[Vertebrate Pests] Rodents and LCMV

This past spring you probably read on the Internet (or heard on the news) that seven people died from a rodent-transmitted viral disease known as LCMV. This abbreviation refers to a virus that causes an illness referred to as Lymphocytic choriomeningitis (LCM). This news generated many questions from the public to pest professionals everywhere regarding the risk associated with the LCM virus from rodents in and around our buildings, as well as from pet rodents purchased from pet stores.

Let’s take a look at LCMV and how it impacts our clients and our services in the pest management industry.

LCMV. Lymphocytic choriomeningitis is a rodent-borne, viral infectious disease that causes meningitis (inflammation of the membrane that surrounds the brain and spinal cord), encephalitis (inflammation of the brain) or meningoencephalitis (inflammation of both the brain and meninges).

The causative agent of LCM is a virus belonging to the viral family Arenaviridae that was initially isolated in 1933. It is worth noting that rodent-borne Arenaviruses were responsible for the death of seven people in California in 2001, resulting in extensive media coverage.

SYMPTOMS OF LCMV. Fortunately, studies have shown that for the majority of cases where LCMV is contracted by healthy persons, the infection usually is either asymptomatic (no outward signs or symptoms) or the virus causes mild self-limited illness.

Even with the more serious (but uncommon) cases of LCMV, the infection for healthy adults is rarely fatal. But more severe cases are no walk in the park. Victims suffer from fever, malaise, anorexia, muscle aches, headache, nausea and vomiting. Occasionally, sore throat, cough, joint pain, chest pain, testicular pain and parotid (salivary gland) pain accompany the initial phases of infection. After a few days, the infection enters a remission, but is then followed by a second phase, consisting of symptoms of meningitis (e.g., fever, headache and a stiff neck) or characteristics of encephalitis (e.g. drowsiness, confusion, sensory disturbances and/or motor abnormalities, such as paralysis).

For pregnant women, LCMV can be particularly troublesome. Infection during pregnancy can result in transmission of the virus from mother to fetus, which, in some cases, can result in miscarriage, mental retardation and several other serious illnesses to the fetus or newborn.

DISTRIBUTION OF LCM. Cases of LCM have been reported in Europe, the Americas, Australia and Japan, and may occur wherever infected rodent hosts of the virus are found. However, epidemiologists state that LCM has historically been under-reported, often making it difficult to determine incidence rates or estimates of prevalence in any particular area.

Some serologic studies conducted in urban areas have shown the prevalence of LCMV infection among humans is estimated to range from 2 to 10 percent.

Studies conducted in the 1990s (by the well-known epidemiologist Jamie Childs and others) in a few urban areas of the United States resulted in prevalence at about 5 percent. But, a universal profile of the LCMV prevalence of the urban areas of the United States has not been conducted.

THE ROLE OF RODENTS. The house mouse (Mus domesticus) is the primary reservoir for the LCMV. Research has shown a prevalence of infection in mice ranging from a low of 3 percent to a relatively high infection prevalence of 40 percent. As you might expect, the infection prevalence tends to be highest in areas where the virus is well established and has become widespread among rodent populations.

Mice can become chronically infected by maintaining the virus in their blood and/or persistently shedding virus in their urine, a common characteristic of other Arenavirus infections in rodents. Chronically infected female mice usually transmit infection to their offspring, which in turn become chronically infected.

LCMV also is associated with other types of rodents such as hamsters and guinea pigs, and these pet rodents can become infected after some type of contact with infected house mice. These pet rodents also have been implicated in human infection (as discussed below).

Infected rodents may be asymptomatic, or in the more severe infections (or within the more vulnerable animals), they may become ill from the virus.

People may become infected with LCM should they inhale infectious aerosolized particles of dried rodent urine, feces or saliva. Infection also can occur by ingesting food contaminated with the virus, by contamination of mucus membranes with infected body fluids, or by directly exposing cuts or other open wounds to virus-infected blood. Person-to-person transmission has not been reported, with the exception of vertical transmission from an infected pregnant woman to fetus.

RECENT LCMV DEATHS. Because of hectic schedules these days, most of us have the time to only scan headlines of the stories in the news. With the recent deaths from LCMV, the headlines on the Internet and in the papers simply stated, "Several deaths due to a rodent-borne virus." For many in the public sector, this conjured up thoughts of Hantavirus (as per the 1993 outbreak). Following these headlines, clients of pest professionals began asking questions relating to their risk to LCMV should there be mice around their homes, offices, schools and so forth, as well as to the risk to their children from pet hamsters, gerbils, mice and rats.

However, in the deaths that occurred this spring and in the past few years, the cases were not directly associated with house mouse infestations in homes (or if wild house mice were involved, it is not known to what extent).

In the spring of 2005, in the LCMV cases from Massachusetts and Rhode Island (and similar to previous cases in 2003 from Wisconsin), all of the patients had received solid organ transplants from one common donor. All four organ recipients subsequently contracted LCMV. Health officials indicated the source of infection was likely from an infected pet hamster in the donor’s home.

WHAT TO TELL CLIENTS. How should we address questions we may receive from our clients? I suggest having the following discussion with your clients:

1. Even though LCMV is associated with house mice and some other rodents (gerbils, hamsters, etc.), the disease is currently considered rare (although note the following discussion).

2. Typically, the virus causes little or no illness in healthy people but can be deadly for those with weak immune systems (e.g., cancer patients, transplant recipients) who take immune-suppressing drugs to keep them from rejecting their new organs.

3. Nevertheless, as every pest professional knows, it is always desirable to keep structural rodent infestations (homes, offices, schools, etc.) ideally to zero, or to levels as low as possible. In turn, this reduces the risk to not only LCMV, but to any other rodent-borne disease potential.

4. For questions regarding pet rodents or the purchasing of pets (gerbils, hamsters, mice and rats), suggest your client visit the Center for Disease Control and Prevention’s Web site at www.cdc.gov/healthypets/lcmv_rodents.htm

This site provides an exceptional Q&A section to pertinent concerns. If clients do not have access to the Web, they should call their local board of health for guidance.

Perhaps the last point to be made regarding this issue is that it re-emphasizes the importance of what we as pest management professionals do. Except for some research projects, no one follows behind you collecting all the mice and rats you eliminate with traps and baits to examine whether or not they might have transmitted some disease or illness to the people in that building or area.

Moreover, remember what some scientists list as low prevalence infection rates (say a conservative 5 percent) among urban rodent populations containing millions of individuals; low prevalence rates still results in very significant numbers of potential disease vectors.

Thus, even though we can’t measure a negative, just keeping these conservative numbers in mind, leaves little doubt as to the importance of the work of the everyday pest professional.

The author is president of RMC Pest Management Consulting and can be reached at rcorrigan@giemedia.com or 765/939-2829.