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The lungworm’s genome may spell R-E-L-I-E-F for the coughing cow

On the heels of last month’s sequencing of the cattle tick’s genome comes the report of a draft genome for lungworm, Dictyocaulus viviparous. This is good news for producers of dairy and meat from cattle and other ruminants such as elk and deer.

Unlike the tick study, the lungworm genome research does not come with a nicely packaged prototype vaccine, but it does add important basic understanding of the lungworm’s biology that the authors hope will allow for improved drug testing in the near future.

The microscopic lungworm may have a perfect – if rather repulsive – life cycle. Its ability to travel different systems in different organisms reads like a C.V. of language mastery. Respiratory system? Check. Lymphatic system? Check. Circulatory and digestive systems? Check, check. And the fungal reproductive system? Yes, check that one too.

From the cow’s perspective, the lungworm’s parasitic cycle begins when it is consumed as part of a grass meal. In reality, when it is ingested, the lungworm is actually in its third of five larval stages (see graphic below). From the stomach, it will migrate to the lymph system, where it molts to larval stage 4. Then it penetrates the lungs, where it molts to stage 5 and then to adult. Eggs laid in the lungs hatch to larval stage 1, at which point they are coughed up by the cow, swallowed and expelled with feces. The lungworm’s next two stages take place outside the animal and with the aid of a fecal fungus, which it also invades, getting into the developing spores that are later dispersed into the surrounding grass. At this point, it reaches stage 3 once again and the cycle is complete.

The life cycle of Dictyocaulus viviparus

Image of the life cycle of Dictyocaulus viviparus

For the purposes of the genomic study, a strain of lungworm from Germany was selected because it had been the subject of other gene expression work and tested with a recombinant vaccine. It turns out that the lungworm’s genome is not particularly large – smaller than most other parasites of the gastrointestinal tract. The team was also able to identify “proteins that are likely to play important roles in host-parasite interactions” as well as “molecules that may be investigated as drug targets” for future prevention, treatment and control. Such methods could include ways to disable the parasite’s ability to interact with its animal or fungal hosts.

The timing couldn’t be better – as the paper points out, there is evidence to suggest that the lungworm may be developing resistances to drug treatments as a result of excessive and widespread use.

Drug resistance could be potentially disastrous for farmers, particularly in regions where calves are routinely given a prophylactic treatment against lungworm, preventing the herd from developing an immunity to lungworm infections later in life.

Among the illnesses that can affect cattle and other ruminants, the bronchial infection, sometimes called “hoose” or “husk”, caused by lungworm is among the worst. Most serious among young animals, the infection can result in severe respiratory distress, secondary complications and death. Studies in the UK, where lungworm illnesses have been problematic in the past year, estimate that an outbreak of lungworm costs £160 ($320) per animal in treatment costs, mortality and reduced milk and meat production. And if more than a third of the herd is affected, the farmer is operating in a net loss.

Cough. Cough. Indeed.

Graphic of Lungworm Life Cycle from Scientific Reports 6, Article number: 20316 (2016) doi:10.1038/srep20316

The lungworm’s genome may spell R-E-L-I-E-F for the coughing cow

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