Detection of Toxoplasma gondii in the milk of experimentally infected lactating cats
Introduction
Several studies have documented that infection of kittens with Toxoplasma gondii can occur transplacentally or in the neonatal period (Dubey and Hoover, 1977, Dubey et al., 1995, Dubey et al., 1996, Omata et al., 1994, Powell and Lappin, 2001, Sato et al., 1993). Lactational transmission was suggested in one study where passage of T. gondii from queen to kitten was more common when kittens were allowed to nurse (Dubey et al., 1995). In another study, lactational transmission was considered likely because infection in kittens occurred even when queens were infected with T. gondii as late as 1 day prior to parturition (Powell and Lappin, 2001). Infection by ingestion of oocysts from feces or in the perianal area was not considered likely since feces were removed before oocysts had time to sporulate, and newborn kittens have been shown to remain free from infection even when housed with kittens inoculated with large doses of T. gondii (Dubey and Frenkel, 1972, Dubey et al., 1995).
Tachyzoites of T. gondii have been found in the milk of several species, including sheep, goats, cows, and mice (Dubey, 1998, Pettersen, 1984, Tenter et al., 2000). Infection in humans has been documented from ingestion of raw goat milk (Sacks et al., 1982, Skinner et al., 1990) and it is suspected that lactational transmission can occur from humans as well (Bonametti et al., 1997). Recently, tachyzoites have been shown to be infectious orally to cats and mice (Dubey, 1998) further supporting the likelihood of infection by milk ingestion in these species. The purpose of this study was to determine if T. gondii could be detected in the milk of experimentally infected queens by bioassay or polymerase chain reaction (PCR).
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Materials and methods
Six young adult female, specific-pathogen free, domestic shorthair cats were purchased (Liberty Research, Inc., Waverly, NY). The experimental protocol was approved by the Animal Care and Use Committee at Colorado State University. Queens were either purchased while pregnant or were bred in house with a male from an internal breeding colony. All cats were tested and shown to be seronegative for T. gondii IgM and IgG (Lappin et al., 1989).
The Mozart, Maggie, and ME-49 strains of T. gondii were
Results
The PCR consistently detected 10 tachyzoites/ml in PBS and 100 tachyzoites/ml in samples added to cow’s milk. All infected queens shed T. gondii oocysts (Table 1). Queen 6 died of disseminated toxoplasmosis 15 days after being fed tissue cysts. Oocyst shedding ended 11, 7, and 15 days before parturition in cats 1, 2, and 5, respectively and 2, 12, and 0 days after parturition in cats 3, 4, and 6, respectively. Duration of oocyst shedding ranged from 2 to 6 days (Table 1). Of the six queens, T.
Discussion
This study documents that T. gondii can be found in the milk of experimentally infected cats. Strain of T. gondii, number of infecting organisms and the interval between parturition and feeding of tissue cysts to cats apparently did not affect excretion of T. gondii in milk. Contamination of milk samples with oocysts from the queen’s fur is unlikely since feces were removed daily and most of the positive milk samples were detected between 14 and 47 days after completion of oocyst shedding.
Conclusion
This study documents that T. gondii can be found in the milk of experimentally infected cats.
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