Toxoplasmosis outbreak in a private collection of squirrel monkeys (Saimiri sciureus) in Cuernavaca, Morelos, Mexico

Abstract

Toxoplasmosis is a disease of worldwide distribution that parasites the intestinal tract of wild and domestic cats. However, in New World monkeys it is considered an acute and fatal illness. The reason for its high susceptibiliy in this particular species is still unknown, but it has been theorized that their habitat and living conditions, in high trees, might be an important factor. Necropsy was performed on 5 squirrel monkeys (Saimiri sciureus), three males (adult) and two females (one of them gravid), with a clinical history of eye redenning and presence of bloody serous foam in the nostrils. Gross examination of the lung showed non collapsed lobes, dark red parenchyma and irregular pale pink nodular areas. All five animals showed apparent hepatomegaly. Histological findings revealed an interstitial pneumonia with a prominent thickening of alveolar septae, and numerous foamy macrophages with intracytoplasmic basophilic structures 20- 25 μm long, covered by a refringent wall and housing PAS positive basophilic structures that were aproximately 8 μm long (bradyzoites), which were identified as protozoal cysts. The liver showed multiple foci of periportal inflammatory cells and numerous parasitic cysts that were also observed in spleen and brain tissue. Inmunohistochemical technique was performed on selected samples of brain, liver and lung tissue, which resulted positive for Toxoplasma gondii using antibodies of hyperimmune antiserum-caprine 6244 origin, in a 1:300 dilution. Samples of the same tissues were processed for transmission electron microscopy. Hepatocytes of the liver showed multiple intracytoplasmic vacuoles with parasitic structures consistent with tachyzoites, which were 3.6 μm long and measured 2.3 μm in diameter. They possesed a slightly wavy electrodense plasmatic membrane that exhibited a conoid in its anterior end, along with several electrodense micronemes. Ultraestructural features like the conoid and the location of micronemes allowed us to identify the parasite as Toxoplasma gondii. Clinical history, necropsy findings, microscopic examination, inmunohistochemical analysis and electron microscopy of all five squirrel monkeys were consistent with a diagnosis of systemic toxoplasmosis. This report shows the high suceptibiliity of New World monkeys to become infected with this parasite. Therefore, toxoplasmosis should be considered among the differential diagnosis for diseases with non specific clinical signs in this particular species.