillance database and internet mapping application had been created (RabID) which provides a new resource for the rapid mapping and dissemination of data on animal rabies cases in relation to unaffected, enzootic and baited areas where current rabies interventions are ongoing (Blanton et al., 2006b).
In Europe, rabies cases are confirmed by laboratory tests and the rabies surveillance data are collected electronically in Rabies Bulletin Europe (www.rbe.fli.bund.de) and is published quarterly every year as a summary report (Freuling and Müller, 2010, 2011).
In South America, the Pan American Health Organization (PAHO), established a rabies surveillance information system called ‘The Regional Information System for Epidemiological Surveillance of Rabies in the Americas (SIRVERA)’. The member countries were required to submit the periodic data on human and animal rabies cases to this information system so as to monitor the rabies situation in the region (Belloto, 2004; Belotto et al., 2005).
Canine rabies free countries also have a strict quarantine and regulatory system for the import of dogs and cats from rabies endemic countries. Despite these regulations, imported cases of dog rabies are occasionally recorded in those countries through failure of border controls or ignorance of importation rules, presenting risk of introducing rabies and posing a potential
public health risk (Mailles et al., 2004; Castrodale et al., 2008; Fooks et al., 2008; Mangieri et al., 2008; McQuiston et al., 2008; Johnson et al., 2011a; Johnson et al., 2011b; Mailles et al., 2011). In addition to imported dog rabies, cases of human imported rabies are also reported. A total of 42 human deaths from rabies were reported in Europe, the United States and Japan between 1990 and 2010 (based on clinical literature); all of these victims were assumed to have contracted the rabies infection abroad (Malerczyk et al., 2011). The most common continent of rabies origin was Asia (n=16) and Africa (n=14) and at the country level, the most cases were contracted in India (n = 6), the Philippines (n = 6), and Mexico (n = 5) (Malerczyk et al., 2011).
In contrast, systematic and effective rabies surveillance systems are lacking in the developing countries of Asia and Africa (Cleaveland et al., 2002; Knobel et al., 2005; Ly et al., 2009; Wu et al., 2009b; Sudarshan et al., 2007; Hossain et al., 2011). Most rabies diagnoses in both humans and animals are made based on clinical signs, with the exception of few countries
(Kitala et al., 2000; Cleaveland et al., 2002; Knobel et al., 2005; Sudarshan et al., 2007; Ly et al., 2009; Wu et al., 2009b; Hossain et al., 2011). In developing countries patients may not present to medical facilities for treatment of clinical disease because of the grave prognosis of rabies, and clinical cases are often not reported by local authorities to central authorities
(Cleaveland et al., 2002; Knobel et al., 2005; Sudarshan et al., 2007).
At the global level, the WHO collects rabies data through World Survey of Rabies, which obtains rabies data electronically (called RABNET) and has become accessible through the internet for data consultation and online data entry (www.who.int/rabies/rabnet/en).
However, the information available in this database depends on the accurate and regular data uploading from the WHO member counties. For instance, the WHO’s 1999 World Survey of Rabies (WHO, 1999) reported 1722 human rabies deaths in Asia and Africa (147 in Africa and 1575 in Asia), and the decision tree modelling based approach predicted 55000 deaths (24,000 in Africa and 31,000 in Asia) suggesting that only 3% of human rabies deaths are recorded by central health authorities, which translates into a rate of underreporting of 20 times in Asia and 160 times in Africa (Knobel et al., 2005). In addition, the active rabies surveillance studies in Kenya and Tanzania have revealed that the passive surveillance
programme and the officially recorded figures grossly underestimates the true incidence of human rabies by about 75 to 100 times (Kitala et al., 2000; Cleaveland et al., 2002;Mallawa et al., 2006)
The World Animal Health Organization (OIE) also collects animal rabies data electronically through the World Animal Health Information System (WAHIS)
(http://web.oie.int/wahis/public.php?page=home). Similarly, the information available in this data also depends on the accurate and regular data uploading from the OIE member counties and may grossly underestimate the true figures of animal rabies cases (Kitala et al., 2000; Knobel et al., 2005).
1.12.2. Surveillance of healthy-dog carriers of rabies virus
The intermittent excretion of rabies virus in the saliva of apparently healthy dogs and dogs that have recovered from rabies has been observed in Ethiopia (Fekadu, 1975; Fekadu and Baer, 1980; Fekadu et al., 1981; Fekadu et al., 1982). Rabies virus was also isolated from clinically healthy and previously unvaccinated dogs in Nigeria (Aghomo and Rupprecht, 1990) and in Thailand (Kasempimolporn et al., 2007). The reports of excretion of rabies virus in the saliva of apparently healthy dogs lead to the belief that a “carrier state” for rabies might exist (Warner et al., 1996). Healthy dog-carriers were later described in China, with virus being isolated from the brains of apparently healthy domestic dogs (Tang et al., 2005; Lu et al., 2006; Zhang et al., 2006; Dong et al., 2007; Tao et al., 2009; Wu et al., 2009b). For example, Lu et al (2006) found that the brain tissue specimens from 5 of 283 (1.76%) healthy looking dogs collected from rural areas of 13 cities in Guangxi province tested positive for rabies virus by RT-PCR and virus isolation (Tang et al., 2005; Lu et al., 2006).
Similarly, an infection rate varying from 2.3% to 20% were reported in apparently healthy dogs sampled from regions of high incidence of rabies ( Luo et al., 1995; Ge et al., 2002; Dong et al., 2007; Song et al., 2009; Tao et al., 2009). Further investigation to understand the role of dogs as potential healthy carriers of rabies virus was conducted in China (Zhang et al., 2008a). In their experiment (Zhang et al., 2008a), 153 domestic dogs were collected from a rabies enzootic area and monitored for 6 months. Fifteen dogs tested positive to rabies virus antigen in the saliva by ELISA test, but none of the dogs showed any clinical signs of rabies
during the 6 months observation period. Also none of the saliva samples collected either at the time of acquisition or during the observation period was found to be positive for rabies virus RNA by RT-PCR. The viral antigen or viral RNA were not detected in the brain samples collected at the time of euthanasia (Zhang et al., 2008a). These phenomenon and contention may be explained by the fact that rabies virus has reached the CNS before clinical signs appear in those dogs, rather than the existence of carrier or asymptomatic rabies (Song et al., 2009; Wu et al., 2009b).