Anthrax in Cattle: The Risk to Humans

There are 3 main types of anthrax – cutaneous, gastrointestinal and respiratory. All three types of infection can occur in animals and humans. Spores are an important factor in transmitting infection, and animals usually become infected through grazing in areas where large numbers of spores are present in the surface of the soil (link to anthrax and cattle). Therefore natural infection in humans is not likely to occur unless they are in contact with infected animals or animal products.

Infection in animals is usually gastrointestinal, and the most likely route of infection in grazing animals is through ingestion of spores during dry periods following flooding. Spores are brought to the surface during periods of heavy rainfall and remain there and become concentrated during dry spells. Ingestion alone does not necessarily result in infection – the spores require a lesion of some sort to gain entry into the tissues. Gastrointetinal lesions may occur when grazing on dry, spiky, gritty grass that grows close to the soil – infection occurs where spores have also been deposited on the soil.

Grazing animals may also become infected through inhalation of spore-laden dust (pulmonary anthrax), although infection by this route is much less common than through ingestion. Animals that feed on the carcasses of dead animals can also become infected during outbreaks in grazing animals.

Humans become infected through contact with infected animals or animal products such as carcasses, hides, wool, hair and bone meal. Therefore, in areas where infection in livestock is uncommon, human infection is also rare.

The World Health Organization (WHO) reports higher incidence of infection in certain areas of Canada such as the MacKenzie Bison Range, North West Territory and Wood Buffalo National Park in northern Alberta, with sporadic outbreaks occurring in southern Alberta and Saskatchewan. In the U.S., sporadic cases occur in South Dakota, Nebraska and Oklahoma, with more persistent outbreaks in western Texas. In other areas of the world outbreaks occur more consistently – Central and South America, Mexico, South Africa, Middle East, Soviet Union, southern India, and south-east Asian countries (Vietnam, Cambodia, western China, Thailand).

The most common form of natural human infection is cutaneous anthrax, accounting for at least 95% of cases world-wide. Cutaneous anthrax is readily treated with penicillin and a number of other antibiotics. Without treatment, 10-20% of cutaneous infections may be life-threatening. Contact with the vegetative form of the bacteria in the fluids and tissues of sick or dying animals, or with spores in dead carcasses, meats, hides, hair, wool or bone does not guarantee infection. Infection requires a skin lesion (cut, scrape, etc.) in order to gain entry to the tissues. In 2-3 days (may occur as early as 9 hours or as long after as 7 days) a pimple-like red elevated area appears, followed 1-2 days later by a ring of blister-like, watery fluid-filled vesicles with swelling in the surrounding area. By 5-7 days, an ulcer forms (eschar) (see photo). By approximately 10 days, the eschar begins to heal and may take up to 6 weeks to resolve. Treatment at this stage does not speed healing. Without treatment a small number of cases may develop systemic infection.

Gastrointestinal and pulmonary anthrax have much higher mortality rates than cutaneous anthrax, often because they are more likely to go unrecognized and untreated. Treatment in the early stages of either infection is very effective; however, the disease progresses rapidly, and in the latter stages of infection treatment is often ineffective.

Gastrointestinal infection may occur following ingestion of raw or improperly cooked meat from sick or dead animals and symptoms are similar to other food-borne illnesses –

nausea, vomiting, fever, abdominal pain. Cases may be mild or severe – in severe cases the mortality rate is approximately 50% even with treatment.

Pulmonary anthrax is even more likely to be misdiagnosed as the initial stage of infection involves flu-like symptoms – mild fever, fatigue and malaise lasting one to several days. Without treatment at this stage, infection progresses rapidly to difficulty breathing, disorientation, toxemia and death. Naturally acquired pulmonary anthrax in humans is extremely rare.

Anthrax and Cattle: Terror on the Prairies.

Like most people, when I think of anthrax, I think of white powder, mail and terrorism plots. If I was the extremely paranoid type, the recent news reports of cattle dying of anthrax infection on farms in Saskatchewan and Manitoba might have me wondering whether our food-chain is now being targeted by terrorists.

The latest threat to Canada’s beef industry, following the mad-cow hysteria of the past few years, is anthrax. the Canadian Food Inspection Agency (CFIA) has reported 644 dead animals on 136 farms in Manitoba and Saskatchewan, most of these cattle. Why? Did terrorists tire of licking envelopes? Are they frustrated with the speed at which snail-mail is delivered? No. This recent outbreak of infection in cattle is naturally occurring, unrelated to any sort of conspiracy.

Anthrax is a zoonotic infection, primarily infecting grazing animals (herbivores) who ingest spores of the bacteria, Bacillus anthracis, found in soil. Bacillus anthracis in its spore form is extremely resistant to harsh environmental conditions such as drying, heat, cold and chemical exposure. This is the reason that anthrax spores have been popular throughout history as an agent of biowarfare and bioterror.

Not all bacteria have the ability to form spores, but for those that do, when environmental conditions become uninhabitable, the bacteria enters into a dormant or nonactive state. Once conditions improve, such as when the spore is inhaled into a nice warm moist nutritious body, animal or human, the spore changes back to its vegetative or active state and begins to grow and multiply. As Bacillus anthracis multiplies, it produces toxins that cause damage and are potentially life-threatening. Infected cattle die quickly once infected so that sick animals are not often seen.

The current outbreak is the largest recorded outbreak of zoonotic anthrax occurring over the largest area in Canada. The last largest outbreak reported by the CFIA was in 2000, involving 28 cattle – 24 in Manitoba, 3 in Ontario and 1 in Saskatchewan. There were also 10 deaths in other animals – 6 in bison (5 in Alberta and 1 in the North West Territories) and 4 in black bears, moose and wolves in Alberta. However, deaths are sporadically seen most years across the Prairie provinces. Why are we seeing so many deaths in livestock this year? The abundant rain and flooding in Saskatchewan and Manitoba this spring and early summer have been extremely favorable for bringing anthrax spores to the surface of fields and meadows where animals graze. Spores reportedly can live in the soil for 50 years or more. Once ingested by animals grazing in spore-rich areas, the bacteria causes a severe gastrointestinal infection, which very often leads to death.

What is the threat to humans? Check in next week to find out whether there is reason for concern.

The Science of Autumn or Fall Leaves: Why Do Leaves Change Colour and Fall From the Trees?

Autumn’s beauty is clear for all to see, the myriad shades of red, yellow and brown lifting the heart on a cold but bright October morning. But the curious mind wonders “Why?” Why do the trees go through this process every year, only to grow fresh leaves every spring? And why such a variety of colours and shades – of which any artist would be proud?

Using Chlorophyll

The green leaves of summer contain chlorophyll, which drives photosynthesis – the molecular factory transforming carbon dioxide and light into glucose – which gives energy to the plant and cellulose for growth. When summer ends and autumn arrives, it is the short days which trigger the changes in deciduous trees. The chlorophyll is taken back from the leaves to be recycled, but the leaves become not just superfluous, but a liability.

Abscission Zones

In order to exert a force of suction, to draw water from the ground during the summer, leaves sweat through their high surface area. In winter these same leaves could cause the trees to dry out and die, so they must be removed. The scientific process of leaf-removal is known as abscission. When the shorter days of Autumn arrive, a number of chemical changes occur and the abscission zone at the base of the year begins to swell, cutting off the flow of nutrients from the tree to the leaf and vice-versa. The zone then begins to tear, the leaf falls off or is blown away, and a protective layer seals the wound, preventing water evaporation and entry of bugs.

Anthocyanins and Aphids

But why do the leaves go so many different colours? The removal of the chlorophyll reveals other colours in the leaf – yellow, orange and brown – but some leaves turn red or purple for another important reason. The shorter days which trigger the process of abscission, also initiate another process in the leaves of certain trees to produce a group of chemicals called anthocyanins, which are deep red or purple in colour. This is not, however, just vanity on behalf of the tree.

In fact, the red colours are used to conceal the shades of yellow which attract aphids. So, trees which are more susceptible to aphids, or are native to areas where aphids are more of a problem, are able to confuse their enemies and survive to grace another spring.