Fear of contracting rat lungworm disease from eating fresh local greens has driven many people to avoid these healthy foods. Articles concerning the involvement of rats, worms and slugs in the spread of the disease seem to have spawned near panic around these animals and the possibility of contracting the disease from eating greens. Though caution is advised in selecting and consuming vitamin-rich foods such as kale, chard and hearty lettuces, avoidance is not necessary.
Fear of contracting rat lungworm disease from eating fresh local greens has driven many people to avoid these healthy foods. Articles concerning the involvement of rats, worms and slugs in the spread of the disease seem to have spawned near panic around these animals and the possibility of contracting the disease from eating greens. Though caution is advised in selecting and consuming vitamin-rich foods such as kale, chard and hearty lettuces, avoidance is not necessary.
According the University of Hawaii publication “Avoid Contracting Angiostrongyliasis (Rat Lungworm Infection),” available online at ctahr.hawaii.edu/oc/freepubs/pdf/FST-35.pdf, “Avoiding eating fresh produce out of fear of contracting angiostrongyliasis is not the best preventive measure. Fresh produce is a primary source of bioactive nutrients and functional foods.”
Rather than avoid eating healthy food, a better plan is to be armed with information about the disease and to proceed with preventive practices against acquiring it.
First some information. The rat lungworm, Angiostrongylus cantonensis, is a roundworm that can cause eosinophilic meningitis, a disease with the scientific name angiostrognylaisis, that has a variety of symptoms.
Because the roundworm enters the body through the digestive system, early symptoms may include stomach pain, nausea, vomiting, diarrhea or severe headaches. As the worm moves into the nervous system, other symptoms may develop including neck and back stiffness, skin tingling, a sensitivity to light and hallucinations. Though rare, severe cases can lead to a coma or death.
Though the disease’s symptoms have been anecdotally reported in as high as 15 percent of the population in some areas of Puna, the disease is actually very rare in the state. Despite a single case on Oahu in 1958, the Hawaii Department of Health did not start data collection and tracking until 2005. This followed a year with fewer than nine confirmed cases in East Hawaii and one in Kona. The latest data shows that 90 percent of the cases in the state occur in East Hawaii.
2004 was the first year that the Asian semi-slug Parmarion martensi was found in Puna. This slug has been shown to be between 75 percent and 85 percent infested with rat lungworm. Its presence probably caused increased incidences of infection. Another intermediate host for the worm is the Cuban slug, Veronicella cubensi, with less than 35 percent showing infestation. African snails and flatworms are also hosts but with lower percentages of infestation and less prevalence in human populated areas.
The worms first infect rats. As they multiply in their primary host, some pass through the digestive system and are eliminated. Slugs, snails and flatworms may eat infected rat feces and become secondary hosts. If any infested part of the mollusks or worms is consumed by a person, that person becomes a tertiary host and one where the rat lungworm cannot live. It can however cause a lot of pain before it dies.
The best way to reduce your chance of infection is to eliminate the earlier hosts. Controlling the rat population by reducing their food supply and maintaining cats and traps is a good start. Collecting slugs with gloved hands and killing them in soapy water, eliminating their hiding places and using organically approved and pet-friendly slug baits containing iron phosphate can greatly reduce the mollusk population. With these hosts under control, the chances of infection are greatly reduced.
The rest of the preventive measures require that those who pick and consume greens have good eyesight and are vigilant. When picking, inspect greens for slugs or snails or their eggs. To be totally safe, do not pick any mollusk damaged leaves or those with trails. Wash and reinspect all greens before refrigeration and if you suspect that snails or slugs could be present, repeat before eating. For noncommercial operations, the Health Department recommends washing in cool, potable water. With softer lettuces, spraying with water can be equally effective. For larger operations, water sanitizers are recommended at the approximate rate of one teaspoon per gallon of water. Some sanitizers contain chlorine bleach but more environmentally friendly ones contain citric acid or hydrogen peroxide. Though their efficacy against rat lungworm has not been proved, using these can help sanitize against other pathogens. More information can be found in a downloadable publication at ctahr.hawaii.edu/oc/freepubs/pdf/FST-39.pdf.
Hopefully, this information will serve to reduce fears and get folks happily and healthfully enjoying local greens. By encouraging well-informed caution we can also hope to decrease the incidence of rat lungworm disease in our population.
Tropical gardening helpline
Ann asks: My hydrangea has always produced blue flowers. Recently, after I put some gravel in an area above the plant, the blossoms seemed to be very pale, kind of an ivory color. Could the gravel have affected the plant and caused the blossom color to change? If so, is there anything I can do?
Answer: Yes, the water running off the gravel probably changed the pH of the soil around your hydrangea causing the blossom color change. The pH of the soil directly affects the availability of aluminum in the soil to your plant. Where aluminum is readily available, the blossoms will likely be blue. Where less or no aluminum is available, the flowers are likely to be paler and in some cases pink.
Fertilizing with a product for acid-loving plants will probably help. Adding mulch or other organic matter in the root zone can help acidify the soil and initiate blossom color change back to blue. None of these remedies will be instant, but within a month of application of each of these you should see a change in the blossom color back to blue. If not, your plant may have root rot or a disease that could be causing the problem. Watch for symptoms that might give you clues to other problems if the added fertility doesn’t work.
Email plant questions to konamg@ctahr.hawaii.edu for answers by Certified Master Gardeners. Some questions will be chosen for inclusion in this column.
Diana Duff is a plant adviser, educator and consultant living on an organic farm in Captain Cook.