All you should know about Leptospirosis

Pashu Sandesh, 16th June 2020

Dr M Areshkumar

Leptospirosis is the infection of the blood caused by the bacteria Leptospira. Signs and symptoms can range from none to mild (headaches, muscle pains, and fevers) to severe (bleeding in the lungs or meningitis).

WHAT ARE THE RISK FACTORS? 

The  conditions  that  are  favourable  for maintenance  and  the  transmission  of  the leptospirosis are as  follows, 

Reservoir and carrier hosts:

Leptospirosis has a very wide range of natural rodent and non-rodent reservoir hosts which include rabbits etc. The domestic animals such as cattle, buffalo, goat, sheep and pigs carry the microorganisms and therefore act as carriers of the leptospires. Together the rodents and the cattle excrete a large number of organisms in their urine and thus are responsible for the contamination of soil as well as large and small water bodies. 

Drainage, congestion and waterlogging:

Heavy concentrated rainfall leaves a lot of surplus water. Developmental activities like canal network, roads and railway lines obstruct natural drainage of rainwater causing its accumulation for longer periods. The waterlogged areas force the rodent population to abandon their burrows and contaminate the stagnant water by their urine.  The farmers and agricultural labourers working in the waterlogged contaminated fields acquire the infection.

Soil salinization:

Soil salinity and waterlogging are inter-linked problems. The salinity of the soil and alkaline pH provides a favourable environment for the survival of leptospires for months.

Soil temperature:

The soil of endemic areas, in general, has lower base saturation and the mean annual soil temperature at the depth of 50 cm is 22˚C or more and the difference between mean summer (June-August) and mean winter (December-February) temperature is less than 5˚C. This favours the survival of leptospires for long durations.

HOW IT GET TRANSMITTED?

• Leptospirosis is usually a seasonal disease that starts at the onset of the rainy season and declines as the rains recede. Sporadic cases may occur throughout the year.
• Leptospires are spread by the urine of infected animals (rodents, dogs, livestock, pigs, horses, wildlife).
• The bacteria can survive for weeks to months in urine-contaminated water and soil.
• People can be infected through
• Direct contact with the urine or reproductive fluids from infected animals
• Contact with urine-contaminated water (floodwater, rivers, streams, sewage) and wet soil
• Ingestion of food or water contaminated by urine or urine-contaminated water
• Transmission occurs through mucous membranes, conjunctiva, and skin cuts or abrasions. 
• Human-to-human transmission is very rare but has been documented through sexual intercourse and breastfeeding. The transmission has also rarely occurred through animal bites.
• High-risk activities can include wading, swimming, or boating in floodwater or freshwater (rivers, streams, lakes) that may be contaminated with infected animal urine. Some actions like prolonged immersion in, submerging head in, or swallowing contaminated water can particularly increase risk. 
• Other high-risk activities can include direct contact with animals and activities that can lead to skin abrasions and water or soil exposure, such as clearing brush, trekking, and gardening. 

Dogs: 

In most studies, the common reactivity to serovars in cases of canine leptospirosis reported in the past three decades has been to organisms in serogroups other than Canicola and Icterohaemorrhagiae. Dogs at risk for developing leptospirosis include those with,   

• Access to ponds, lakes, streams or standing water
• Exposure to urine from other infected animals, including: 
• Other dogs in shelters or other pet care facilities 
• Wildlife either through direct contact with urine or through contaminated water 
• Prevalence of canine leptospirosis has increased in recent years. 
• As many as 8.2% of dogs are shedding Leptospires, some asymptomatically. 
• Weather changes, population growth, and habitat encroachment have all increased human and canine exposure to pathogens and their carriers. 

Cats: 

Despite the presence of leptospiral antibody titres in the feline population, reports of overt clinical leptospirosis in cats are infrequent. Although cats seroconvert after exposure to leptospires, they appear to be less susceptible than dogs to both spontaneous and experimental infections.

WHAT ARE THE SINGS OF PETS AFFECTED WITH LEPTO? 

It may be peracute to sub-acute Disease with the clinical signs of fever, sore muscles, stiffness, shivering, weakness, anorexia, depression, vomiting, rapid dehydration, diarrhoea-with or without blood, icterus, spontaneous cough, difficulty breathing, PD-PU progressing to anuria, bloody vaginal discharge, death—without clinical signs. 

Chronic Disease:

In cases of chronic disease, no apparent illness noticed although fever of unknown origin, PD-PU—chronic renal failure are noticed. 

HOW TO PREVENT THE DISEASE?

• Prevention of leptospirosis involves the elimination of the carrier state. Unfortunately, wild animal reservoirs and sub-clinically affected domestic animals continue to harbour and intermittently shed organisms. 
• Control of rodents in kennels, maintenance of environmental conditions to discourage bacterial survival, and isolation of infected animals, therefore, are important to prevent the spread of the disease. 
• Adequate initial immunization, employing many of the available products, takes up to two to three injections, given 2 to 4 weeks apart, starting when pups are at least 9 weeks of age to produce immunity to challenge infection that will last at least 6 to 8 months, a time that depends on the product and serogroup. 
• Vaccines for leptospirosis are not recommended for pups less than 9 weeks of age, to reduce the severity of potential post vaccinal hypersensitivity reactions. 
• Humans with human immunodeficiency virus are at particular risk for severe infection; therefore, if they live in an endemic area, their dogs should be screened serologically for exposure and possible infection, and thereafter these animals should receive multivalent vaccination on a periodic basis. 
• The first line of leptospirosis prevention is to avoid exposure. Avoid wading, swimming, bathing, swallowing, or submerging head in potentially contaminated freshwater (rivers, streams) especially after periods of heavy rainfall or flooding. 
• Avoid contact with floodwater, and do not eat food contaminated with floodwater.
• If exposure cannot be avoided, wear appropriate personal protective equipment (PPE) (rubber boots, waterproof coveralls/clothing, gloves). Cover open wounds with waterproof dressings. 
• Treat unsafe or potentially contaminated drinking water by boiling or chemically treating.
• Keep rodent populations (rats and mice) or other animal pests under control. Do not eat food that may have been exposed to rodents and possibly contaminated with their urine. 

Dr M Areshkumar, MVSc, MSc, PGDORT

Research Associate, TANUVAS