Serological and infection statuses of dogs from a visceral leishmaniasis-endemic area

Abstract

OBJECTIVE This study investigated the serological status of dogs living in a visceral leishmaniasis-endemic area and its correlation with the parasitological condition of the animals.METHODS Canine humoral response was evaluated using the sera of 134 dogs by enzyme-linked immunosorbent assay and immunohistochemistry to detect parasites in the skin, lymph node, and spleen of the animals. The specific antibodies investigated were IgG, IgG1, IgG2, and IgE.RESULTS According to the parasitological, laboratory, and clinical findings, the dogs were placed into one of four groups: asymptomatic with (AP+, n = 21) or without (AP-, n = 36) Leishmania tissue parasitism and symptomatic with (SP+, n = 52) or without (SP-, n = 25) parasitism. Higher IgG and IgE levels were positively correlated with the infection condition and parasite load, but not with the clinical status. In all groups, total IgG was the predominant antibody, which occurred at the expense of IgG2 instead of IgG1. Most of the infected dogs tested positive for IgG (SP+, 98.1%; AP+, 95.2%), whereas this was not observed with IgE (SP+, 80.8%; AP+, 71.2%). The most relevant finding was the high positivity of the uninfected dogs for Leishmania-specific IgG (SP-, 60.0%; AP-, 44.4%), IgE (SP-, 44.0%; AP-, 27.8%), IgG1 (SP-, 28.0%; AP-, 22.2%), and IgG2 antibodies (SP-, 56.0%; AP-, 41.7%).CONCLUSIONS The serological status of dogs, as determined by any class or subclass of antibodies, did not accurately distinguish dogs infected with L. (L.) infantum chagasi from uninfected animals. The inaccuracy of the serological result may impair not only the diagnosis, but also epidemiological investigations and strategies for visceral leishmaniasis control. This complex serological scenario occurring in a visceral leishmaniasis-endemic area highlights the challenges associated with canine diagnosis and points out the difficulties experienced by veterinary clinicians and coordinators of control programs.

Value of the oral swab for the molecular diagnosis of dogs in different stages of infection with Leishmania infantum

“…The canine diagnosis is based on clinical manifestations as well as on laboratorial tests to confirm the disease in dogs suspected to be ill or to investigate infection in apparently healthy dogs (Miró et al, 2008). Serology is by far the most widely used for this purpose, especially in surveys carried out in endemic areas, but it does not fully discriminate dogs infected with L. infantum from those with other diseases (do Rosário et al, 2005;Zanette et al, 2014;Laranjeira et al, 2014;Laurenti et al, 2014), as it fails to detect a portion of animals with subclinical infection (Porrozzi et al, 2007), and dogs vaccinated against leishmaniasis from those naturally infected (Marcondes et al, 2013). The insufficient accuracy of serological assays has caused the euthanasia of false-positive animals and, conversely, the maintenance of false-negative dogs in transmission areas, increasing risk to humans by the transmission route dog-sand fly-human (Bevilacqua and Alves, 2004;Laurenti et al, 2013).…”

Cutaneous parasitism in patients with American visceral leishmaniasis in an endemic area

“…Visceral Leishmaniasis (VL) is an endemic disease undergoing geographical expansion and represents a public health concern in many regions of the world 1 . In Asia and East Africa, VL is caused by Leishmania donovani, while in the American continent and Southwestern Europe the main infectious agent is L. infantum.…”

“…The main vector for L. infantum in the American continent is Lutzomyia longipalpis 3 , a sandfly species. In urban areas, the domestic dog is considered to be the main source of infection for the vector 1 , and as far as we know, little has been published on interhuman transmission in Brazil 4,5,6,7 .…”

“…Programs focusing on disease control usually include vector control, culling sick dogs and early treatment of affected humans 1 . However, the elimination of infected dogs has been ineffective 3,8 suggesting that other competent reservoirs of L.infantum 5…”

Visceral leishmaniasis in Brazil: rationale and concerns related to reservoir control

“…An article on this issue of Revista de Saúde Públi ca 11 emphasizes an important and often overlooked problem with the strategy of culling seropositive dogs: the high proportion of uninfected dogs that test positive for Leishmania-specific IgG antibodies. The substandard specificity of tests used for identifying infected dogs in the field lead to the sacrifice of many false-positive dogs, particularly when the prevalence of infection in the dog population is low.…”