With regarding to public health, there are two major zoonoses in which is recommended euthanasia for dogs, rabies and visceral leishmaniasis. There are government agencies responsible for the control of these diseases as the Center for Zoonoses Control (CZC), which develops prophylactic programs such as: anti-rabies vaccination in urban and rural population of pets, public awareness, and monitoring and tracking of cases positive. According to the CZC of São Paulo, despite the human and canine rabies being virtually eradicated in the city, all infected animals should be euthanized after clinical signs such as paralysis. This decision comes by the fact of dog becomes a potential transmitter, there are no available treatment and the neurological disorders caused by the disease are progressive and irreversible, both in man and animals.
In relation to the visceral leishmaniasis, the treatment of canine disease is prohibited in Brazil, with drugs used for humans disease and are not registered in the Ministry of Agriculture, Livestock and Supply; on the grounds of risk of resistance developing for the causing agent of the disease,
The leishmaniasis are represented by a group of diseases with zoonotic character that affects humans and several species of wild and domestic animals. Caused by a protozoan digenetic belonging to
According to estimates by the World Health Organization, the global prevalence of the different clinical forms of the disease, cutaneous and visceral, exceeds 12 million cases with a population of 350 million individuals in areas at risk of contracting the infection (WHO, 2001). The leishmanioses are endemic on five continents, in 88 countries located in tropical and sub-tropical regions. The notification is mandatory only in 32 of 88 countries where the disease is prevalent. Thus, the two million new cases are estimated annually, only 600 thousand are officially notified, which shows a high rate of sub-notification (WHO, 2001). Socio-economic changes and behavioral arising from the globalization process hamper not only the control of the illness but also increase the number of victims. Good examples refer to the process of urbanization course of leishmanioses, a process closely related to rural exodus, unemployment, the expansion of slums, wars, among others.
Parasites belongs to the
Infection occurs when the sand fly female bite the vertebrate, blood feeding and ingests infected macrophages. In the gut of sand flies, these macrophages released de amastigotes, which are rapidly converted into promastigotes which multiply adhered to the peritrophic matrix secreted by cells of the stomach of the insect. After the blood digestion, the peritrophic matrix breaks releasing the promastigotes that colonize different parts of the digestive tube of the vector depending on the species of the parasite. The promastigotes remain anchored to the gut epithelium in the process of binary division. After that, biochemistry changes occur in the parasite surface, called metacyclogenesis. The parasites migrate to the anterior part of the vector alimentary tract. The vertebrate host infection is established when the sand fly female infected bite another vertebrate host and regurgitates the promastigotes in the mammalian skin. On that occasion, it is believed that most parasites are eliminated by lytic action of the complement system and by the action of neutrophils and eosinophils present in inflamed skin (Laurenti et al., 1996). However, some promastigotes that escape to nonspecific defense mechanisms of the host are phagocytized by macrophages in the skin, surviving and multiplying in the parasitophorous vacuoles. After successive binary divisions, the countless parasites cause increased on the pressure inside the macrophage lysing the host cell. The released amastigotes are phagocytized by other macrophages initiating an inflammatory reaction that is responsible for maintaining
2.1. Cutaneous Leishmaniasis (CL)
The pathogenesis of cutaneous leishmaniasis is heavily influenced by two fundamental factors: first, related to the immunogenetic background of the vertebrate host and the second, related to virulence of
The immunopathogenesis of American cutaneous leishmaniasis (ACL) has been regarded one of most interesting features concerning this parasitic protozoal disease in viewing of the complex interaction process between the variety of
2.1.1. Control and prophylaxis of CL
The control of cutaneous leishmaniasis is difficult, since their cycle happens mainly in forests, often extensive, preventing the use of insecticides in large-scale. Deforestation for agriculture and livestock development reduces the endemic areas, but determines the appearance of large number of cases during the process. The use of repellents and musketeers of fine mesh, in some situations it becomes possible, as individual protection to avoid the bite of sand flies. Recent colonization areas near forests, can avoid transmitting intra-and peri-domestic with the construction of houses at a minimum distance of 500 m from the forest, due to the low flight capacity of these vectors. But the ideal solution for control of CL would produce an effective vaccine (Genaro, 2002).
3. Visceral Leishmaniasis (VL)
Visceral leishmaniasis is a widespread chronic infectious illness, characterized by irregular fever, hepatosplenomegaly, lymphadenopathy, anemia with leukopenia, hypergammaglobulinemia with hypoalbuminemia, lost weight, edema and progressive weakness leading to cachexia and, finally, to death if the patient is not subjected to special treatment. The human visceral leishmaniasis can assume a spectral character, which determines different clinical forms, ranging from a silent asymptomaatic or subclinical forms to oligosymptomatic, acute up to the classical form (Figure 3) of the disease (Badaró et al., 1986). American and European visceral leishmaniasis are considered zoonosis, while in India it is considered an anthropozoonosis.
3.1. Geographic distribution of VL
Visceral leishmaniasis occurs in several countries of the Old and New World and it is caused by
3.1.1. Ecology and epidemiology of VL
Visceral leishmaniasis is currently emerging and reemerging diseases, both in rural areas as in urban areas. The World Health Organization estimates a global annual incidence of 500 thousand cases. Although the VL is known even today as a disease typically rural, several urban epidemic outbreaks have been reported, due to the favorable epidemiological conditions, mainly in function of the expansion of slums with high population density that have poor sanitary conditions where individuals and infected dogs from endemic areas are your choice of housing in major cities.
Currently, what call attention is the increase in the number of cases of HIV co-infection, especially in southern Europe. This region of Europe HIV infection occurs in rural and suburban areas where visceral leishmaniasis is endemic. Many of these cases are associated with injection drug due to the habit of some groups of users to share disposable syringes and needles. This type of transmission has expanded to Europe's Nordic countries such as Germany, Finland, Norway, changing the classic epidemiological profile of transmission, without the presence of the insect vector and reservoir dogs.
Another aspect relevant in this context of expansion and urbanization of visceral leishmaniasis in the World and especially in Brazil is the possibility of contracting the disease through blood transfusion. This fact is aggravated since serological diagnosis for visceral leishmaniasis is not yet included in the screening of donors in all countries (Brazilian Health Ministry, 2006).
Two distinct epidemiological cycle of VL is observed, a wild cycle and domestic or per-domestic cycle. In the wild cycle are involved as vector,
3.1.2. Prophylaxis of VL
If the control of visceral leishmaniasis is continuous and well conducted, can produce good results; however to the results obtained are durable, there is a requirement of permanent and effective epidemiological surveillance, otherwise gradually the outbreaks arise avoiding previous work. Since that the epidemiological role of dog is established as domestic reservoir and
The use of euthanasia to the control of canine visceral leishmaniasis began with Adler and Tchernomoretz, 1946 after failing to succeed with human treatment and concluded that the best form to disease control would be the elimination of dog. The program carried out in China (Leng, 1982) was based on a triad: the treatment of positive human cases, use of insecticides (DDT) and disposal of dogs in some locations. Using these methods for the control, the anthroponotic leishmaniasis almost finished and the zoonotic leishmaniasis continued and continues in China. They concluded that the removal of dogs helped in the control of leishmaniasis, but it was only one of the control measures.
The Brazilian program for control of VL advocates the canine serologic surveys, targeting to know canine epidemiological situation of the disease in areas with active transmission or with potential to transmission and at the same time, identify the positive dogs to later disposal. However, there are controversial data concerning to this subject. Some studies showed that there are no significant differences between regions where euthanasia was only used as a control measure, when compared to others in which the dog was not eliminated (Dietze et al., 1997), by the other side another study related the reduction of human VL incidence correlated to dog euthanasia but not exclude the possibility to consider other factors that may influence this relationship (Nunes et al., 2010). The difference is the use of the insecticide that presents good results in the control of leishmaniasis. Another point was emphasized by Braga et al. (1998), the importance of sensitivity and specificity parameters of the diagnostic assay, when evaluating the impact of the dog elimination in front of the employed methodology.
After two decades of attempts to control of VL in Brazil, the number of cases in the country increased sharply and broke into urban areas. The Brazilian program, started more than 40 years, is composed by integrating three measures of public health: the free distribution of specific treatment to human patients, the control of domestic reservoirs and the control of the vector. The control of reservoirs has been done by serological diagnosis of domestic dogs where transmission of
In respect of serologic methods employed in epidemiological investigations with the aim of knowing the prevalence of the disease in endemic areas or with potential for transmission of the VL, the parameters of sensitivity, specificity and predictive values of serological techniques employed are of the extreme importance to avoid erroneous interpretations, with false positive or negative. Although the serology is only an indirect method of measuring the infection, not defining the degree of parasitism, the presence of the disease, or even the potential for transmission that the dog may have to the vector. Decrease the number of false positive results would be very important for the efficiency and reliability of the program, avoiding the elimination of the dogs that do not provide risk in the transmission of infection.
The correlation between the clinical status of the dogs and its infectivity for the vector should also be considered in the discussions for the adoption of measures to the control of VL since Pinelli et al.(1994) observed that asymptomatic and symptomatic animals had severe immune response, quite distinct, favor or not the vector infection. Anyway, it is important to mention the report of Barata et al. (2005) showed infection in the laboratory reared vector which feeding in seropositive dogs from different clinical forms of the disease. Cutaneous parasitism in found in intact skin of dogs naturally infected by
According to the technical report of the Ministry of Health of Brazil (Costa & Vieira, 2001), the program for the disposal of domestic dogs presents the lowest scientific-technical support between the three strategies of control program, and recommends that the systematic serological screening followed by dogs elimination should be suspended. Serological examination was recommended for dogs only from endemic areas who presents suspicious symptoms; however the serological test in eluate of blood on filter paper should be replaced by conventional serology; and that the elimination of dogs should be restricted only to the situations in which the diagnosis of visceral leishmaniasis was confirmed by parasitological exams. In addition, the treatment of dogs with drugs available for the human patients is not recommended, both for inefficiency as a measure of public health due to infectivity of treated dogs to the sand fly as for the risk of developing resistance to long-term medication.
Another point to be considered is that the elimination of the seropositive animals for the control of human VL provides the increase in the dog younger population, which is more susceptible to
The increase in the number of VL cases and transmission of
Rabies is transmitted by an anthropozoonosis deposition of contaminated material and inoculation with the rabies virus by biting, scratching or licking the skin in healthy animals or humans. This infectious agent is a RNA virus of the
This virus is composed of two units in its structure: ribonucleoprotein and viral envelope. There are also five proteins, including the viral envelope glycoprotein, of the most important due to stimulation of the immune system and production of neutralizing antibodies, which are able to confer protection against the disease. The virus affects the central nervous system (CNS) causing encephalitis, leading to around 100% of lethality and the high cost in preventing individuals at risk of illness and death. Despite being a disease studied since antiquity is still a public health problem. All mammals are considered sources of infection and therefore can transmit it to humans. The main animal species evolved in the transmission are: dogs, cats, bats, wild dog, marmosets, foxes, cattle, horses, pigs, goats, among others. Until a few years ago it was considered three transmission cycles (urban, rural, and wild) and is currently included another cycle observed among bats, denominated the air (Figure 5). Rabies is an urban problem in developing countries is characterized by the presence of disease in domestic animals such as pet dogs and cats. Rabies is mainly rural transmitter the hematophagous bat (
The incubation period is variable between different species of mammals. In humans this period can vary from two to ten weeks, on average 30 to 45 days. This variation is justified by the extent of the injury, viral inoculation and the virus strain. The infected animal usually begins transmission before presenting signs and symptoms of this disease. This period is well characterized in dogs and cats beginning two to four days prior to clinical manifestations and death occurring after five days of observation of clinical manifestations of disease.
The rabies virus multiplies in the initial period, at the site of inoculation and then reaches nerve endings. Dissemination occurs by retrograde axonal flow in centripetal movement to reach the CNS. That path remains protected by the sheath of nerves, not by stimulating an immune response. On reaching the CNS can replicate at various locations in the dog and cat, the target region is the hippocampus (Ammon's horn) and dentate gyrus (pyramidal neurons), spinal cord horses and cattle in the cerebellum (Purkinje cells). Only when a large amount of virus is produced stimulates the immune system and spreads to several sites, particularly the salivary glands, can also be found in the eyes, hair follicles and sweat glands.Source: Pasteur Institute –SES/SP
4.1. Signs and symptoms in animals
The clinical condition of the animal is divided in podromic phase, furious rabies, paralytic and atypical. The podromic phase is characterized by a period of one to two days, the animals are uneasy with mild or apparent changes in behavior, dogs and cats, do not answer the call of the owners, have attention deficit, do not feed and can be isolated, seek hideouts. Large animals can move away from the group, not eating and isolate themselves. Passing this stage enter into a framework known as furious anger, where they show aggression, attack other animals that commonly live together and even the owner that are used to entertain. Other changes such as hunting boats and giving imaginary flies bite in the air, wander aimlessly, howling incessantly, unable to drink water by the pharyngeal nerve palsy recurrent, drooling, biting and attacking the cages, make changes as ophthalmic strabismus can also be observed. This phase is marked by aggressiveness and hyperexcitability due to encephalitis. The stage called paralytic rabies is characterized by the development of paralysis, especially in the hind limbs, followed by the jaw and forelimbs. When atypical rabies, characterized by slight changes in the behavior, is observed, there are difficulties to diagnose.
4.2. Signs and symptoms in humans
In humans the clinical picture may be divided into the following phases: neurology podromic, coma and death. The symptoms are nonspecific in early stages such as fever, headache, malaise, anorexia and sore throat. Sensitivity can occur at the site of biting, burning, numbness and itching. Then there are the manifestation in the CNS such as anxiety, restlessness, disorientation, hallucinations and seizures. It is commonly characterized by hydrophobia and spasms of swallowing difficulty, in which the person is thirsty, but cannot drink water. Struggling to swallow the saliva occurs which enhances dehydration. The disease progresses to severe psychomotor agitation, altered by seizures. The patient goes into coma, failure occurs breathe and death within five to eight days after onset of symptoms. Rabies is a notifiable shown.
4.3. Control rabies
The control of rabies in pets (dogs and cats) requires a series of measures such as: periodic vaccination against rabies; keep post vaccination against rabies fixed for the second dose in primed; vaccination of cats, among others; seize animals, keep them with quality of life and vaccinate them against rabies right away or when the redemption will be donated; performing euthanasia ethical method, the dogs that do not fit the above mentioned items; send material for laboratory diagnosis Rabies in quantity and frequency appropriate for observing the behavior of this virus; making epidemiological research in positive cases headed for prophylaxis of exposed persons; performing with focus lock vaccination actions and seizure of stray animals, within 72 hours; promote observation of aggressive dogs and cats for ten days from the date of the accident; stimulate the development of education initiatives and health promotion, using the held responsible.
Rabies is a fatal disease and only the development of the disease will take the animal to death, but euthanasia, conducted in an ethical manner, will alleviate the suffering of this animal is affected because this disease has no treatment in veterinary medicine.
The measure of control with greater relevance to rabies control is population control. This control should be accomplished through the castration of domestic animals, especially those who are wandering the street and placed collected for donation and mainly awareness of people to understand the true meaning of responsible ownership. The criteria of responsible ownership should be widely disseminated mainly in schools, because children will disseminate information to family practice and charge what they learned. The possession charge means: giving attention and affection for the animal; the animal out on the street should be conducted with collar and leash with individual controls and the strength to stop him; offering food and good quality water; bathe regularly; from three months to take the animal to receive the rabies vaccine and implement a booster dose after 30 days; routinely take the animal to the vet; take the animal with two months to vaccine other diseases; keeping the animal in space and where appropriate cannot attack other people or animals; if the animal impairs a person performs his observation for ten days; occur when mating these animals get homes for all puppies and not abandon them.
So we can decrease the use of the method of euthanasia to control and combat rabies
Some reports in Brazil, the USA and other countries approach a satisfactory response to treatment in human patients who had the disease. The research evaluating of the treatment effectiveness associated with awareness, the vast majority of people collaborate to minimize the euthanasia of pets.
From what has been discussed in this chapter with regard to leishmaniasis, we can conclude that euthanasia of dogs as one of the main measures used in the control of human disease has not proven very effective. Even with sacrifice of a high number of animals, the number of human cases has not decreased and the disease has spread even to urban areas. This is because other reservoirs may be involved in the biological cycle of the parasite and also because the very fast replacement of the dogs. It shows the need to establish other policies for control of the disease, associated or not to the euthanasia of dogs, such as vector control. In addition, efforts should be made towards prevention of the dog disease, such as the use of repellents to prevent the sand fly bite, and the development of effective vaccines candidates. Regarding to the rabies, the main control measure, animals vaccination has been shown effective in controlling the zoonosis, and the euthanasia is conducted only for sick animals since the treatment is not recommended.