Introduction

Invasive Species Defined

What's Being Done

 National Invasive Species Information Center

Submodule 6: Microbes and Fungi -- the Pathogens

Animal Pathogens

Nonindigenous animal pathogens have changed the course of human history. Entire herds of livestock have been lost due to the introduction of diseases into the U.S. There has recently been concern that the surveillance necessary to prevent the introduction and spread of exotic animal pathogens in the U.S. is falling behind what is needed.

Let’s look at some examples of nonindigenous pathogens that are currently infecting wild and domestic animals in the U.S.:

• Exotic Newcastle Disease (END), a fatal disease that can infect all types of birds, is caused by a virus belonging to the Paramyxoviridae family. The most common route of importation of the virus is through infected birds, which may not show evidence of disease. END, which is highly contagious, is said to be so virulent that it can kill birds showing no clinical disease symptoms. Death occurs in almost 100% of unvaccinated birds, and is frequent even in birds that have been vaccinated. There are high numbers of virus particles in all bodily secretions of infected birds, and the virus can remain intact for many days in a moist environment. Once the disease is detected entire flocks may be destroyed. In an outbreak in California in the 1970s, approximately 12 million birds were destroyed at a cost of $56 million. Establishing quarantines of bird movement in infected areas of the country commonly deters spread of the disease. In 2003, the Secretary of Agriculture removed areas in Nevada, Arizona, and Texas from quarantine; areas under quarantine in California were reduced.
• Avian Influenza (Orthomyxoviridae): The viruses that cause what is commonly known as “bird flu” occur naturally in the intestines of wild birds. While these wild birds rarely get sick from the disease, domesticated birds can become quite ill or die from an infection. The virus is very contagious and is shed in the secretions and excretions of infected birds. It can remain viable on moist surfaces (dirt or cages), and in water and feed. Highly pathogenic forms of the virus (known as the H5N1 subtype) have a mortality rate of over 90% in birds while less virulent forms usually only cause mild physical problems and perhaps a decrease in egg production. There were major outbreaks of the H5N1 subtype in Southeast Asia in late 2003 and early 2004 when over 100 million birds either died from infection or were destroyed in an attempt to contain the virus. By early 2006, the same strain had made its way west into the European Union in both wild and domesticated birds. A major outbreak of HPAI would be costly. Eradication of the 1983-84 outbreak in the Northeast resulted in the destruction of more than 17 million birds at a cost of $65 million; retail egg prices increased 30%. Recent outbreaks around the world include: 2004 Asia; 2003 The Netherlands; 2002 Chile; 1997-98, and 2003 Hong Kong; 1997 Italy.
• Avian pox (Avipoxvirus): Three strains of avian pox have been identified (fowl pox virus, pigeon pox virus, and canary pox virus); all can cause disease in birds ranging from mild to severe. Symptoms include the growth of wart-like lesions on the non-feathered parts of the bird’s body, and sometimes lesions on mouth, larynx, and trachea. The disease is most common in temperate regions in both wild and domesticated birds. Although the virus is thought to have existed throughout history, its occurrence in North American is relatively recent. It can be spread by contact with infected secretions and excretions, or when a mosquito bites a viremic bird (a bird with high levels of virus in the blood), and then bites a non-infected bird. The virus can remain viable in water and feed, and attached to clothing and hard surfaces. A vaccine is available for control of the disease in domesticated birds; this method is not feasible for wild birds.
• Whirling Disease (Myxobolus cerebralis): This disease, native to Eurasia, was first identified in North America in the 1950s and is caused by a parasitic protozoan. It is a potentially lethal infection of fish of the salmon family, and is more common in the young. Whirling disease presents with a myriad of symptoms including misshapen lower jaw and gill coverings, gaping mouth, a hump on the back just behind the head, darkened and misshaped tail, and the behavior of swimming in circles or “whirling” until death. The infecting organism has a complex life cycle that alternates between fish and aquatic oligochaetes, or worms. The disease is found in 22 states including the western states, the mid-Atlantic region, Michigan, Ohio, and Mississippi. Birds can transport this disease between bodies of water; it can also be carried on fishing equipment.
• Foot and Mouth Disease (Aphthovirus): FMD is a highly contagious and economically devastating disease of cattle and swine. It also affects sheep, goats, deer, and other cloven-hoofed (split-toed) ruminants. Clinically, symptoms include lameness caused by painful vesicles in the epithelium of the mouth, nostrils, interdigital spaces, and teats. The vesicles rupture leaving large denuded areas, which may become secondarily infected. Many affected animals recover, but the disease leaves them debilitated. FMD causes severe losses in the production of meat and milk. Because it spreads widely and rapidly and because it has grave economic as well as physical consequences, FMD is one of the most dreaded animal diseases for livestock owners. The U.S. Department of Agriculture (USDA) implemented an interim rule on February 21, 2001, prohibiting or restricting the importation of live swine and ruminants and any fresh swine or ruminant meat (chilled or frozen) or products from Great Britain, Northern Ireland, or Argentina. Products dated after January 14 (February 19, 2001, in Argentina) are not permitted entry into the United States. Ports of entry have been notified to enhance surveillance of travelers coming from Europe, particularly the United Kingdom (UK) because that area is now considered to be at high risk for FMD. All international travelers must state on their Customs declaration form whether or not they have been on a farm or in contact with livestock and if they are bringing any meat or dairy products from their travels back with them. APHIS officials will inspect the baggage of all travelers who indicate they have been on a farm or in contact with livestock and any soiled footwear must be disinfected with detergent and bleach. It is estimated that the resent outbreak of FMD in the UK cost over $30 billion due to productions shortfalls and destruction of livestock. In early 2006, restrictions of importations from were in place (meat was allowed to be imported from Northern Ireland).