Neglected zoonotic diseases in Nigeria: role of the public health veterinarian

Zoonotic diseases accounts for about 75% of emerging infectious disease and can be devastating to both human and animal health globally. A subset of zoonotic diseases is referred to as “neglected zoonotic diseases - NZDs” as they mainly affect poor populations who live in close proximity to domestic or wild animals often in areas where access to health and adequate sanitary facilities are not available. Furthermore, underestimation of the burden of NZD has continually led to its further neglect in least developed countries such as Nigeria. Controlling zoonotic infections including NZDs in animals is crucial in reducing human infections. Veterinarians provides an understanding of the epidemiology of infectious diseases in animal population and are therefore integral for the overall reduction in global burden of NZDs worldwide. Due to the current lack of and in some cases weak involvement of Veterinarians in policy issues related to zoonotic diseases, there is need to elucidate their importance in NZDs control in Nigeria. This review therefore summarises the neglected zoonotic diseases so far documented in Nigeria and also highlight the important role of the Veterinarian in their prevention and control within both human and animal population. Important recommendations to strengthen the role of the public health Veterinarian for sustainable control of NZDs were made.


Introduction
Zoonoses are diseases that are naturally transmissible between man and vertebrate animals [1]. About 75% of the new diseases that have affected humans over the past 10 years have been caused by pathogens originating from an animal or from products of animal origin [2]. About 20% of all human morbidity and mortality in the least developed countries of the world are attributable to endemic zoonoses [3][4][5]. With increasing ecological changes which favours development of some vectors of infection; urbanization which has led to increased contact with wildlife, which also constitute a significant reservoir of zoonotic infectious diseases as well as other socio-cultural behaviour such as farming, hunting and tourism further encourages the emergence and re-emergence of zoonotic infectious diseases [6]. A subset of zoonotic infectious diseases is referred to as "neglected zoonotic disease -NZDs". These diseases are termed "neglected" as they mainly affect poor populations who live in close proximity to domestic or wild animals often in areas where health and adequate sanitary conditions are scarce [7]. Reports have shown that these diseases were further neglected due to the fact that their burden is usually concentrated in developing countries, where the majority of effort in recent years has focused on HIV/AIDs, tuberculosis, and malaria as well as ineffective diagnostic capacity and poor health care delivery systems that may result in underestimation of disease burden [8]. The WHO has identified eight diseases as NZD including: anthrax, bovine tuberculosis, brucellosis, cysticercosis, echinococcosis, leishmaniasis, rabies and human African trypanosomiasis [1].
Neglected zoonotic diseases have a dual burden because they can be devastating to both public health and animal health and the most vulnerable people are the millions of poor livestock keepers found globally [9]. Zoonotic disease exhibits clinical signs that mimics malaria, typhoid and HIV/AIDS in humans, leading to incorrect diagnoses and under-reporting hence underestimation of the disease burden [10,11]. Neglected zoonotic diseases such as brucellosis constitutes an important public health problem throughout the world, particularly in the tropics, where its control is restricted by inadequate infrastructure, limited resources and lack of information on its significance and distribution [1]. Welburn et al. (2015), suggests that by targeting the animal reservoir to have optimal health, NZDs may reduce the risk of infection for humans, as well as ultimately leading to improved livelihoods through increased animal productivity [11]. In Nigeria, NZD are currently endemic in the animal population and has been reported across various parts of the country. Moreover, there has been an upsurge in the emergence of zoonotic infection in Nigeria, claiming several lives in recent times. The WHO has identified the need for collaborative effort to combat these important group of diseases. Hence the importance of the public health Veterinarian in their prevention and control cannot be overemphasized. This review would summarise the important zoonoses so far reported in Nigeria and also highlight the important role of the Veterinarian in prevention and control in both human and animal population.

Methods
Literature search was conducted in the Google and PubMed biomedical databases including the each of the 8 NZDs: "Anthrax", "Bovine tuberculosis", "Brucellosis", "Rabies", "Cysticercosis", "Taeiasis", "Leishmaniasis" and "Human African Trypanosomiasis"; "Zoonoses" and "Nigeria" as keywords. We also searched through indexes of AJOL journals that published African research. Upon assessment of publication abstract, articles published in English and with relevant prevalence data on human NZDs from Nigeria were included. The bibliographies of the articles that turned up in the initial search were also used to find other references relevant to NZDs in Nigeria. Articles on animal cases and general information about neglected diseases were also included to provide background on the subject matter.

Current status of knowledge Neglected Zoonoses of Importance in Nigeria
Anthrax: anthrax is an acute, often fatal re-emerging zoonotic infection caused by gram-positive spore-forming bacteria (Bacillus anthracis) in contaminated soil [12]. Its spores live naturally in the soil and are ingested by grazing animals such as cattle, sheep, goats and horses and wild herbivorous animals. The disease is of further importance because it presents a potential bioterrorism risk [13]. West and Central Africa including Benin, Burkina Faso, Ghana, the Niger and Togo have been frequently adversely affected by human and animal anthrax [12]. In animals, the disease is contracted from contaminated pasture and is almost always fatal. Previous studies from eastern Nigeria has reported prevalence rates of 5% and 3.3% in blood samples from cattle and goats slaughtered in an abattoir [14]. A more recent study carried out in a Nigerian abattoir recorded 10.5% seroprevalence rate in livestock [15]. Food animals and their products constitute a potential risk to those persons involved in handling of animal and their products [14]. Human infection occurs via contact or Page number not for citation purposes 3 consumption of infected dead animals or animal products [11].
Globally, there are about 2,000 to 20,000 human anthrax cases occurring annually [16]. About 425 human cases were reported in Nigeria between 1988 and 1995 [17,18]. Depending on the route of exposure, clinical anthrax in humans presents in three distinct forms: cutaneous, gastrointestinal, and pneumonic form [19]. Vaccination using anthrax spore vaccine (Sterne attenuated spore vaccine), which is a non-pathogenic non-encapsulated variant strain of B.
anthracis and is currently the effective method of prevention in animal population [20]. Effort are currently ongoing to develop an effective third generation vaccine for use in humans. Quarantine and containment to prevent movement of potentially infected animals or animal products, disposal of carcasses of affected animals by incineration and deep burial as well as use of disinfectant to treat contaminated soil [12]. is considered to be caused by bovine tuberculosis [28]. Human infection occurs as a result of ingesting contaminated unpasteurized milk and raw meat and also by inhaling aerosol from infected livestock [29]. Human disease is characterized by the formation of granulomas (tubercles) in tissues and organs more significantly in lungs, lymph nodes, intestine, liver and kidneys [30]. Detection of bovine tuberculosis in Nigeria is carried out most commonly on the basis of tuberculin skin testing, abattoir meat inspection and rarely bacteriological techniques [31]. Antimicrobial treatment has been attempted in some species, but the treatment must be long term, and clinical improvement can occur without bacteriological cure. The risk of shedding organisms, hazards to humans and potential for drug resistance make treatment controversial. It is recommended that cattle with BTB should not be treated and as such farm animals with tuberculosis must be culled [32]. A human vaccine -Bacillus Calmette-Guérin (BCG) is widely available for prevention of the disease in humans of which M. bovis is the ancestor [33].
Brucellosis: brucellosis, caused by Brucella species, is considered an important neglected zoonosis by the WHO largely due to lack of public awareness and one of the most important endemic zoonotic infections, especially in pastoral and mixed crop-livestock farming systems in Africa [34][35][36]. It is the most common bacterial zoonosis affecting cattle, sheep, goats, pigs, and other animals worldwide, leading to reproductive problems such as abortion, infertility, and low milk yields, death from acute metritis, sterility, arthritis or bursitis (hygroma), and increased cost of animal replacement as well as lowered sale value of infected animals and loss in international trade [37]. There are also indirect economic losses for countries due to control and eradication of brucellosis [38]. Globally, about 500,000 new cases is reported annually, with prevalence rates in some countries exceeding 10 cases per 100,000 population [39]. Several studies have been carried out on bovine brucellosis in Nigeria with varying prevalence rates [40][41][42]. Brucella infections in humans can be contracted either directly or indirectly from exposure to infected animals and animal by-products or consumption of unpasteurized dairy products [43]. Brucellae organisms are shed in large numbers in the milk, urine, blood, and cystic products of infected animals [44].
Direct contact with animals or their secretions through cuts and abrasions in the skin, by way of infected aerosols inhaled or inoculated into the conjunctival sac of the eyes, or via the ingestion of unpasteurized infected milk and dairy products [45]. Symptoms of brucellosis in humans can be highly variable, ranging from nonspecific, flu-like symptoms (acute form) to undulant fever, headache, malaise, night sweats, arthritis and arthralgia, etc [45]. Brucellosis also constitute an occupational risk for farmers, animal handlers, nomads, veterinarians, butchers, abattoir workers, animal products consumer and laboratory personnel [46,47]. A study carried out among abattoir workers in Nigeria revealed a very high seroprevalence rate of 24.1% [48]. Incidence of human brucellosis with varying prevalence have also been reported in other parts of Africa including Tanzania [49]; Chad [50]. Calves should be vaccinated using the Brucella abortus strain 19 (S19) attenuated vaccine. Other management measures that involves proper disposal of aborted material, isolation and treatment of infected animals and routine testing will reduce burden of the disease in animal population thus Page number not for citation purposes 4 prevents human infection. Human at high risk such as abattoir workers should be use personal protective equipment while handling meat products.

Cysticercosis (taeniasis): this is a zoonotic helminth infection caused by tapeworm Taenia solium and is widespread in Africa.
Cysticercosis imposes substantial global burden on human beings related to epilepsy, ocular disorders, other neurological manifestations, and economic losses related to disability and lost productivity [51]. A study by Biu and Ijudai (2012) in pigs reported a porcine cysticercosis prevalence of 9.5% in Northern Nigeria [52].
However, a higher prevalence of porcine cysticercosis based on a detailed abattoir examination of pig carcases was observed in another study carried out in Nigeria with up to 20.5% of pigs infected [53].
Human cysticercosis is acquired from the ingestion of food contaminated with ova of T. solium, with subsequent development of cyst in human tissue [54]. Between 1992 and 1995, two patients suffering from CL died in Nigeria due to lack of timely access to antimonials [84].
Rabies: rabies remains a major concern globally [85]. It is a fatal zoonotic disease caused by a rabies virus of the genus Lyssavirus, family Rhabdoviridae and order Mononegavirales [86]. Humans get infected following bites of an infected animal or contact with saliva of an infected animal from where it migrates to the brain. It has been classified as the eleventh killer disease of the world, killing 60 -100, 000 human beings annually mainly in Africa and Asia. It is recommended that in order to prevent rabies in endemic regions, effective and efficient vaccination of a minimum of 70% of the dog population in a target area should be carried out [87]. Mass vaccination of the animal reservoirs is the cost-effective method of prevention as because post-exposure prophylaxis in humans is much costlier [88]. The cost of rabies is substantial as according to the WHO, about 15 million people received post-exposure prophylaxis annually [89]. Rabies is well known by the indigenous people based on the availability of various indigenous terms -that the disease had been recognised in Nigeria and known as: ciwon kare (Hausa), ara nikita (Igbo) and digbolugi (Yoruba) [90]. However, the first reported case of rabies in animals was in 1925 while the first human case was in 1912 in Nigeria [91]. Since then, canine rabies is an endemic and widespread from various parts of Nigeria [92]. Six people out of 149 suspected dog bite cases were confirmed to have human rabies in a study carried out recently in Nigeria [93].

Role of the public health veterinarian in neglected zoonotic
disease control: WHO defines veterinary public health as, "The sum of all contributions to the complete physical, mental and social wellbeing of humans through an understanding and application of veterinary medical science" [94]. Veterinary public-health activities are those activities conducted at the human?animal interface; that are required to prevent, control and eliminate suffering and economic loss caused by NZDs in both humans and animals [1]. Veterinary public health is devoted to the application of veterinary skills and knowledge for the protection and improvement of public health [95]. Zoonotic diseases such as elucidated above are not wholly veterinary medical problem but also serious public health concern, therefore rapid detection and control in animal population is important for control of human zoonotic infection. The importance of utilizing One Health approach to successfully manage and control zoonotic diseases has been emphasized [5,11,96]. Thus effective preventive measure should involve a "One Health" multidisciplinary approach such that the disease can be controlled in both human, animal and the environment.
There are several important roles that the Veterinarian is engaged in the area of preventing NZDs and a few but not exhaustive are as follows: Response to emerging and re-emerging zoonotic diseases: according to the WHO, the expertise of a public health veterinarian is essential in the public health infrastructure for efficient preparedness and response to known and unexpected disease problems [94]. foodborne infections to the public [99]. There are Veterinarians specialized pharmacology, toxicology, microbiology and are involved in the production of drugs, vaccines and biological products for human and animal use. Vaccines for NZDs such as those against rabies, brucellosis was effectively utilized to control the diseases in most developed countries due to availability of effective vaccines [99]. What is known about this topic  We know that a sub-set of tropical diseases are neglected zoonoses and affect rural people that come in contact with animals mostly in sub-Saharan African;

Research
 We know that these diseases have been documented in the Nigeria among both people and animal population.

What this study adds
 This review provides a single document bringing together the neglected zoonotic diseases so far documented in Nigeria from literature search;  It also provides a comprehensive detail of the current status of these NZDs with relation to burden and public health impact among Nigerian human and animal population;  It documents as a reference, the very important role of Veterinarians in controlling these NZDs and made important recommendations to strengthen the role of the public health Veterinarian.