Zoonotic concern: Lymphocytic Choriomeningitis Virus in Rodents

Introduction

The physical and psychological benefits of pet ownership have been well established (8), however close contact with pets is not without risks, including the potential for transmission of zoonotic disease. Rodents can carry a number of potential pathogens, including lymphocytic choriomeningitis virus (LCMV) (Fig 1). This rodent-borne viral infectious disease is caused by the single-stranded RNA virus, arenavirus (9,11).

Figure 1. Rodents can carry lymphocytic choriomeningitis virus. Photo credit: Tiia Monto [CC BY-SA 3.0 (http://creativecommons.org/licenses/by-sa/3.0) or GFDL (http://www.gnu.org/copyleft/fdl.html)], via Wikimedia Commons.

Rodent-borne disease

Lymphocytic choriomeningitis virus is found worldwide because of its association with its natural host and reservoir, the house mouse (Mus musculus, Mus domesticus) (5,7,9,11,16). The common house mouse may be infected and shed virus without ever showing any signs of illness. Approximately 5% of mice in the United States are estimated to carry LCMV (3,11).

Other rodents, such as the hamster and guinea pig (Cavia porcellus), can also serve as disease reservoirs after they are exposed to wild mice infected with LCMV (16). Several outbreaks of LCMV infection in humans have been linked to exposure to persistently infected hamsters (16).

Infected rodents are typically asymptomatic, but clinical signs may include weight loss, sensitivity to light, and central neurologic signs, such as tremors or seizure activity (11). Lymphocytic choriomeningitis is also a potential cause of pelvic limb paresis or paralysis in guinea pigs (14).

Transmission to humans

Humans are infected with LCMV by direct contact with rodents, inhalation of aerosolized particles, or exposure to surfaces or materials contaminated by rodent urine, droppings, or saliva (4,5,9,16). Transmission can also occur when LCMV is introduced into broken skin or mucous membranes as well as through rodent bites (5,9,16). There is one case report of infection secondary to a penetrating needle stick injury with a LCMV-contaminated hollow needle in a laboratory worker (5). The seroprevalence of LCMV is estimated to range from 2% to 5% in human populations (9).

Clinical picture in humans

Immunocompetent

There are three potential outcomes when an immunocompetent individual is exposed to LCMV (Table 1) (4,16). Disease can be asymptomatic or mild with flu-like signs, such as fever, lethargy, anorexia, muscle pain, headache, nausea and vomiting (4,16). Disease is usually self-limiting, but sometimes develops into aseptic meningitis or meningoencephalitis, which usually resolves spontaneously (4,16).

Immunocompromised

Lymphocytic choriomeningitis virus can cause serious disease in the very young or the very old; individuals on radiation, chemotherapy, or high doses of steroids, as well as human immunodeficiency virus (HIV)-positive individuals, solid organ transplant recipients, and pregnant women (1,4,16).

TRANSPLANT PATIENTS

Lymphocytic choriomeningitis virus has caused severe or fatal disease among solid organ transplant recipients (7), leading to multisystem organ failure and very high fatality rates (Table 1) (16). In most cases, the exposure to rodents could not be identified (16), but one group of transplant recipients became ill after receiving organs from a common donor infected with LCMV by a pet hamster. Three patients died (1). Another transplant recipient developed LCMV meningoencephalitis complicated by hydrocephalus after contact with mice droppings (15).

CONGENITAL INFECTIONS

Women who acquire LCMV infection during pregnancy may transmit the virus transplacentally to the embryo or fetus (2,16). Infection can cause miscarriage, intrauterine fetal death, as well as birth defects. The virus exhibits a strong neurotropism leading to severe central nervous system or ocu­lar malformations; and severe neurologic sequela (4,16). Hydrocephalus, periventricular calcifications, chorioretinitis, blindness, and mental retardation are the primary characteristics of congenital LCMV infection (Table 1) (2,4,16). Congenital LCMV infection is thought to be rare, with less than 100 cases reported worldwide, however the true prevalence is unknown (4,16).

Prevention

Anyone who comes into contact with rodent urine, feces, saliva, or blood is potentially at risk for infection. Therefore, animal care providers, laboratory workers, and owners of pet mice, hamsters, or guinea pigs may be at risk for infection if these animals originate from colonies contaminated with LCMV or if the animals become infected from wild mice.

Take the following precautions to reduce the risk of LCMV infection (3,11):

• Always wash your hands with soap and water after handling rodents or their cages and bedding.
• Wear personal protective equipment and practice careful hygiene to reduce the risk of exposure when working closely with large numbers of rodents.
• Take proper precautions with regards to equipment and hygiene when cleaning rodent-infested areas.
• Avoid contact with wild mice and prevent infestations of wild rodents.
• If there is a rodent infestation in and around your home or facility, seal up rodent entry holes or gaps, trap and remove rodents, and remove potential food or nesting resources.
• Immunocompromised individuals, pregnant women, and women planning to become pregnant should avoid contact with rodents, including pet rodents (e.g., hamsters, guinea pigs) and rodent droppings.

References and further reading