VERTEBRATE PESTS: Do Rats Transmit Hepatitis?

Recently, urban rats have been linked to hepatitis. This is the first time commensal rodents have been associated with hepatitis, although it is too early to jump to any conclusions about the significance of rats and this important human disease.

Still, this news warrants that pest professionals should take a moment to consider the disease hepatitis and examine the recent news about rats and the role they may play in transmitting hepatitis.

HEPATITIS 101. Hepatitis causes inflammation and injury to the liver (hepatic = liver; itus = inflammation). So far, six types of hepatitis have been identified, each categorized as A, B, C, D, E and G. Among these six types, hepatitis has many causes, including the misuse of alcohol and drugs, but viruses are the most common cause. Medical experts estimate that more than 300,000 cases of viral hepatitis occur each year in the United States alone.
Symptoms of hepatitis include nausea, fatigue, poor appetite and occasional abdominal pain and fever. The urine of hepatitis victims often becomes dark and their skin becomes jaundiced (a yellowing of the skin). 

The association between the hepatitis E virus (HEV) and urban rats came into the news in November 2001 at the annual meeting of the American Society of Tropical Medicine and Hygiene (ASTMH). Here, Dr. Robert Purcell, co-chief of the Laboratory of Infectious Diseases and Head of the Hepatitis Viruses Section of the National Institute of Allergy and Infectious Diseases, presented the preliminary findings of a possible link of HEV with city rats.

Hepatitis E virus is actually unrelated to the other hepatitis viruses. HEV is most associated with sporadic cases of enterically transmitted (i.e., via the intestines) acute hepatitis and is endemic in tropical and subtropical regions of Asia, Africa and Central America. HEV infection is self-limiting, lasting one to four weeks and is generally not life threatening. But, in pregnant women, an HEV infection can be especially serious with fatality rates ranging from 15 to 20 percent. The cases that have occurred in the United States are typically associated with travelers returning from developing countries. Still, researchers report that from 1 to 5 percent of healthy blood donors in the U.S. have HEV antibodies in their blood, while among the homeless populations in some inner cities, the presence of HEV antibodies range between 15 and 20 percent. Keep in mind that those individuals with antibodies have somehow been previously exposed to the virus.

THE STUDY. How do some inner-city persons and specifically, the homeless, become exposed to the HEV virus? To address this question, scientists considered city rats as a possibility because earlier studies indicated a high percentage of wild rats in the U.S. possessing antibodies against HEV (suggesting these rats were subject to previous infection). To study a possible link between city rats and those living in inner-city areas, researchers extracted blood sera from 80 rats collected from Orange and Los Angeles counties, Calif.; Baltimore; and Hawaii. They injected the sera of these wild rats into lab rats. Three of the injected rats with sera from the Los Angeles rats developed HEV.

But this is only the beginning piece of a complex puzzle. According to Purcell, so far these findings only demonstrate that wild rats can act as agents in transmitting a virus serologically related to HEV. So although it is possible that infected rats in inner-city communities may contribute to the high rates of humans with HEV antibodies, more work needs to be done. The next step is to clarify whether the rat-borne virus can be passed to humans via rat bites or other avenues.

CONCLUSION. Whether or not rats ultimately play a major role in HEV transmission and/or become responsible for establishing a greater presence of HEV remains to be seen. Nevertheless, this research should not come as a surprise to any pest management professional. Historically, rats and mice have been responsible for some of the most devastating diseases of all time. Domestic rodents have been implicated in about 58 diseases, representing a diverse range of pathogens. Viruses and bacterial organisms account for 19 and 29 of the pathogens respectively. In the past century, more than 10 million people have died from rodent-borne diseases.

Furthermore, if we look at just the past eight years, we remember that in 1993 deer mice were discovered to be the main rodent reservoir involved in the transmission of hantavirus pulmonary syndrome. In 1997, it was revealed that the ubiquitous house mouse is a significant cause of asthma-related diseases in susceptible individuals in inner-city homes. In 2000, wood rats (“packrats”) were suspected in the transmission of a rare group of viruses (called arenaviruses) that caused several deaths in California. And now, we have this possible link between urban rats and hepatitis.

As the passing of time allows epidemiologists more opportunities to delve deeper, it seems the association between rodents and diseases continues to increase. Thus, can there by any doubt as to the significance of the pest professional’s work in urban communities? With every rat or mouse eliminated from a home, or the local supermarket or restaurant, who knows what other yet-to-be-discovered health threat you help to prevent?

The author is president of RMC Pest Management Consulting and can be reached at rcorrigan@pctonline.com.