Pathogenesis of feline enteric coronavirus infection

Abstract

Fifty-one specific pathogen-free (SPF) cats 10 weeks to 13 years of age were infected with a cat-to-cat fecal-oral passed strain of feline enteric coronavirus (FECV). Clinical signs ranged from unapparent to a mild and self-limiting diarrhea. Twenty-nine of these cats were FECV naïve before infection and followed sequentially for fecal virus shedding and antibody responses over a period of 8-48 months. Fecal shedding, as determined by real-time polymerase chain reaction (RT-PCR) from rectal swabs, appeared within a week and was significantly higher in kittens than older cats. FECV shedding remained at high levels for 2-10 months before eventually evolving into one of three excretion patterns. Eleven cats shed the virus persistently at varying levels over an observation period of 9-24 months. Eleven cats appeared to have periods of virus shedding interlaced with periods of non-shedding (intermittent or recurrent shedders), and seven cats ceased shedding after 5-19 months (average 12 months). There was no change in the patterns of virus shedding among cats that were excreting FECV at the time of a secondary challenge exposure. Four cats, which had ceased shedding, re-manifested a primary type infection when secondarily infected. Cats with higher feline coronavirus (FCoV) antibody titers were significantly more likely to shed virus, while cats with lower titers were significantly less likely to be shedding. Twenty-two kittens born to experimentally infected project queens began shedding virus spontaneously, but never before 9-10 weeks of age. Natural kittenhood infections appeared to be low grade and abortive. However, a characteristic primary type infection occurred following experimental infection with FECV at 12-15 weeks of age. Pregnancy, parturition and lactation had no influence on fecal shedding by queens. Methylprednisolone acetate treatment did not induce non-shedders to shed and shedders to increase shedding.

Fig 1

Typical fecal FECV shedding patterns of cats demonstrating a persistent pattern of infection.

Fig 2

Typical fecal FECV shedding patterns of cats demonstrating an intermittant pattern of infection.

Fig 3

Typical fecal FECV shedding patterns of cats demonstrating a self-limiting (recovery) pattern of infection.

Fig 4

Levels of virus shedding prior to and after reinfection (arrow).

Fig 5

One-way analysis of levels of fecal FECV shedding in a group of four cats that were shedding very low or non-detectable levels of virus prior to infection. Virus levels following reinfection were higher at all time points than they were prior to infection, but because of the small group size, only weeks 3 and 4 were significantly different.

Fig 6

One-way analysis of levels of fecal FECV shedding in a group of 15 cats that were shedding virus at the time of their secondary challenge exposure. There was no significant change in virus shedding following reinfection.

Fig 7

One-way analysis of the mean peak levels of FECV fecal shedding during primary infection in cats infected at 2–4 months of age, >2<8 years of age, and >8 years of age.

Fig 8

FCoV indirect IFA antibody titers in serum collected from cats over a 12–24 month period. Their fecal FECV shedding status was measured at the same time.

Fig 9

Fecal virus shedding levels in kittens born to project queens. Kittens were infected naturally at 9–10 weeks of age, but this infection appeared transient. Kittens were experimentally infected at 10–17 weeks of age (average 13 weeks).

Fig 10

Average levels of FECV fecal shedding before and after parturition in seven queens during nine pregnancies.

Fig 11

Levels of fecal FECV in cats that were positive shedders and treated with two injections of methylprednisolone acetate at week 0 and 4. There was no significant difference in levels of virus shed in the feces after treatment.