Deadly Weed Invaded Uganda (Aptly Named Congress Weed)

AN alien weed that harms human beings, kills livestock and chokes crops has invaded Uganda. Congress weed, scientifically known as Parthenium hysterophorus, has been seen rapidly multiplying in several spots especially along the highway across Uganda from Busia and to Kabale.

Dr. Gad Gumisiriza, head of the invasive species project in the agriculture ministry, said the weed has so far been detected in at least 12 districts.

“This is a very aggressive weed which requires quick response. If you delay it can grow and get out of hand.” The most affected areas are Busiu along the Tororo-Mbale highway and Busia border town, each having over two acres of the weed. In Busia, a charcoal burner got a severe skin reaction and only improved after being hospitalised.

Other affected areas include Karengare in Kabale district, Mbarara town, Bugembe town council near Jinja, Ibanda, Namutumba along Tirinyi road, Busesa in Iganga district, Namulemba in Bugiri district and Queen Elizabeth National Park in Kasese district. At Makerere University Kampala and Masaka town, two decorators were found growing congress weed as flowers without knowing it is a dangerous alien species. Witchdoctors also use the plant to invoke evil spirits, Gumisiriza said. Saturday Vision recently saw two herbal gardens in Bugembe where diviners have planted the weed.

Despite looking beautiful and smelling sweet, congress weed is among the world’s 10 most dangerous weeds. On contact with the human body, it causes a burning effect that can peel off the skin. Human beings who inhale pollen from the flowers can get an asthma-like illness or persistent flu-like symptoms. Cattle that eat it produce foul-smelling milk or even die. Gumisiriza said the weed can reduce maize yield by 40-60%. It can also reduce the amount of pasture in a grazing area by 90%.

The congress weed is thought to have been introduced into Uganda from Mexico through Ethiopia and Kenya. It accidentally got to Ethiopia through relief grain imported from Mexico during the great famine that hit the Horn of Africa in the mid 1980s. It is dispersed mainly by long distance trucks, rivers, water streams and storm water (floods).

The Jinja district production and marketing officer, Dr. Stephen Kiwemba, was shocked by how fast the weed multiplied in Bugembe.

“When we came here in December, the seedlings were not as many as you can now see,” said Kiwemba.

The weed can grow to the height of an adult and produce tens of thousands of seeds in one to two months. The seeds germinate easily but if the ground is not moist, it can remain viable (able to germinate) for up to 20 years. “The situation may not be as simple as we had earlier thought,” said Kiwemba. “We are headed to decline in agricultural productivity, food insecurity and poverty will set in as a result.”

Nalongo Zamu Mukoda, said the weed resembles another local herb known as buza. She said they had turned to the new weed because the indigenous look-alike is getting extinct.

So far, Kiwemba has organised a meeting in Bugembe to create awareness about the weed. But despite mobilisation by LCs, the locals are reluctant to attack the weed, except if it grows around their homes. A group of boda boda riders at Bugembe told Saturday Vision that they could not stop their money-minting routines to go uprooting the weed.

LC1 chief for Katende West in Budumbuli-Bugembe, Siraje Kisuule said for better results the Government should provide funding to fight the menace.

“It is important to intervene today instead of waiting until the problem is out of hand,” said Kisuule. In Busia, the communities are organising to pluck off the weed and caution children not to touch it.

Kiyemba points out that while such local efforts are useful, controlling the weed requires a massive national programme. “The problem is that people are not looking at it as an issue. But if we remain reluctant it will become a bigger problem.”

Agriculture ministry officials agree with Kiyemba. According to Gumisiriza, the ministry is planning to deal with the weed using chemical spraying, uprooting it and bugs to kill the weed.

“We have prepared a programme to spray the weed in key areas. We have also contacted Kenya to see how we can handle the weed in the no man’s land at Busia border,” he said. “In the meantime, we are going to keep monitoring and creating awareness about the dangers of the weed.”

Parthenium: A wide angle view.(SEMINAR)(Parthenium hysterophorus L.)

The Indian Journal of Dermatology, Venereology and Leprology

Publication Date: 01-SEP-07

Author: Lakshmi, Chembolli ; Srinivas, C.

Byline: Chembolli. Lakshmi, C. Srinivas

Introduction

Parthenium hysterophorus L. (congress grass, congress weed, carrot weed, wild feverfew, the "Scourge of India") is an exotic weed that was accidentally introduced in India in 1956 through imported food grains.[sup] [1] It has become a common weed causing dermatitis of epidemic proportions.[sup] [2] The epithet "congress weed" refers to the US congress (who allocated the shipment for Pune, India).[sup] [3] In Pune, it found an ecological niche without natural enemies and spread rapidly along the canal banks, roads and railway tracks to become a major field weed.[sup] [4] Both rural and urban areas have been invaded by this weed. It is the leading cause of plant induced air-borne contact dermatitis in India[sup] [5] and has achieved major weed status in India and Australia within the past few decades .[sup] [6] The weed can affect human health, animal husbandry, crop production and biodiversity.[sup] [6]

Distribution

Parthenium hysterophorus is a native of the West Indies and North East Mexico.[sup] [7] During the last hundred years, it has spread worldwide [Table 1].[sup] [8],[9],[10] It is thought to have originated as a result of natural hybridization between Parthenium confertum and P. bipinnatifidum .[sup] [11]

Botanical Aspects of P. Hysterophorus

It belongs to the family Asteraceae/Compositae (Daisy family), which is one of the largest and most important families in the plant kingdom. The family includes troublesome weeds, ornamental annuals, herbaceous perennials, medicinal and food plants [Table 2].[sup] [12],[13] Fifteen species of Parthenium L. occur in America and the West Indies. One species, Parthenium hysterophorus L. was introduced to the Indian subcontinent. All contain allergenic sesquiterpene lactones (SQLs).

In South America, P. hysterophorus does not contain parthenin, but instead has hymenin, which is a diastereomer. However, in India, the plant contains large amounts of parthenin and ambrosin.[sup] [14] No cross reaction between parthenin and hymenin exists in humans and guinea pigs.[sup] [14],[15]

The plants of Compositae family have many tiny flowers (florets) clustered to form a flower head (capitulum). This flower head is surrounded by bracts (modified leaves) that form an involucre beneath or around a flower cluster [Figure 1].[sup] [12]

P. hysterophorus has two life cycles,[sup] [8]

*Juvenile or rosette stage *Mature or adult stage

Juvenile stage

It has a rosette with large, dark green, simple, radicle, pinnetisect small leaves and flowering is absent. The large lower leaves are spread on the ground like a carpet, without allowing any vegetation underneath it.

Adult stage

It is procumbent (trailing along the ground but not rooting), profusely branched, leafy herb resembling a bush or shrub because of its height (1-2.5m). The stem becomes tough and woody as the plant matures into a hardy bush. Enormous number of pollen grains (624 millions per plant) are produced by anemophilous (by wind) pollination. It is an extremely prolific seed producer with upto 25,000 seeds (achenes) per plant. The plant is thermo- and photo-insensitive; hence, it grows round the year except in severe winters; in other words, it survives environmental extremes. It is a rapid colonizer and competes out other vegetation in its vicinity within two growing seasons. It grows in almost all types of soil except near the seashore as the saline soil is not conducive to parthenium flowering.

Allergenicity

The allergens in Asteraceae are SQLs and thus the patients with contact dermatitis to Compositae can react to many other non-Compositae SQL containing plants [Table 2].[sup] [12],[13] The SQLs are found in the leaves, stems, flowers, and some pollens. The highest concentrations are found in trichomes which are present on stems, the underside of leaves and in the flowering heads.[sup] [12]

Cross-reactivity between SQLs does not follow any rules. No single SQL nor the commonly used " SQL mix" of three common SQLs (alantolactone, dehydrocostus lactone and costunolide) serves as a reliable screen for SQL allergy.[sup] [16] Therefore, the samples of the suspect plant should always be used while patch testing a patient.[sup] [11] Over 200 skeletal types and 1350 individual types of SQLs have been described, and each of these may have multiple functional groups attached to them.[sup] [12]

SQLs are characterized by the presence of a a-butyrolactone ring bearing an exocylic a-methylene group [Figure 2].

Human health

Around three decades ago, serious human health risks from P. hysterophorus were reported from Pune.[sup] [1] Several thousands of cases of allergic contact dermatitis with some fatalities have been reported.[sup] [1] An outbreak of epidemic proportion followed a dam burst.[sup] [2] "After 1-10 years of exposure to the weed, 10-20% of the population will develop severe allergenic reactions. There may be hay fever, asthma or dermatitis and can be caused by dust and debris from the plant as well as pollen."[sup] [17] The severity of dermatitis in India is greater in comparison to America because the plant grows more vigorously in India and contains large amounts of the sesquiterpene lactone, parthenin, which is absent in the plants in South America.[sup] [18],[19]

It clinically involves the adult males in both USA and India.[sup] [12],[20],[21] Studies have estimated a ratio of 20:1 between men and women.[sup] [3],[12] This cannot be explained in terms of degree of exposure since Indian women and children also work in fields. Possibly women and children are less frequently sensitized.[sup] [12],[21] However, the studies on plant dermatitis from India have shown a male-to-female ratio of 1:1 and 5:5:1.[sup] [22],[23] In a study from Minnesota, the large male preponderance appeared to change with the male-to-female ratio of 1.4:1.[sup] [24] Initially, the exposed sites of the face, neck and flexures are affected with erythema, blistering and intense pruritus resulting later in skin thickening, hyperpigmentation and development of a leonine facies.[sup] [1] Unexposed sites may get involved late in the course of the disease. A seasonal variation is initially observed with the dermatitis flaring in the summers corresponding to the growing season and disappearing in winters.[sup] [25] After several years, persistent pruritic lichenified dermatitis develops without seasonal variation. Winter exacerbation is seen in the months of September, October and November and may be due to the...

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