Laboratory animals are essential mainly for experiments aiming to study pathogenesis and evaluate antivirals and vaccines against emerging human infectious diseases. Preclinical studies of coronavirus disease 19 (COVID-19) pathogenesis have used several animal species as models: transgenic human ACE2 mice (K18 mice), inbred BALB/c or C57BL/6N mice, ferrets, minks, domestic cats and dogs, hamsters, and macaques. However, the choice of an animal model relies on several limitations. Besides the host susceptibility, the researcher’s experience with animal model management and the correct interpretation of clinical and laboratory records are crucial to succeed in preclinical translational research. Here, we summarise pathological and clinical findings correlated with virological data and immunological changes observed from severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) experimental infections using different well-established SARS-CoV-2 animal model species. This essay aims to critically evaluate the current state of animal model translation to clinical data, as described in the human SARS-CoV-2 infection.

This study was conducted to analyse the course and the outcome of the liver disease in the co-infected animals in order to evaluate a possible synergic effect of human parvovirus B19 (B19V) and hepatitis A virus (HAV) co-infection. Nine adult cynomolgus monkeys were inoculated with serum obtained from a fatal case of B19V infection and/or a faecal suspension of acute HAV. The presence of specific antibodies to HAV and B19V, liver enzyme levels, viraemia, haematological changes, and necroinflammatory liver lesions were used for monitoring the infections. Seroconversion was confirmed in all infected groups. A similar pattern of B19V infection to human disease was observed, which was characterised by high and persistent viraemia in association with reticulocytopenia and mild to moderate anaemia during the period of investigation (59 days). Additionally, the intranuclear inclusion bodies were observed in pro-erythroblast cell from an infected cynomolgus and B19V Ag in hepatocytes. The erythroid hypoplasia and decrease in lymphocyte counts were more evident in the co-infected group. The present results demonstrated, for the first time, the susceptibility of cynomolgus to B19V infection, but it did not show a worsening of liver histopathology in the co-infected group.

Uma das principais propriedades a serem estabelecidas para o desenvolvimento de vacinas seguras e atenuadas de flavivirus,é a taxa de replicação viral. Neste trabalho, aplicamos a metodologia de amplificação pela reação em cadeia da polimerase em tempo real e titulação viral por plaqueamento para determinação da replicação do vírus 17DD (FA 17DD) e recombinantes, expressando proteínas do envelope de dengue sorotipos 2 e 4 (17D-DENV-2 e 17D-DENV-4). As amostras de soros de macacos inoculados por via intracerebral ou subcutânea com FA 17DD ou 17D-DENV foram usadas para determinar e comparar a viremia induzida por estes vírus. A quantificação da carga viral em amostras de macacos inoculados por ambas as vias com FA 17DD sugere restrita capacidade de replicação com taxa não superior a 2,0 log10 PFU mL-1 ou 3,29 log10 cópias/mL-1. Os vírus recombinantes 17D-DENV mostraram-se tão atenuados quanto o vírus 17DD, tanto porRT-PCR em tempo real quanto por plaqueamento, com título médio máximo de 1,97 log10 PFU mL-1 ou 3,53 log10 cópias/mL-1. Estes dados servem como base comparativapara caracterização de outros vírus vivos atenuados, derivados do vírus 17D, candidatos a vacinas contra outras doenças.

For the development of safe live attenuated flavivirus vaccines one of the main properties to be established is viral replication. We have used real-time reverse transcriptase-polymerase chain reaction and virus titration by plaque assay to determine the replication of yellow fever 17DD virus (YFV 17DD) and recombinant yellow fever 17D viruses expressing envelope proteins of dengue virus serotypes 2 and 4 (17D-DENV-2 and 17D-DENV-4). Serum samples from rhesus monkeys inoculated with YFV 17DD and 17D-DENV chimeras by intracerebral or subcutaneous route were used to determine and compare the viremia induced by these viruses. Viral load quantification in samples from monkeys inoculated by either route with YFV 17DD virus suggested a restricted capability of the virus to replicate reaching not more than 2.0 log10 PFU mL-1 or 3.29 log10 copies mL-1. Recombinant 17D-dengue viruses were shown by plaquing and real-time PCR to be as attenuated as YF 17DD virus with the highest mean peak titer of 1.97 log10 PFU mL-1 or 3.53 log10 copies mL-1. These data serve as a comparative basis for the characterization of other 17D-based live attenuated candidate vaccines against other diseases.

Achados de necropsia em três casos de toxoplasmose ocorridos naturalmente em macacos-de-cheiro (Saimiri sciureus) obtidos de capturas na região Amazônica foram descritos. A avaliação histopatológica do fígado, baço, rins e linfonodos mesentéricos mostrou múltiplos focos de inflamação e necrose. Cistos morfológicos típicos e bem definidos de Toxoplasma gondii e formas livres foram detectados pelo método da imunoperoxidase com infiltrados inflamatórios. A presença de T. gondii na colônia de primatas estudada pode influenciar severamente os resultados de experimentos realizados nos animais.

Necropsy findings in three cases of naturally occurring toxoplasmosis in squirrel monkeys (Saimiri sciureus) obtained as wild catches from the Amazon region were described. Histopathological evaluation of the liver, spleen, kidneys and mesenteric lymph nodes showed multiple foci of inflammation and necrosis. Typical, well-defined morphologic Toxoplasma gondii cysts and free forms of the parasite were found by immunoperoxidase staining within inflammatory infiltrates. The presence of T. gondii in the studied colony could severely influence the results of experiments performed in the animals.

Foram evidenciadas lesões histológicas nos pulmões de macacos rhesus (Macaca mulatta) relacionadas ao Pneumonyssus simicola. As principais alterações incluíram numerosos cistos variando de 1-5 mm de diâmetro, com paredes finas e amplamente distribuídos nos pulmões; bronquiolite e peribronquiolite, onde os ácaros foram encontrados associados com materiais particulados pigmentados ou não. Nosso estudo incluiu dados de 347 macacos rhesus submetidos a necropsias no decorrer de 20 anos. A acaríase pulmonar foi diagnosticada em quatro animais adultos debilitados, o que representou uma incidência muito baixa do parasita (1,2%) na colônia. A literatura descreve uma alta incidência de acaríase pulmonar em macacos do Velho Mundo. O presente estudo confirma a ubiqüidade do P. simicola em macacos rhesus nascidos e manejados em cativeiro, que compromete sua utilização em estudos experimentais envolvendo o sistema respiratório.

Histological lesions in the lungs of rhesus monkeys (Macaca mulatta) related with Pneumonyssus simicola were evidenced. The most prominent pathologic alterations included numerous thin-walled cysts 1-5 mm diameter scattered throughout the lungs, bronchiolitis, peribronchiolitis where the mites were found associated with pigmented and non-pigmented materials. Our study included data from 347 rhesus monkeys submitted to necropsies during 20 years. Four adult debilitated animals were found with pulmonary acariasis which showed a very low incidence of parasite (1.2%) in the colony. Most of the published literature described as common and widespread pulmonary acariasis in Old World monkeys. The present study confirms the ubiquity of P. simicola in captive born and raised rhesus monkeys that would compromise experimental studies involving the respiratory system.

Philander frenata e Didelphis marsupialis mantém Trypanosoma cruzi sem desenvolver aparentemente nenhuma doença. Ao contrário de Didelphis marsupialis, Philander frenata mantém subpopulações do grupo T. cruzi II. Aqui, nós comparamos a resposta imune humoral de dois didelfídeos natural e experimentalmente infectados com o grupo T. cruzi II, empregando as técnicas de SDS-PAGE/Western blot e por um método de imunofluorescência indireta. Também estudamos os padrões histopatológicos de P. frenata infectado natural e experimentalmente por T. cruzi. O soro de P. frenata reconheceu mais antígenos que o de D. marsupialis. Polipeptídeos de 66 e 90kDa foram os antígenos mais reconhecidos por ambas espécies nas frações enriquecidas de membranas solúveis. P. frenata reconheceu intensamente o antígeno de 45kDa. Nossos resultados indicam que: não existem diferenças quantitativas e qualitativas nas fases subpatente e patente no padrão de reconhecimento de P. frenata; as diferenças no padrão de reconhecimento de antígenos de parasitas pelos soros de P. frenata e D. marsupialis sugerem que provavelmente essas espécies "aprenderam" a viver em harmonia com T. cruzi por estratégias distintas; embora P. frenata não apresente doença aparente, lesões tissulares tendem a ser mais severas do que as descritas para D. marsupialis; ambos didelfídeos provavelmente adquiriram a infecção por T. cruzi depois de sua divergência evolucionária.

Philander frenata and Didelphis marsupialis harbor parasitism by Trypanosoma cruzi without developing any apparent disease and on the contrary to D. marsupialis, P. frenata maintains parasitism by T. cruzi II subpopulations. Here we compared the humoral immune response of the two didelphids naturally and experimentally infected with T. cruzi II group, employing SDS-PAGE/Western blot techniques and by an Indirect immunofluorescence assay. We also studied the histopathological pattern of naturally and experimentally infected P. frenata with T. cruzi. P. frenata sera recognized more antigens than D. marsupialis, and the recognition pattern did not show any change over the course of the follow up of both didelphid species. Polypeptides of 66 and 90kDa were the most prominent antigens recognized by both species in the soluble and enriched membrane fractions. P. frenata recognized intensely also a 45kDa antigen. Our findings indicate that: 1) there were no quantitative or qualitative differences in the patent or subpatent phases in the recognition pattern of P. frenata; 2) the significant differences in the recognition pattern of parasitic antigens by P. frenata and D. marsupialis sera suggest that they probably "learned" to live in harmony with T. cruzi by different strategies; 3) although P. frenata do not display apparent disease, tissular lesions tended to be more severe than has been described in D. marsupialis; and 4) Both didelphids probably acquired infection by T. cruzi after their evolutionary divergence.

The infection pattern in Swiss mice and Triatomine bugs (Rhodnius neglectus) of eleven clones and the original stock of a Trypanosoma cruzi isolate, derived from a naturally infected Didelphis marsupialis, were biochemically and biologically characterized. The clones and the original isolate were in the same zymodeme (Z1) except that two clones were found to be in zymodeme 2 when tested with G6PDH. Although infective, neither the original isolate nor the clones were highly virulent for the mice and lesions were only observed in mice infected with the original stock and one of the clones (F8). All clones and the original isolate infected bugs well while only the original isolate and clones E2 and F3 yielded high metacyclogenesis rates. An observed correlation between absence of lesions in the mammal host and high metacyclogenesis rates in the invertebrate host suggest a evolutionary trade off i.e. a fitness increase in one trait which is accompanied by a fitness reduction in a different one. Our results suggest that in a species as heterogeneous as T. cruzi, a cooperation effect among the subpopulations should be considered.