Epidemiology and control of neosporosis and Neospora caninum

Abstract

Neospora caninum is a protozoan parasite of animals. Until 1988, it was misidentified as Toxoplasma gondii. Since its first recognition in dogs in 1984 and the description of the new genus and species Neospora caninum in 1988, neosporosis has emerged as a serious disease of cattle and dogs worldwide. Abortions and neonatal mortality are a major problem in livestock operations, and neosporosis is a major cause of abortion in cattle. Although antibodies to N. caninum have been reported, the parasite has not been detected in human tissues. Thus, the zoonotic potential is uncertain. This review is focused mainly on the epidemiology and control of neosporosis in cattle, but worldwide seroprevalences of N. caninum in animals and humans are tabulated. The role of wildlife in the life cycle of N. caninum and strategies for the control of neosporosis in cattle are discussed.

FIG. 1.

Life cycle of Neospora caninum. (Reprinted from reference .)

FIG. 2.

Life cycle stages of Neospora caninum. (A) Impression smear of the liver of an experimentally infected mouse depicting numerous tachyzoites (Giemsa stain). Notice that the tachyzoites vary in dimension, depending on the stage of division: (a) a slender tachyzoite, (b) a tachyzoite before division, and (c) three dividing tachyzoites compared with the size of a red blood cell (arrow). (B) Histological section of a tissue cyst inside a neuron in the spinal cord of a congenitally infected calf (hematoxylin and eosin stain). Note the thick cyst wall (opposing arrowheads) enclosing slender bradyzoites (open triangle). The host cell nucleus (arrow) is cut at an angle. (C) Unsporulated oocyst (arrow) with a central undivided mass in the feces of a dog (unstained). Bar, 10 μm. (D) Sporulated oocyst (arrow) with two internal sporocysts (unstained). Bar, 10 μm.

FIG. 3.

Overview of potential risk or protective factors influencing the horizontal or vertical transmission of Neospora caninum and the occurrence of exogenous or endogenous N. caninum-associated abortion. In this diagram, naïve cattle are gray, postnatally infected cattle are orange, and vertically infected cattle are red.